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Stress and Cognition
Final Report
STRESS AND COGNITION: A COGNITIVE
PSYCHOLOGICAL PERSPECTIVE
National Aeronautics and Space Administration
Grant Number NAG2-1561
Lyle E. Bourne, Jr. and Rita A. Yaroush
February 1, 2003
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Outline
Stress and Cognition: A Cognitive Psychological Perspective
Introduction
Cognition in Emergency and other Abnormal Situations
Acute and Chronic Stress
Teamwork under Emergencies
The Purpose of this Review
Preliminary Guidelines from Cognitive Psychology
An Example
Research Methods
Measures of Stress Effects
Neuro-physiological Measures of Stress
Self- report Measures
Performance or Behavioral Measures
Conclusions
Definitions of Stress
Theories of Stress and Cognition
Conclusions
Arousal and Performance.
Motivation and Arousal
Stress and Arousal
Stress States: Qualitative Effects of Stress
Conclusions
Appraisal
Conclusions
Attention and Perception
Inhibition and Attention
Perception and Cue Utilization
Vigilance
Conclusions
Stress and Cognition
Memory
General Stress Effects on Memory.
Cortisol and other Neuro-biological Considerations..
Context And State Dependency involving Stress.
Other Considerations
A Memory Constriction Hypothesis
Conclusions
Environmental Conditions that Induce Stress
Time Pressure
Work Load and Overload
Fatigue and Sleep Deprivation
Noise
Ambient Temperature
Miscellaneous Stress Variables: Extreme Environments
Conclusions
Individual Differences Variables
Trait Anxiety and Stress
Other Personality Variables
Health and Coping Styles
Conclusions
Stress Countermeasures
Task Conditions
Stress Management
Conclusions
Other Reviews of the Literature
Summary and Conclusions
References
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Stress and Cognition: A Cognitive Psychological Perspective
Lyle E. Bourne, Jr. and Rita A. Yaroush
University of Colorado
Complex operations can be performed successfully in Space by human beings, but more slowly than doing the same tasks on Earth (Fowler, Comfort & Bock, 2000; Watt,
1997)), Fowler, et al. (2000) and Manzey (2000) propose two hypotheses to account for this performance degradation—(1) the direct effects of microgravity on the central nervous system and the motor system of the body and (2) the non-specific effects of multiple stressors. Evidence available to date is consistent with both hypotheses and further experiments are required to settle this question. The issue has practical implications because the countermeasures needed to ameliorate or prevent performance deficits will differ according to which hypothesis is correct. Understanding and ameliorating performance deficits will surely help ensure safer operations aboard the
International Space Station and during a mission to Mars.
Introduction
To the extent that the effects of multiple stressors are involved in the degradation of human performance in Space, as suggested by the results of Watt (1997) among others, cognitive psychology can help solve the problem. In a retrospective piece, Rapmund
(2002) describes how 20 years of experience working in the Pentagon convinced him of the need for a greater understanding of human behavior and of human-machine interactions to improve military operations. Wastell and Newman (1996) have argued that a well-designed military system should realize the twin aims of enhancing human performance and lowering stress. Success in this endeavor, they demonstrate, depends on the degree of support and controllability the system affords the operator.
Cognitive psychologists study things that people do in their heads and how they subsequently perform based on those mental operations. Cognitive psychology is largely an academic discipline and a basic science, concerned primarily with (a) identifying analytically the fundamental components of mental life, such as attention and its allocation, memory systems, problem solving, decision making and the like, (b) constructing experimental paradigms to isolate and examine these components in the laboratory, and (c) developing theoretical structures that help to make sense of the data collected in these paradigms. But the field is not exclusively academic. General principles have been uncovered over roughly the last forty years of laboratory research on
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cognition and some of those principles show promise of fruitful application to natural situations, especially in education and training.
Cognition in Emergency and other Abnormal Situations
One important issue to which contemporary cognitive research might usefully be addressed is behavior under stress and in emergencies or other abnormal situations.
Interest in this problem is not new, having been expressed throughout the history of psychology as an independent discipline and particularly by governmental agencies and the military, which are especially concerned about performance of people in extraordinary conditions (see, eg., Dearnaley & Warr, 1979).
Emergency situations are almost always dynamic, because early actions by a participant determine the environment in which his or her subsequent decisions must be made. Further, features of the task environment may change independently of the participant’s actions. Emergencies are time-dependent, because decisions must be made at the correct moment in relation to environmental demands. Emergencies tend to be complex, in the sense that most variables are not related to each other in one-to-one manner. Finally, emergencies are stressful, because they can create intense psychological pressures on participants.
Acute and chronic stress
Emergencies typically are not single isolated events. They are more like episodes extending in time. Thus, emergency situations often require not one decision about how to react, but a long series of decisions, and these decisions are, in turn, at least partly dependent on one another. For a task that is changing continuously, the same action can be definitive at one moment and useless at another. People often perform badly in emergencies, sometimes neglecting to respond correctly in even the most obvious ways.
One bad decision can worsen the situation and augment the importance of later decisions.
A poor decision or an inadequate response can compound the stress effects that are a consequence of the emergency itself. Being able to respond rapidly and correctly is clearly a distinct advantage to anyone caught in an emergency. Neufield (1999) has recently offered a promising formalism, based on nonlinear dynamics, that helps us understand the interaction of multiple variables operating over time, as in emergencies and in cases of stress and coping with stress. But there are presently few data available to test the adequacy of Neufield’s theory.
Emergencies often create acute conditions of stress, but these effects subside after the emergency has passed. Other conditions that are non-normal but might not involve
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emergencies can also be stressful. Many of these conditions generate longer term or chronic, in contrast to acute stress. Among these conditions are space flight, confinement, isolation, and other similar protracted exposures to abnormal circumstances.
Anecdotally, human beings have demonstrated an exceptional ability to live, work, and adapt to extreme environments. Sauer, Hockey, and collaborators conducted a series of studies of health and performance changes in chronically stressful circumstances. For example, Sauer, Juergen, Hockey, and Wastell (1999) reported a study of three Russian cosmonauts, tested on a PC-based simulation of a MIR space flight, including isolation and confinement over time. They found some temporary performance degradations as time passed although for the most part, without the occurrence of emergencies, job performance was acceptably high. The same researchers also reported on the effects of wintering-over by a group of French Antarctic expeditionaries. They, like Brubakk
(2000), argued that polar expeditions provide a better, more natural model of life in Space than do confinement or isolation studies. Again, only small decrements in performance on cognitive tasks were observed. Zulley (2000) reviewed the results of experiments performed in a wide variety of long-term isolating environments including Space, focusing on the circadian course of variables such as body core temperature, sleep-wake patterns, mood, and performance. He concluded that subjects in isolation can experience disturbances of sleep, mood and vigilance if their biological rhythms run "out of phase."
On the basis of his review, he recommended that, if at all possible, a strict 24-hr. time schedule should be kept with regard to environmental, as well as behavioral influences to insure adequate and restful sleep and optimal levels of waking performance and psychological well-being. Again, no serious degradation in performance tasks attributable to isolation was reported, however.
The job of a commercial airlines pilot is generally regarded as one of the most stressful. It would, therefore, not be surprising to discover that pilots suffer more health problems than non-pilots. Nicholas, et al. (2001) investigated self-reported disease outcomes among a large group of active and retired commercial airline pilots in the
United States and Canada. Increased disease rates among pilots were suggested for melanoma, motor neuron disease, and cataracts. However, rates for other diseases were in general lower than those for the U. S. population. As with others who are exposed to stress over extended periods of time, commercial airline pilots appear to adapt well and to evidence few serious behavioral problems as a consequence of job-related stress.
The counterintuitive message from this research seems to be that if participants are well prepared for the required tasks and understand that their confinement or isolation, while protracted, is time-limited, performance holds up well. Adaptation to chronic stress might be quite good, if the stressful situation is not prolonged indefinitely. If adverse conditions do persist, however, and there is no clear end-point to the stressful
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circumstances, there are at least some indications of possible significant cognitive effects, especially in children (Haines, Stansfeld, Job, Berglund, & Head, 2001), What unique effects emergencies, occurring during chronically stressful conditions, might have are not clear from these studies. However, it is also the case that prolonged work stress in relatively mundane work settings can have significant effects on a person’s health, especially if the stress creates chronic supra-optimal levels of arousal accompanied by a state of strain in the worker. Straining has been shown to put the performer at some risk regarding health and/or safety (e.g., Andries, Kompier, & Smulders, 1996). High correlations have been found between work stressors and psychosomatic complaints, general health, and felt fatigue and boredom at work (Houtman, Bongers, Smulders, &
Kompier, 1994).
Teamwork under Emergencies
Many emergency situations require teamwork and co-ordination among two or more players. Cockpit emergencies, for example, usually do not happen to a single individual but rather to a crew. The stress associated with the emergency is generated within each crew member, but its most important influence might be on the performance of the crew as a whole. Decisions and responses might be made by individuals but their effects ramify throughout the team. Thus it is imperative to try to understand not only the individual under stress but also how the team functions cognitively in these circumstances. Unfortunately, the literature on this issue is quite limited and largely inconclusive. The Purpose of this Review
Research in cognitive psychology has made a contribution to a understanding of acute and chronic stress effects on performance by identifying some of the factors that contribute to operator error under emergency or other abnormal circumstances and by suggesting how operators might be trained to respond more effectively in these circumstances. The major purpose of this paper is to review the literature of cognitive psychology as it relates to these questions and issues. Because older reviews are available (e.g., Hamilton, & Warburton (1979; Hockey, 1983), we limited our search of the literature to roughly the last 15 years (1988-2002). To anticipate our findings, research published in this time period, as well as the earlier literature, is limited in significant ways. There are many studies to document the effects of stress on cognition, performance, and health, and most indicate stress effects to be adverse. Typically, however, these studies compare only two conditions, stress and no stress. Outside of the clinical literature, there are very few studies that examine stress over a wide range of values. This itself is surprising in view of the fact that most theoretical accounts of stress
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effects in psychology invoke some variation of the inverted U-hypothesis, that is, that there is some optimal level of stress (or arousal) for performance in any task. To verify such a hypothesis, at least three levels of stress must be included in the experiment. The literature is limited in still other ways. Although there are many experiments to document that stress does influence performance, there are very few that assess ways to prepare for or to countervail the effects of stress. That is, we know very little about steps that might be taken to inoculate the performer against stress. There is some literature on training to manage stress when it occurs, but only a few of these studies touch on the benefits of stress management for cognition or performance. Thus, in anticipation of the review to come, its outcome, in the form of a clear and well-documented depiction of the stress/cognition relationship and of recommendations for procedures or guidelines that might be followed to minimize or eliminate adverse stress effects, will be disappointingly meager. As an aside, we expected to find the most significant research on stress and cognition published in the major cognitive journals, e.g., Cognitive Psychology, Memory
& Cognition, the Journal of Experimental Psychology: Learning, Memory, and
Cognition, and similar others. In fact, however, there has been relatively little published on stress in these Journals in the last 10-15 years. Rather, the most important publications that we found appear in peripheral journals, e.g., Aviation, Space, &
Environmental Medicine, Ergonomics, Work & Stress, and the like. There are also many unpublished technical reports available in various data bases. Our review uses few of these technical reports for a number of reasons, most important among them being their lack of peer review and the fact that the best of them often appear later in revised form in a peer-reviewed journal.
Preliminary Guidelines from Cognitive Psychology
An emergency, especially a life-threatening emergency, is a unique challenge to operators of complex systems, such as aircraft. On the one hand, pilots and crewmembers are expected to maintain a high degree of proficiency in the relevant emergency procedures, such that their performance is virtually automatic. Yet, on the other hand an air crew rarely has an opportunity to practice these procedures in natural circumstances.
In aviation, normal flight procedures that are carried out on a daily basis are completed with the benefit of a physical checklist. Emergency procedures, in contrast, are expected to be performed rapidly, accurately, and without external guidance. In addition, the procedures required might not be known if the conditions of emergency are unique.
Studies of memory, conducted within the context of the cognitive psychological laboratory, have a good deal to say about this difficult situation. For one thing, it is not feasible to expect that even a highly experienced operator can execute flawlessly a
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complicated sequence of actions, which have not been recently refreshed, in response to an unexpected and threatening event (Bahrick, Bahrick, Bahrick,& Bahrick, 1993; Healy
& Bourne, 1995). We will attempt to review and organize this experimental memory literature in such a way that the general principles can be identified and translated into guidelines for cockpit procedures. To the extent that we are successful, the result should have important implications for procedures and checklist design and for air-crew training.
Cognitive psychology has produced some promising leads on the effects of stress on human performance. Consider the most general question, what is the nature of responses under stress? The answer is, there is a vast amount of variability in performance. This variability depends, among other things, on who the operator is (a matter of individual differences) and on the situation in which responding takes place
(especially, the type of stress, e.g., time pressure, external threat, etc., engendered).
There is evidence for a continuum of performance, ranging from: (a) no effect (the person handles the emergency situation as he or she would in the absence of stress) to (b) facilitation (a small amount of stress actually improves performance), to (c) varying degrees of degradation (the person makes errors or inadequately slow responses) to (d) choking (characterized by performance failure due to “overthinking” the problem and attending to aspects of the situation that are irrelevant to the task at hand) to (e) outright panic (resulting in primitive ineffective responses, as if no training had ever been given, or complete paralysis). It is obvious that, quantitatively, the intensity of stress elicited by an environment event should move people, in general, from the no effect through various intermediate stages to the panic end of the continuum. It goes without saying that, to determine this effect, objective measures of stress intensity are required. Moreover, people differ in how they respond to the same environmental event. We expect that, by disposition, some people handle stress better than others, and we will present in later sections some organized documentation to that effect. In addition to dispositional sources, individual differences created by training also affect where a person falls on the performance continuum. Degree of original learning or overlearning on the task at hand probably can mitigate some effects of stress, especially at lower stress levels. It seems obvious that skilled procedures that can be engaged on demand and executed flawlessly under normal circumstances stand the best chance of succeeding in an emergency or other abnormal situations. The literature to back this conjecture up will be reviewed.
Assuming that stress generally will, at some point, degrade performance, even well-trained performance, where in the cognitive system are these effects most likely to be found? Perception, attention, memory, decision making, problem solving and response execution, all stages that have been identified and studied by cognitive psychologists, are candidates for degradation. There is a relevant basic science literature on these cognitive processes, both empirical and theoretical. But the relevance of this
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literature to the natural emergency situation is limited by two factors. First of all, cognitive psychologists, in addition to identifying the underlying processes of cognition, have developed laboratory tasks in which to study them individually, more or less uncontaminated by other processes. Thus, there are “attention” tasks or “memory” tasks in which attention or memory is revealed while other processes are eliminated or controlled. These tasks have become standard and are used widely over different laboratories. This has the advantage of providing a check on the replicability of data collected in different locations replicable. But, at the same time, it entails the disadvantage of creating relatively simple tasks that bear little face resemblance to things people do in the real world. Secondly, it is difficult to create real emergencies in the laboratory. Stress manipulations used by cognitive psychologists are mild and marginal, relative to natural emergencies. Both limitations make generalizations from the laboratory to behavior in natural emergencies risky and questionable.
To date, cognitive psychology has shed little light on performance in situations that require the concurrent management of multiple skills. Piloting an airship is one such situation that is characterized by many relevant variables, differing lags in system components, and several independent, simultaneous tasks. O’Hare (1997) and Wickens
(2002) have written extensively on this matter. At the top level, successful performance in piloting requires simultaneous awareness for one’s position in space, of the state of the many variables comprising the operations system, and of the various task requirements.
These competing demands often exceed the operator’s finite attentional resources. The
PC-based WOMBAT-super(TM ) Situational Awareness and Stress Tolerance Test has been designed to measure individual aptitude to cope with such demands (O’Hare, 1997).
Because of the high mental workload imposed by flight, a pilot might fail to maintain full awareness of the environment and, at various times, neglect certain critically important component tasks. Performance on the WOMBAT test reliably distinguishes between elite pilots and similarly experienced but less skilled pilots (O’Hare, 1997). Loss of awareness has been identified as a major contributor to human error in aviation accidents (Li, Baker,
Lamb, Grabowski, & Rebock, 2002). Moreover, there is no doubt that loss of awareness can be stressful. Indeed, anticipation of possible loss of awareness might be stressful, leading to some cases of performance degradation or errors as arousal increases.
Wickens (2002) has described the cognitive processes involved in piloting an aircraft and the changes in them that come with cockpit challenges. He notes that basic experimental cognitive psychology has produced a reasonable understanding of these processes in isolation or in simple (dual task) combinations. But presently we lack a full understanding or successful modeling of the complex interactions among these processes that occurs in many natural situations.
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That having been said, it is still the case that basic cognitive research has identified some important general principles regarding stress and performance. These principles are known to apply when individual cognitive processes are isolated and studied analytically.
To the extent that these processes are involved in more complicated naturalistic emergency situations, the principles so identified have something to say about behavior in emergencies. In other words, they should help us to understand and account for behavior of persons in real situations. Beyond that, we will be able to abstract out of this basic literature some useful recommendations about procedures and guidelines for effective performance in real emergency situations.
An Example
An example might be useful at this point. Cognitive research currently is concerned with a variety of forms of memory. One important distinction applies to the temporal focus of information retrieved from memory. This distinction is based on a continuum from the remote past – retrospective long term memory – to the present or near present – short term memory and immediate or working memory – to the future – prospective memory. Long term memory is theoretically a repository for facts and skills acquired in the past. Short term and immediate memory holds facts and skills that are currently at the focus of attention. Prospective memory contains reminders of actions to be executed at some future time and place. Laboratory tasks have been invented to study each of these forms of memory and the factors that influence them. The fundamental processes and the important variables influencing memory are not necessarily the same in all cases. Long term memories are characterized, for example, by loss of detail and partial retrieval whereas immediate memories and especially prospective memories are more likely to be all-or-none, i.e., complete or absent. Whether the memories in question relate to facts (episodic memories) or skills (procedural memories) is also an issue.
Specific fact memory tends to blur into generic representations over the long term, whereas skill simply degrades to lower levels of achievement.
Stress effects have been studied in the context of various forms of memory, although the data available are surprisingly skimpy. The evidence seems to suggest that stress in general (including stress arising in emergency situations) causes the operator to focus on the here-and-now, with consequent degradation in retrospective and prospective memory. The results are consistent with a memory constriction hypothesis to the effect that the time span from which knowledge can easily be retrieved and used in a given context shrinks as stress level increases. Neglect of facts or procedures in long term memory and failure to execute required behaviors at appointed future times might be major reasons for performance errors or failures in emergencies. At the present time,
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empirical evidence to support this hypothesis is weak. The hypothesis could, however, serve as a framework for future research efforts.
Research Methods
In the review that follows, our focus will be on the basic science literature. But we will not exclude naturalistic observations and case studies. To the extent possible we will examine the naturalistic decision making and problem solving literature in an attempt to find parallels with what has been learned in the laboratory. In fact, as noted above, the basic literature in cognitive psychology is quite disappointing. Basic researchers seem to have lost interest in stress during the last 15-20 years, judging by the number of publications in the prime journals. Consequently, we have broadened the search, and will reference articles in sports psychology, health, organizational and industrial psychology, human factors, aviation psychology, psychophysiology, ergonomics and other areas. We have found a considerable literature on situation-specific stress, as in stress in the workplace, in the office, among high level managers, in military operations, in airplanes, among air traffic controllers, in autos while driving, in buses, among police and firefighters (see, e.g., Raggatt & Morrissey, 1977; Westman, 1996; Westman & Eden,
1996; Zeier, 1994), but again the general implications are limited.. The research in these peripheral areas tends to be limited and a little simplistic, involving two-group comparisons (stress/no stress), biological correlates of stress, case or correlational studies, intervention studies, and while the literature is considerable, it does not tell us much about basic or practical principles.
Measures of Stress Effects
Neuro-physiological Measures of Stress
Situations capable of initiating physiological stress responses are varied and complex. In the animal literature, stressors have been classified into two categories
(Herman & Cullinan, 1997). One category, termed “systemic” stressors, includes many situations that produce direct physiological threats to organisms. Instances of such situations include microbial infections, temperature extremes, dehydration, injuries, and malnourishment. The second category, termed “neurogenic” or “processive” stressors, includes situations that do not immediately threaten an organism’s physiological homeostasis but are perceived as a potential threat. In human beings, instances of processive stressors include psychological and psychosocial situations, requiring significant cognitive processing for their interpretation. In the lives of human beings, the most common challenging situations encountered are in the processive category.
Traumatic-life events such as bereavement or anticipated or actual loss of home are
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familiar examples, but less traumatic events, such as performance anxiety associated with public speaking and examinations, as well as psychosocial pressures from interpersonal relationships and work place settings, are also effective activators of physiological stress responses. Most challenging laboratory situations fall into the processive class of stressors. Such laboratory settings range from cognitive situations demanding high levels of performance on mental arithmetic or the Stroop color-word interference test, to psychosocial situations involving public speaking, interviews, and the presentation of violent videotapes. Biondi and Picardi (1999) in a recent review of the human literature regarding the effects of real-life and laboratory stressors on neurohumoral functions, emphasized the importance of situational appraisal and emotional reactivity as triggers of several stress responses, as originally suggested by others (Lazarus, 1966; Mason, 1975).
The most emotionally “loaded” procedures are thus the ones associated with the strongest physiological stress responses. This association supports the need to examine self-report measures of stress and their correlation with physiological stress responses in future studies. There are several physiological responses that are reliably correlated with the experience of stress and with stressful physical stimuli. This repertoire of responses plays an important role in preparing individuals to cope with putative internal or external stimuli that might threaten their well being or survival. Threats to homeostasis are met by acute physiological responses that are quick and engage two main biological systems.
The first is the sympathetic division of the autonomic nervous system, which controls neural and hormonal processes. Acute psychological stressors generally activate the sympathetic adrenomedullary system. The release of the adrenomedullary catecholamine hormone, adrenaline, is crucial in the preparation of an individual’s “fight or flight” reaction, as first suggested by Walter B. Cannon in the early part of the 20th century.
Additional sympathetic neural activation via noradrenaline release is responsible for a variety of peripheral responses associated with stressful situations, including, but not limited to, increases in heart rate (HR), blood pressure (BP), respiratory rate, perspiration, and inhibition of digestive and sexual functions (Cacioppo, 1994).
The second principal stress-responsive system is the brain-pituitary-adrenocortical axis, which regulates the release of glucocorticoid (GC) hormones into general circulation (Akil, Campeau, Cullinan, Lechan, Toni, Watson, & Moore 1999). Two of the most salient hormonal responses to stress are increases in norepinephrine and cortisol,
GCs manufactured and released by the adrenal cortex. But stress is associated with a number of other neurohumoral responses. For instance, stress increases the release of growth hormone and prolactin and inhibits the release of the thyroid and sex steroid hormones. Many of these hormonal modulations have been linked to the release of cortisol (Nemeroff, 1992). The orchestration of these responses allows the inhibition of
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“vegetative” functions while activating energy metabolism, body defenses, blood flow to the skeletal muscles, and a sharpening of the senses. Farrace, Biselli, Urbani and Ferlini
(1996) have demonstrated the usefulness of these processes in the evaluation of stress responses during flight.
Stress also affects the human immune system. Although chronic stress typically produces suppression of a wide range of immune system parameters, acute stress has been found to stimulate certain aspects of immune functioning (McEwen, 2000).
Specifically, acute stress can trigger aspects of an immune system acute phase response, even in the absence of an infectious agent (Deak, Meriwether, Fleshner, Spencer,
Abouhamze, Moldawer, Grahn, Watkins, & Maier, 1997). This acute phase activation results in a rapid increase in blood levels of certain acute phase proteins, as well as production and secretion into the blood of the immune system related hormone, interleukin-6 (Zhou, Kusnecov, Shurin, DePaoli, & Rabin, 1993). Thus, acute phase activation is potentially another physiological marker of stress that might be useful in human studies. Recent animal studies have provided evidence for stress-induced stimulation of the acute phase response to be at least partially responsible for stressinduced impairments in memory consolidation (Cahill & McGaugh, 1996; Pugh, Nguyen,
Gonyea, Fleshner, Watkins, Maier, & Rudy, 1999). These studies support accumulating evidence for brain activity to be dynamically regulated by immune system factors (Maier,
Watkins, & Fleshner, 1994).
Electrical activity in the brain, as reflected in EEG patterns, are sensitive to certain abnormal human conditions such as alcohol intoxication and fatigue. Gevins and Smith
(1999) reported that both intoxication and fatigue reduced the accuracy of performance in a working memory task and that these effects were associated with changes in spectral characteristics of the EEG. These authors have shown that both human observers, operating intuitively, and computing networks trained on human data can discriminate
EEG patterns associated with fatigue and alcohol states from normal alert states with accuracy well over 90%.
Measures of physiological responses can serve at least three distinct purposes. First, they can help independently to determine the challenging or stressful character of experimental circumstances. They can be used to assess the degree to which the manipulations produce stress independent of the subjective exit interviews and self-report indices. These physiological measures may offer a rigorous between-experiment assessment of the stressful character of the different conditions employed in the laboratory. A second feature of these measures is that they permit an assessment of correlations between physiological and cognitive variables. For example, do the changes produced by stress in cognitive performance relate significantly to concomitant changes
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in particular physiological responses? Third, these measures will allow the investigation of possible mediating relationships between physiological states and cognitive functioning. For example, a given physiological state may not just mark stress but may mediate the effects of stress on performance. Intrinsic circadian variations of stressreactive hormonal levels could be tested to reveal possible mediating effects of such physiological states upon performance, although this research is yet to be conducted.
To measure physiological reactions to stress, the following procedures have been most frequently used and seem most useful. First, with respect to the action of the sympathetic nervous system, researchers have measured a variety of peripheral response measures, including, but not limited to, increases in HR, BP, respiratory rate, perspiration, and inhibition of digestive and sexual functions. These indices are probably most familiar as components of the lie detection procedure. Although they can be controlled cognitively, subjects typically have no reason to attend to these measures while engaged in a focal task. Under these circumstances, peripheral measures have proven to be highly and reliably correlated with other indices of stress level. There is a good deal of research to document the existence of distinct patterns of autonomic nervous system reactions to stressful events (e.g., Lovallo, Pincomb, Brackett, & Wilson, 1990;
Saab & Schneiderman, 1993). People who appraise potentially stressful events as challenges show a reaction consisting of high cardiovascular activity coupled with low vascular resistance. Individuals who appraise the same events as threats show low to moderate cardiac activity and high vascular resistance. Veltman and Gaillard (1996,
1998) investigated the sensitivity of some of the same physiological measures to mental workload in a flight simulator. Several respiratory parameters, HR variability, BP variability, and the gain between systolic BP and heart period all showed differences between rest and flight. Only heart period was sensitive to difficulty levels in the flight task. Among the respiratory parameters, the duration of a respiratory cycle was the most sensitive to changes in workload. Finally, the time between two successive eye-blinks increased and the blink duration decreased as more visual information had to be processed. Second, to tap the brain-pituitary-adrenocortical axis, researchers have measured GC cortisol in the saliva of human subjects. This is a noninvasive measure and can be repeatedly sampled in most experiments (Kirschbaum &
Hellhammer, 1994). Salivary cortisol is closely correlated with free plasma cortisol levels (Vining & McGinley, 1987), and is useful in detecting several forms of acute stress in the laboratory or in the field ( Aardal-Eriksson, Karlberg, &
Holm, 1998; Bassett, Marshall, & Spillane, 1987; McCleery, Bhagwager, Smith,
Goodwin, & Cowen, 2000), including challenging military training (Morgan et al.,
2000). Level of testosterone, which has been shown to be significantly reduced by
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some stress procedures (Elman & Breier, 1997; Hellhammer, Hubert, &
Schurmeyer, 1985; Schulz et al., 1996), can also be measured in saliva of male subjects. Similar determination using estradiol in adult women is usually not warranted because of low correlations between plasma and salivary levels with existing assays and collection methods ( Shirtcliff, Granger, Schwartz, Curran,
Booth, & Overman,2000)). The immune system cytokine product interleukin-6 (Il6), which is elevated in response to a variety of stressors, is another marker of stress measurable in saliva. Salivary Il-6 determination has been reported to correlate highly with the release of cortisol in at least one study ( Perez Navero,
Jaraba Caballero, Ibarra de la Rosa, Jaraba Caballero, Guillen del Castillo,
Montilla Lopez,Tunez Finana, & Romanos Lezcano,1999).
An important issue concerning the various hormonal responses to stress is the fact that cortisol shows a significant circadian rhythm in human beings (Czeisler &
Klerman, 1999). Thus, circulating cortisol levels normally rise and peak during early morning in anticipation of waking and the demands that the waking state produces on energy consumption and metabolism. Circulating cortisol levels thereafter drop throughout the day and are at their lowest in the evening, anticipating the reduced energy expenditure during the sleep period. Any activation of the adrenocortical stress axis is therefore superimposed on this daily rhythm, and the assessment of morning stress can easily be clouded by the already high morning circulating levels.
Despite the difficulties and the complexity of taking physiological measures, they are recommended for any research program that aims to provide a complete picture of the role of stress in human cognitive performance. It should be noted that the strength of a stressor can only be determined by measuring the subjective and physiological response of the individual, because individuals may vary widely in their reactivity to stressful circumstances. Where possible, it is important to determine the extent to which subjective reports of stress correlate with physiological measures. Likewise, it is important to see whether subjective or physiological measures of stress responses are reliable predictors of performance on whatever task is being studied.
Self-report Measures
Stress affects how we perform (behavioral), how we feel (self-report), and many of our bodily functions (neuro-physiological). All three then should be able to serve in some capacity as measures of stress, independent of environmental or physical conditions that are said to be stressful. Systematic and exacting
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experimental studies of stress and its effects on cognition require valid and reliable measures that can be taken both in the laboratory and in the real world. The best work available on the evaluation of subjective states of stress has been reported by
Matthews and his collaborators (e.g., Matthews, in press; Matthews, Joyner,
Gilliland, Campbell, Falconer, & Huggins, 1997).
Matthews et al. (1997) noted that research on the subjective state of stress, until recently, has been limited in scope, focusing primarily on state anxiety and mood. These authors developed a broader index known as the Dundee Stress State
Questionnaire (DSSQ) which provides the first comprehensive multi-dimensional assessment instrument for transitory states associated with stress, arousal, and fatigue. Construction of the DSSQ began with a factor analyses of various paper and pencil measures of stress, available in the literature or developed by the authors. These scales represented three primary categories which the authors refer to as mood measures (focusing on arousal, tension, and hedonic tone), motivation measures (especially intrinsic motivation or interest in the task at hand), and cognition measures (including awareness, interference, self-focus, concentration, and confidence). By factor analysis, these scales generated three secondary dimensions of subjective stress reaction. The first is labeled Task Engagement by the authors, and is described in terms of how much energy, and concentration a person invests in a task. The second is labeled Distress, that is, how much tension, the hedonic tone, and the confidence a person exhibits in task success. Finally,
Worry, or the degree of self-focus and self-esteem expressed and the amount of cognitive interference experienced from intrusive memories and other sources (see,
e.g., Baum, Cohen, & Hall, 1993). Refined scales were then developed to give maximally discriminant measures of Engagement, Distress, and Worry.
Matthews et al (1997) demonstrated empirically that these state dimensions are independent of other state or trait measures available in the personality literature, such as neuroticism. They further showed that these measures are sensitive to external stress manipulations, especially in challenging and demanding tasks. Task engagement scores are high when task demands are intense and the task itself provokes strong intrinsic motivation. Distress is most closely related to capacity overload and time pressure. Demanding tasks are typically distressing, especially when they are appraised as threatening. Finally, worry tends to be associated with self-evaluation as when the nature of the task provokes assessment of personal qualities and goals. But, boring or monotonous tasks or tasks that lead to a loss of concentration can also provoke worry. Matthews et al. (1997) have developed a processing efficiency theory that predicts slower memory scanning and retrieval in subjects with high chronic stress or high anxiety, because some of
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the working memory capacity of these subjects is occupied by worries, more than low anxious or nonstressed subjects. Ashcraft (2002) has attempted to test this theory directly, and reports inconsistent results. But the hypothesis is plausible and deserves further empirical investigation.
Basically, Matthews, et al. (1997) have shown that much of the variation in the subjective stress state can be characterized by the three themes, labeled commitment to the task, cognitive overload, and self-evaluation, all of which are accessible by self-report. Matthews (1996) suggested that these themes represent the t hree p rincipal a daptive c hallenges p osed b y s tressful p erformance environments and that basic state reactions reflect choices of adaptive strategy within a variety of different situations. The evidence supporting the validity and reliability of the DSSQ is extensive and impressive. As noted above, it represents the most comprehensive measure of subjective stress presently available. Its utility in research might be limited, however, by the length of the questionnaire and the time required to administer it, which is estimated to be approximately 10-15 mins.
If stress measures can be taken before or after the fact, then the questionnaire is probably t he b est i nstrument a vailable. I f s tress m easures a re r equired concurrently with stress conditions and/or on a moment-by-moment basis, other less reliable indices will probably be necessary. It might be possible to develop a short-form instrument, based in the DSSQ, that could be used for concurrent measurement, but such a test has yet to be published.
Task induced changes in stress are described within Matthews’ system as patterned shifts in task engagement, distress, and worry. Patterns are sensitive to task and environmental demands. Matthews et al. illustrated this effect with studies of automobile driving. Operators’ appraisal of task demands (workload) and choice of coping strategy mediate these stress effects. Thus, for Matthews, stress is an adaptive transaction between operator and task. Matthews et al. speculate that the consequences of task automation (e.g., cockpit automation) will vary widely depending on appraisal of the reliability and ease of control of the system, type and number of residual tasks left to the operator, and interpersonal factors such as personality and coping style. Thus there is likely to be no simple remedy for stress-related problems associated with automation, such as boredom or complacency. Fine-grained assessment of the operator’s feeling state and cognitions is required to determine vulnerability to performance degradation under stress. Stress and Cognition
19
Evidence from Matthews et al. (1997), based on self-report measures, supports the following guidelines for mitigating the effects of stress in automated and semi-automated systems, such as driving an automobile or flying an airplane.
1. Delineate and focus on those actions and problems that are subject to operator control.
2. Recognize that there are qualitatively different stress-reactions that require different interventions. Stress attributable to fatigue and task disengagement are different from those attributable to distress or worry.
3. Design the system with stress factors in mind. For example, avoid overload on operator controlled tasks.
4. Design for variablity of work load requirements.
A number of specific self-report techniques have been developed to measure stress in the work place, and some of these have possibilities as general stress measures. Quick (1998) has provided an excellent summary of these measuring devises, which include the following.
(1)
The Occupational Stress Indicator and its successor, the Pressure
Management Indicator (PMI, Williams & Cooper, 1998). The PMI presents a range of 22 sub-scales that tap into a number of aspects of the organizational stress process, from demands through moderators and modifiers to strain and distress responses. The PMI also provides information on organizational constructs such as organizational climate and individual constructs such as personal responsibility.
(2)
The Job Content Questionnaire (JCQ, Theorell & Karasek, 1996;
Karasek, Brisson, Kawakami, Houtman, Bongers, & Amick,.1998).), which is a perceptual measure of social and psychological characteristics of jobs and the content of work.
These questionnaires are reliable and valid self-report measures, but are less comprehensive, and therefore less valuable as research tools than the battery developed by Matthews et al. (1997).
How do self-report measures of stress stack up against neuro-physiological indices? Leaving aside for the moment the time it takes to recover these measures, the answer is, quite well. In fact, under many circumstances, self-report measures are to be preferred because of their greater face validity and reliability. There are several studies in the recent literature that speak to this issue. For example, Zeier
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(1994) reported a study that used both self-report and neuro-physiological measures of stress in air traffic controllers. He found that periods of high and low traffic differed in both self-reports and in levels of salivary cortisol. Further he found a high correlation between self-reports and cortisol levels. He concluded that, while these measures differ in substantive ways, the information they provide is supplementary and neither is to be preferred over the other. Both measures might be valid reflections of the same underlying processes.
Shostak and Peterson (1990) found that self-report measures of anxiety level were more sensitive and more reliable as predictors of simple laboratory performance than were two physiological measures, HR and BP. These researchers concluded that self-report measures were further to be preferred in this context because they were easier to take. Kozena, Frantik, and Horvath (1998) reported a similar outcome using middle-aged train drivers. Questionnaire data on health state and family health history, lifestyle, job stress, social and family support, personality characteristics, and health risk behaviors were more predictive of performance in reaction to laboratory stress than were measures of cardiovascular activity, including HR and BP.
Performance or Behavioral Measures
But the issue of which type of measure, self-report or neuro-physiological, is the better or more appropriate measure of stress effects is far from settled. Hancock and Vasmatzidis (1998) contend that, rather than either self-report or physiological measures, task performance level should be the primary criterion for determining the effects of exposure to stress. They argue that change in behavioral performance efficiency is the most sensitive reflection of human response to stress, and that error-free performance is the principal criterion of work efficiency, especially in high-technology systems. Therefore, continuing exposure to stress after work performance efficiency begins to fail, but before current physiological limits are reached, is inappropriate for both the safety and the productivity of the individual worker, their colleagues, and the systems within which they operate. Behavioral performance assessment should therefore supercede physiological assessment or self-report as the primary exposure criterion, although these other measures still provide important supplementary information.
There are, of course, others who disagree with this analysis, contending that how a person thinks and communicates about stress and/or how the body automatically reacts to stress are fundamental components of the stress syndrome that are not contained within measures of performance. Still, there have been
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several significant efforts, following the logic of Hancock and Vasmatzidis, which have been aimed at identifying and developing reliable performance measures to assess individual differences in reactivity to stress. Ackerman and Kanfer (1994) developed a battery of cognitive ability tests for predicting performance under stress. As a test bed, they used a dynamic Target/Threat Identification Task performed under time-pressure. Their final battery consisted of a mixture of cognitive and perceptual speed ability and stress-reactivity measures. They showed that these measures accounted for the major amount of individual differences in performance on a variety of complex tasks. Two tests, called The
Dial Reading and Directional Headings Tests, were found to be particularly promising predictors of performance in stressful information processing activities.
The authors concluded that such measures have definite advantages over selfreports in predicting individual differences in reaction to stress.
A somewhat different set of measures was used by Thomas, Schrot, et al.
(1995). Cognitive processes of primary interest to these authors were memory, speed of response, vigilance, mental calculation, reasoning, and learning. The measures of performance they examined were matching-to-sample, complex reaction time, visual vigilance, serial addition-subtraction, logical reasoning, and repeated acquisition of S-R associations. These measures were implemented in a standardized manner on portable battery-operated computers for use in both laboratory and field settings. Their report provides detailed documentation, supporting the reliability and the sensitivity of these measures to stress effects in a complex operations environment.
Conclusions1
Several physiological responses are reliably correlated with the experience of stress and with stressful physical stimuli. One arises in the autonomic sympathetic nervous system, which controls both neural and hormonal processes The second principal stress-response system is the brain-pituitary-adrenocortical axis, which regulates the release of GC hormones in the general circulation. Two of the most salient hormonal responses to stress are increases in norepinephrine and cortisol, GCs manufactured and released by the adrenal cortex. Third is the immune system, which is also sensitive to stress. Although chronic stress typically produces suppression of a wide range of immune system parameters, acute stress has been found to stimulate certain aspects of immune system function.
1
Conclusions are written in a smaller font than the text. They can be read after the section to which they relate or collectively, in a section entitled Summary and Conclusions, at the end of the report.
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Measures of physiological responses can serve at least three distinct purposes in research.
First, they can help independently to determine the challenging or stressful character of experimental circumstances. Second, they permit an assessment of correlations between physiological and cognitive variables. Third, these measures allow the investigation of possible mediating relationships between physiological states and cognitive functioning. To measure physiological reactions to stress, the following procedures seem most useful. First, with respect to the action of the sympathetic nervous system, researchers have examined a variety of peripheral response measures, including, but not limited to, increases in HR, BP, respiratory rate, perspiration, and inhibition of digestive and sexual functions. Second, with respect to the brainpituitary-adrenocortical axis, researchers have measured GC cortisol in the saliva of human subjects. The immune system cytokine product interleukin-6 (Il-6), which is elevated in response to a variety of stressors, is another marker of stress measureable in saliva.
The most successful self-report measures of stress focus on three processes: commitment to the task, feelings of cognitive overload, and self-assessment of success. Context-induced changes in stress result in patterned shifts in task engagement, distress, and worry on the part of the subject. Patterns are sensitive to task and environmental demands. Comparisons of the value of self-report to neuro-physiological measures of stress have been inconclusive. Most researchers find a high correlation between these two types of measures, leading to the conclusion that, while these measures differ in substantive ways, the information they provide is supplementary and neither is to be preferred over the other. Other researchers have argued that changes in behavioral performance efficiency are the most sensitive reflection of human response to stress, and that behavioral measures are sometimes preferable to both self-report and neuro-physiological measures.
Definitions of Stress
Stress is a descriptive term used in both the behavioral and biological sciences to cover conditions of a physical, biological, or psychological nature, that typically cannot be controlled by organisms, and that strain organisms often beyond their powers to adapt (e.g., Gaillard & Wientject, 1994). But there is no single universally agreed to definition of stress and consequently no single measure that will tell us when a person is stressed or operating under stressful conditions
(Hancock & Desmond, 2001). Some conditions have generally been accepted at stressful. For human beings, these include but are not limited to extreme temperatures, loud or noxious noises, infectious diseases, sleep deprivation, extreme heavy or prolonged work loads, time pressures, social pressures, and intense negatively-toned emotions. Stressors are environmental, biological, and/or cognitive events that, among other things, challenge or threaten the well-being of an organism, increase its arousal or activation level, and deplete its resources (see,
e.g., Hobfoll, 1991). They can be extraneous (non-work stress) or indigenous
(stress created by the task) and they can arise from endogenous or exogenous sources. The resulting stress states can be acute and time limited, as in responses
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to a single transitory event, or they can be chronic, as when the condition of stress persists in time. Normally, human beings respond to stressors either through extraordinary mental or physical effort or by exhibiting degraded performance.
Extreme effort over time in response to chronic stress can result in either mental or physical exhaustion or injury (see, e.g., Kolich & Wong-Reiger, 1999).
With respect to human performance, stress-related phenomena are often classified as emotional, cognitive, and physical (Van Gemmert & Van Galen,
1997). There are numerous examples of the effects of stressors in all three categories affecting human performance. For example, regarding emotional stress,
Adam and Van Wieringen (1988) have shown that worry and emotionality, measured as personality traits, are negatively correlated with proficiency in a simple motor task. Cognitive stress, resulting from the need for coordinated multitasking in nearly all daily activity, is perhaps the most common stress condition.
Heightened mental load resulting from multitasking typically slows responding, although it often has little affect of accuracy of performance (Castiello & Umilta,
1988). Physical stress is particularly interesting in the light of the contemporary concern with the quality of the natural environment. Urban areas in particular present stressors in the form of noise, air pollution, and disturbance of natural light/dark rhythms. But research has presented an unclear picture of the effects of these stressors, sometimes reporting significant detrimental effects on performance and health and sometimes reporting no effect (Nivison & Endresen, 1993; Smith,
1991). Interestingly, Van Gemmert and Van Galen (1994) showed that performance in a complex sensory-motor task was more sensitive to cognitive stress, manipulated by concurrent memory load, than to physical stress, manipulated by sound pressure level. These often conflicting results argue for a more comprehensive study of stress effects on human performance and for an integrative theoretical framework in which to organize the empirical evidence.
This effort might profitably focus on the nature of the task to be performed and the strategies people use to contend with conditions of stress.
Theories of Stress and Cognition
In general, theories of stress account for its effects on cognition and on human performance in terms of multiple psychological and biological processes.
These processes include, but are not limited to: arousal or activation (stress intensity is directly and linearly related to arousal level), attention allocation
(stress controls directly or indirectly the distribution of attention across points of environmental and internal input and can overload attentional capacity), and plans or strategies for the deployment of attention and other resources. Theories differ
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in their assumptions about these processes. Some attribute little or no role to consciousness or awareness, asserting that stress effects are direct, automatic, biological, or intuitive. Others assign the major performance control functions to plans, appraisals, analyses, and other cognitive phenomena that are invoked in stressful situations. These differences are illustrated in the following section, which presents a sampling of recent theoretical writing on the relationship between stress and cognition.
Cognitive Continuum Theory. Hammond (2000) introduced what he calls a missing link in modern stress/cognition research, that is, a comprehensive set of principles under which stress effects can be classified, interpreted, and coherently integrated. Such a set of principles, if it can be articulated and agreed to, would be tantamount to a new theory and constitute a model for future research in the area.
To set the stage for his theory, Hammond argues that the field has been characterized by two points of view regarding the proper focus of research (for a related argument, see Gigerenzer, Todd, and the ABC Research Group, 1999).
The Coherence point of view incorporates models based on the assumption that human behavior is always contingent not only on the task at hand but also on intervening rational or quasi-rational thought processes. Models of this type include those based on statistical decision analysis, heuristics and biases, information integration theory, and the notion of multi-attribute choice. The coherence position leads to a research focus on the systematic interplay between a task or problem, thought processes it might elicit, and the eventual response. The
Correspondence viewpoint incorporates models that are indifferent to intervening cognitive processes and that focus on systematic and direct relationships between task characteristics and responses, e.g., the empirical accuracy of a judgment. The theories cited as examples by Hammond are signal detection theory, probabilistic mental models, and the author’s work on social judgment theory. The first approach emphasizes analytical cognition (deliberate cognitive processes) and the second approach emphasizes intuitive cognition (unconscious,, non-traceable cognitive processes) (see also Gigerenzer, Todd, & the ABC Research
Group,1999).
Hammond’s theory of judgment and decision making -- the Cognitive
Continuum Theory (CCT) -- is based on four principles, arising from the correspondence and coherence metatheories and two theoretical terms, called intuition and analysis. Of further importance to this theory is the postulate that
“tasks” are special concepts in and of themselves and have properties—“task properties” – that significantly interact with cognition. CCT requires the development of indices to codify both task properties and cognitive properties.
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This is accomplished by considering cognitive activity to lie on a continuum from intuitive to analytical with a mid-point of “quasi-rational thinking” or “common sense”. Tasks are likewise considered in light of their “capacity to induce intuition, quasi-rationality, or analytical cognition”. This then produces a 3X3 matrix of task and cognitive properties onto which a particular cognitive event can be mapped
COGNITIVE
INDEX
INTUITIVE
QUASIRATIONAL
ANALYTIC
TASK CONTINUUM INDEX
INTUITIVE
QUASIRATIONAL
Best
Best
ANALYTIC
Best (normal)
Stress is introduced into this model as a consequence of a disruption of
“constancy” or balance or homeostasis between cognition and task (environment).
Hammond proposes that all organisms seek to maintain stable relations within their environment and the disruption of stabilized relations produces what we know as stress. Stressors are divided into endogenous (any negative change within the task system, e.g. loss of an information source) and exogenous disruptions (those due to factors outside the task system (e.g., fire, noise, cold).
The particular disruption (exo- or endo-) will, according to Hammond, affect the type of cognition and the consequences of judgment. Overcoming endogenous disruption of constancy demands cognitive change, i.e., moving along the 3x3 matrix, whereas overcoming exogenous disruption of constancy demands resistance to cognitive change and staying within the correct cell of the matrix.
How to know when to “change” or when to “stay” within a particular cognitive mode becomes the crux of effective problem solving, leadership, and judgment.
The author contends that not only is this model highly researchable, but should also lead to methods of training that may be different for those being groomed for leadership roles.
Hammond claims that CCT provides a new orientation for the field of stress and cognition. He highlights four points: (1) Environmental events and cognitive events share equal and joint billing in the determination of behavior. (2) Stressors should always be examined in relation to cognitive activities. (3) Disruptions of homeostasis should be differentiated into endo- versus exogenous and the current cognitive mode recognized (intuitive/analytical). (4) Leaders and followers should
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be taught to be alert to and to accept the need for cognitive change. According to
Hammond (2000), these principles provide a cohesive and coherent framework for organizing what we presently know about stress and cognition and the direction that future research in might take.
Theories of activation and resource allocation. Many theories of stress incorportate two mechanisms, one related to activation of the organism and the other related to resource competition. The first mechanism is typically assigned a facilitating effect generally describable as a “readiness to respond.” The second can have a negative effect resulting from the necessity to spread cognitive or other resources thinly over various input and response possibilities. The combination of these two mechanisms allows the theorist to account for the sometimes paradoxical facilitative and inhibitive effects of the same stressor on performance. Facilitation occurs when the activation process dominates; inhibition when the competition process dominates. Facilitation generally occurs under mild to moderate stress and with simpler task requirements. Inhibition occurs at higher levels of stress and more demanding task requirements.
The form attributed to these mechanisms differs widely among theorists. A recent example is Van Gammert and Van Galen (1997), which is described here not because it is the most convincing theoretical argument but rather primarily for purposes of illustration of recent theoretical developments regarding processes underlying stress. Van Gammert and Van Galen employ the concept of neuromotor noise to explicate the activation side of stress effects. But they also incorporate resource allocation and postulate ways in which activation and resource allocation interact.
Van Gammert and Van Galen assert that the human cognitive system is inherently noisy. But increased processing demands produce even larger levels of noise and consequently decreased signal to noise ratios in the system. That stress generates noise in the cognitive system is not a new idea, being first introduced by
Mandler (1979). But Van Gammert and Van Galen develop the idea beyond earlier theoretical statements. According to Van Gemmert and Van Galen, the effects of noise can appear either in effectively reduced sensitivity to task related sources of information or on the motor side in the form of less exacting movements. Van Galen, Van Doorn, and Schomaker (1990), for example, showed that, as the complexity of the sequence of movements required by a task increased, the contribution of tremors and other indices of neuromotor agitation also increased, resulting in a relative degradation of performance. But not all effects of noise are negative. Noise is also said to have an activating or altering
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function. Performance is assumed to be best at optimal levels of signal to noise ratio. Performers engage in various strategies to achieve these optimal ratios.
One strategy is to slow down, permitting noise activation to level off relative to task-relevant activation. Evidence in support of this strategic maneuver comes from classical stress management techniques and from the considerable literature showing among other things that RTs to weak signals are typically slower than
RTs to stronger but otherwise equivalent signals (e.g., Tanner & Swets, 1954). A second stress management principle states that, under conditions of stress, performers adaptively set motor system parameters to produce optimal signal-tonoise ratios for muscles and movement.
Noise effects, when they occur in resource pools, can adversely affect all concurrent tasks drawing on those pools. Noise propagates in the cognitive system such that concurrent tasks are more affected by noise than are independent or sequential tasks. Further, the more closely related two or more concurrent tasks are, the greater the competition between them for resources. A potentially useful extension of this work has been provided by Neufield (1999), who developed a nonlinear formalism for describing multiple variables interacting over time, as in stress and performance.
Van Gammert and Van Galen (1997) tested some of these theoretical ideas in a series of experiments using both verbal (writing numbers in response to dictation) and spatial (aiming and drawing) tasks. Both tasks were performed under two types of stress, cognitive (performing a secondary arithmetic task) and physical (presence of a loud auditory noise). Three measures of performance were taken. Response initiation time, that is, time between stimulus and the beginning of movement, was used as an index of the difficulty of information processing. Movement time, that is, time to execute a response, was used as an index response difficulty. Hand pressure on manipulanda was used to measure tremor and motor stiffness. Both facilitative and inhibitory effects of stress were observed on initiation and movement time. Predictions from theory about resource competition, tremor interference, and time management were largely confirmed by these experiments.
Matthews and Desmond (1995) argue for a model of stress that incorporates three general mechanisms through which stress and the operation of complex systems may interact to affect performance, generally detrimentally. These are (1) overload of attentional capacity, (2) disruption of executive control of selective attention, and (3) disruption of adaptive mobilization of effort. These mechanisms were validated by Matthews and Desmond with data from driving simulator
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studies of stress and dual-task performance. Stress was investigated both through the experimental manipulation of certain environmental variables and the through measurement of individual differences in stress vulnerability. Variables that accentuate detrimental effects of stress include older age, inexperience at the task, and poor attentional skills. The results clearly support the role of attentional resource allocation as the major process mediating stress effects on performance.
The major limiting variable that is most clearly subject to the influence of training is inexperience. Indeed, providing experience with the task and the stressors that occur in it override the influence of age and attentional skills. These data have been taken to support the use of over-training as a countermeasure to stress.
A constraint. Hancock and Warm (1989) point out an important constraint that a general theory of stress and cognition will have to accommodate, namely, that various sources of stress from the environment don’t all impact performance in the same way. Conversely, the same stressor might be reacted to in different ways by different performers. Hancock and Warm examine, in particular, the differing effects on sustained attention of acoustic stress or noise in contrast to the performance patterns that emerge from the influence of heat stress. They note that the task itself, in this case vigilance, can be its own source of stress, and that an integrated view of stress and performance must consider the task as a primary influence in the generation of stress. This assertion is consistent with the role assigned to tasks in Hammond’s theory (2000). Any theory of stress must accommodate these multiple source of stress and their potentially non-additive effects of performance.
Conclusions
There is no shortage of theories about stress and it is impossible to review them all here.
Fortunately, there are a few common themes among these theories and this fact provides a way to categorize theoretical ideas. Some theories emphasize the biological consequences of stress, treating behavior as a by-product of biological processes. Examples include automatic neurological and/or hormonal changes that are triggered by an event. Others focus on the behavioral consequences of stress and on cognitions that mediate the stress/behavior relationship, including importantly how the “stressful” event is appraised by the organism. In general, theories account for stress effects on cognition and on human performance in terms of multiples of processes. These processes include, but are not limited to: arousal or activation (stress intensity is directly and linearly related to arousal level), resource allocation (stress controls the distribution of mainly attentional resources across points of environmental and internal input and can overload attentional capacity), and plans or strategies. Theories differ in their assumptions about these processes. Some attribute little or no role to consciousness or awareness, asserting that stress effects are direct, automatic, and intuitive. Others assign major performance control functions to plans, appraisals, analyses, and other cognitive phenomena. No theory that we have
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reviewed completely elucidates the stress process, and it is only reasonable to expect further attempts at theoretical explication is the future.
Arousal and Performance.
Arousal, alertness, and activation are terms used in the psychological literature more or less synonymously to describe a particular state of the organism.
Like any state, arousal is capable of variation in time. As an organism becomes more aroused, it likewise becomes more alert and more highly active, at least up to a point. Using a circadian analogy, sleep or initial wakening lies at the low end of the arousal continuum. The stimulation or sensory experiences attendant on waking enhances arousal level, and arousal level grows as daily events transpire.
Generally people experience the highest normal levels of arousal around mid-day, although meals can cause transitory decreases and unanticipated events can cause transitory increases or decreases in arousal during the day. Arousal levels decrease with prolonged work and attendant fatigue. The onset of darkness is associated with a return to resting levels of arousal as an individual prepares for sleep (see,
e.g., Neri et al., 2002).
Human performance in nearly all situations tends to be correlated with arousal, improving up to a point as arousal level increases and falling off as arousal decreases diurnally. But there are, of course, many qualifications on this general rule. For example, arousal level can become too high for the task at hand. When a person is over-aroused, performance will deteriorate. Moreover, simple tasks like vigilance, time estimation, or the execution of a single well-practiced manual response are performed optimally under relatively high arousal levels, whereas complicated tasks such as those involving a sophisticated level of mental calculation are performed optimally under relatively low levels of arousal. Thus, it has been known for some time that modestly increasing a person’s level of arousal,
e.g., by introducing the threat of a painful stimulus, facilitates performance on a simple task like time estimation (e.g., Falk & Bindra, 1954), but can hinder performance on more complicated tasks like public speaking or mental arithmetic
(see Giesbrecht, Arnett, Vela, & Bristow, 1993; Lovallo, 1997).
The correlation between arousal and performance is so ubiquitous that it has come to be accepted as a law in psychology – the Yerkes-Dodson (Y-D) law, named for its putative discoverers (Yerkes & Dodson, 1908). The law takes the form of an inverted U-shaped relationship between performance and arousal.
Performance on any task is best at some mid-level of arousal, falling off as arousal becomes too low or too high. The specific level of arousal that is optimal for
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performance differs among tasks, tending to decrease as task difficulty increases.
The lawful status of this relationship was solidified by Donald Hebb in his oft-cited presidential address to the American Psychological Association (Hebb, 1955).
Despite the intuitive reasonableness of this relationship and the vast amount of empirical support for it, there has been some skepticism. Hancock (1987), for example, pointed out that the Y-D law borders on the tautological, given that the result it expresses could hardly be otherwise. That is, performance in any task is bound to be poorer when the performer is under- or over-aroused. Some mid-level optimum follows necessarily. This controversy is irrelevant to present purposes, however, because we interested only in the descriptive feature of the Y-D “law.”
Motivation and Arousal
Arousal might affect performance simply by activating response systems.
An aroused organism is an organism that is ready to respond. Whether the activated response systems are relevant or correct for the task or irrelevant or incorrect determines whether arousal facilitates or impedes task performance. An alternative theory (see Lovallo, 1997) links arousal to motivation. The more aroused the organism is, the more it is motivated to perform well. Such a theory accounts easily for the initial upward leg of the Y-D law but requires interference or inhibitory processes to account for the possibility that an organism can be “too motivated” to perform well. Among the models that have been suggested are those that invoke activation of competing responses at higher levels of motivation
(Lovallo, 1997). Even though there might be a strong link between arousal and motivation, there is plenty of evidence that these are separable concepts. For example, Dyregrov, Solomon, and Fredrik (2000) have shown that performers can counteract the potentially degrading effects of supra-optimal levels of arousal by extra effort. Making an extra effort is surely a matter of motivation, which means that, in this example, motivation competes with arousal for control of behavior.
Countervailing influences imply unique and separable motivational and arousal processes. Stress and Arousal
Stress effects on performance are, in part and to some extent, mediated by arousal. Like arousal itself, stress can have either beneficial or degrading effects on performance, depending on the intensity of the stressor, the momentary level of arousal when the stressor occurs, the nature of the task to be performed under stress, the skill of the performer, and other variables. Light stress introduced while the participant is at some sub-optimal level of arousal has been shown to facilitate
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performance (e.g., Bourne, 1954; Falk & Bindra, 1954: Meyer, 1953; Spielberger,
1966, 1972). But one unique and important feature of stress is that it can induce high levels of arousal that are rarely seen in normal circumstances. Thus, often, stressors induce levels of arousal beyond optimal for performance in any task, and as a consequence, performance is degraded. Modest levels of supra-optimal stress can be counteracted by the performer by increased effort, resource mobilization, or straining (e.g., Dyregrov, Solomon, & Fredrik, 2000; Gaillard, 1993; Gaillard &
Wientjes, 1994; Hocket, 1997; Matthew, Sparkes, & Bygrave, 1996). Razmjou
(1996; see also Razmjou & Kjellberg, 1992) claims that resource mobilization involves deliberate processes, basically strategies for controlling effort, that allow the performer to adapt to the source of stress or arousal and to task demands.
According to Hockey (1997), successful performance in any task requires the operation of a control mechanism, which allocates resources dynamically.
Performance may be protected under stress by the recruitment of previously untapped resources, but only at the expense of increased subjective effort, and other behavioral and physiological costs. Of course, performance stability can be achieved by reducing goals, without further costs.
At some high level, however, stress will degrade performance. Under the pressure of an emergency, close examination by others, time urgency, threat of bodily harm, or other strong stressors, people often falter. Performance degrades, or worse fails. At the extremes of stress, a performer might “choke” or “panic.”
Stress States: Qualitative Effects of Stress
Quantitatively, stress effects on performance follow the inverted U-shaped relationship (the Y-D law). Although there is considerable evidence in support of such a relationship, the Y-D law is not the whole story and has limited explanatory value for a variety of reasons (e.g., Hancock, 1987). For one thing, not all empirical evidence is consistent with a U-shaped function of performance across levels of arousal (Westman & Eden, 1996). Secondly, as Hockey (1983) and
Hancock and Warm (1989) argued, every stressor produces its own unique pattern of effects on cognition and performance, making it unlikely to find an adequate allencompassing principle or theory. Further different stressors can interact, often producing nonadditive effects on performance (e.g., Hygge & Knez, 2001). Evans,
Allen, Tafalla, and O’Meara (1996) examined the interactive effects of multiple, sequential stressors on cognitive performance and psycho-physiological indices.
Subjects engaged in a relaxing or a highly stressful activity followed immediately by performance of a task under quiet or noisy conditions. Results indicated that the negative effects of noise on both concurrent and aftereffect performance and on BP
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were exacerbated by prior exposure to either a lab stressor (making a speech) or to a naturalistic stressor (college final examination). Thirdly, the Y-D law relates only to arousal or system activation and not to other processes such as interference and resource demands that might also be influenced by stress. Finally, and perhaps most importantly, Y-D law relates exclusively to simple quantitative measures of goodness of performance, e.g., speed or accuracy of response.
It is clear that stress creates qualitative changes in the organism and its performance, above and beyond those captured by the Y-D law. For example, at some point, stress increments begin to degrade performance. Initial degradation is graceful, that is, small and gradual reductions in performance as stress increases.
In extreme circumstances, the degradation in performance can be catastrophic, with a stress increment causing a complete system failure (Norman & Bobrow,
1975, 1976). Different stressors and different levels of stress act upon cognitive functions through different intervening states. There is need in a complete account to develop a descriptive or explanatory system that reflects these qualitatively different states.
We suggest that the concept of Stress State will help to elucidate the various
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ways in which stressful circumstances and feelings of stress influence human performance. The Stress State figure shown above serves as a useful guide to these effects. As previously noted, stress at low levels creates a state of facilitation.
Chappelow (1989) was able to show in an analysis of aircrew errors that cognitive failures are often associated as much with under-arousal as they are with overarousal. He found that performance actually improved with a little stress in the environment. At some point, stress for a given task and individual reaches an optimal state or level. Performance can be maintained at supra-optimal levels of stress if the performer can summon a higher motivational state, sometimes called a state of strain or mobilization (see, e.g., Doerner & Pfeifer, 1993). But, as stress increases even further, performance will eventually enter a state of degradation, and the performer will find him or herself less capable of adequate responding.
Performance degrades, but in a relatively graceful manner (Norman & Bobrow,
1975). Extreme levels of stress produce more than simple or graceful degradation in performance. Eventually, the effects of stress can become catastrophic. A experimental example of catastrophic performance degradation with stress, resulting in a choking or panic state, can be found in Lehner et al. (1997), These researchers reported that, with extreme time pressure, subjects stopped using decision making procedures they were instructed to use and reverted to more familiar, more intuitive procedures, even though these procedures resulted in inferior performance. These qualitatively unique stress states are not captured by the Y-D law.
It is important to distinguish between choking and panicking, two extreme kinds of performance degradation resulting from stress. Before elaborating on this distinction, consider the following. When you first learn how to do a particular task, like drive an automobile or play tennis, you think through each step in a deliberate and conscious manner. You learn the task explicitly and your representation of the task lies in an array of explicit memories. But, as you train more and improve on task, responses become more automatic and come to require less and less thought or attention. Performance becomes more fluid and skillful and is often conscious only in retrospect. The learning at this point achieves an implicit status and the representation of learned skill resides in implicit memory.
What you know about any task you have learned and practiced typically has representation in both an implicit and an explicit memory system.
Choking is a form of performance degradation that involves an unintentional transition from well-learned, highly practiced, essentially automatic action to a more time consuming, controlled form of responding. This is a transition that changes the basis of responding from an implicit to the explicit memory system.
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The consequence of this transition is often inferior, or at least slower performance.
Stress sometimes induces this transition, and that is what is meant by “choking under pressure.” When you revert to thinking about each step required by a familiar task, you lose your fluidity. You begin to perform slowly and cautiously, much as you did when just starting out to learn the task. You become a beginner once again and often perform like one, relying on memories that often have not been used in quite awhile. You are “overthinking” the situation. In sports, this is what coaches mean when they use the stock phrase “paralysis by analysis.” A player or the team fails because of over-analyzing the situation, rather than simply reacting. In one of a very few laboratory studies of choking, Beilock and Carr (2001) investigated the performance of golfers. One group of participants was trained to putt a golf ball with a video camera set up in front of them, under the instruction that professional golfers would review and critique the tapes. This condition was designed to adapt golfers to being in the spotlight, raising their self-consciousness and increasing their attention to their own performance under scrutiny. A second group was trained while listening simultaneously to a list of recorded words, under the instruction to repeat the word “cognition” whenever they heard it. This condition was intended to adapt golfers to being distracted while trying to putt. A third group was trained under quiet, nondistracting conditions.
After extensive practice designed to develop a high level of putting skill, participants took a test under both low- and high-pressure conditions. The idea was to determine whether training under distracting or self-focus conditions would improve golfers’ ability to perform better under pressure than normal training conditions. In other words, if you focus less than you normally would on the task at hand, which might happen when distractions are present, or if you focus more on the task, which might happen with greater self-awareness, does your performance under pressure suffer? In the low pressure test (no secondary task, no video camera, no audience), all three training groups performed equally well. In the high pressure test, in which a significant amount of money was contingent of excellent performance, the normal and the distraction training groups were significantly inferior to the self-monitoring group and performed worse than they had during training. The self-monitoring group actually performed better on the test than they had during training.
People under pressure are more stressed, anxious, and aroused and more self-conscious about their performance. Consequently, they try to exert greater conscious control over their actions, rather than allowing the skill they had
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acquired to guide their performance implicitly. There are numerous examples of choking due to heightened self-consciousness or other stressors in the sports literature and folklore, e.g., Greg Norman’s collapse in the final round of the
Masters’ Golf Tournament in 1996 or Jana Novatna’s last set loss to Steffi Graf at
Wimbeldon in 1993. Beilock and Carr (2001; see also Beilock, Carr, MacMahon,
& Starkes, 2002) argue that training in an environment in which one is forced to attend to performance from the outset can immunize the performer against the negative effects of pressure. Golfers in the self-monitoring group were protected from choking because, during training, they had adapted to the impact of conscious self-awareness and were able, unlike participants in the other two groups, to rely on implicit procedural memories to guide their performance. They were better able to “go with the flow,” undeterred by extraneous stressors. Without such training, choking is a possible consequence of intense social, competitive, or other pressures. Panic is a different stress state, and typically results in a more severe form of performance degradation than choking. When panic occurs, behavior becomes primitive; if the person thinks at all, it is maladaptive automatic thinking (Katz &
Epstein, 1991). Panic is not just a matter of reverting to behaviors that had been learned earlier or to memory representations in an explicit form. Panic is characterized by an even more rudimentary, instinctive kind of behavior aimed at survival. Rather than “overthinking” the situation, a panicked person stops thinking altogether and is inclined to react in the most basic way to get out of the situation or to escape the stressor. Stress appears to cause explicit memories to become unavailable or irretrievable. In a panic state, short-term memory seems to cease functioning. The person just freezes, that is, fails to respond, responds in an automatic but unskilled way, or reverts to primal instincts . Moreover, high arousal, as under stress, results in perceptual narrowing (Easterbrook, 1959). The range of cues or sources of informational input that an organism might use to escape the situation is reduced. The panicked individual focuses, indeed often obsesses on one aspect of the environment, usually to the neglect of information that could eliminate the stressful condition. The consequence is that, even though the goal is survival, performance is functionally maladaptive (Katz, & Epstein,
1991). To use another bit of sports jargon, coaches have been known to refer to a state of panic as “brain lock.” The cognitive performance system is locked down.
Conditions of panic are virtually impossible to create in the cognitive psychology laboratory. Thus, most of what we know about panic under stress comes for case histories and self-reports. Good examples come from SCUBA diving and sky diving. Skydivers have two parachutes and are trained such that, if
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the primary chute fails to open, they should immediately pull the cord on the secondary chute. There have been reported accidents resulting from a failure to do so. People have been found dead or injured on the ground still clutching the cord to the primary chute. Apparently, these victims pulled the cord for the primary chute and, when it failed to open, panicked, continued to tug, but never thought about the secondary parachute. Other poignant examples from piloting can be found in Langewiesche (1998).
Panic is clearly a state to avoid, if one is to escape an emergency situation.
The question is, can we develop training routines that minimize the likelihood of panic in situations that are susceptible to emergencies. On the basic research side, we need to develop experimental paradigms, building on the work of Beilock and
Carr, that permit the establishment of choking and panic states under laboratory conditions. There seems to be little evidence of that possibility at this writing.
Conclusions
There is a close relationship between stress and arousal. Stressful events are arousing, causing attendant changes in states of the organism, in cognitive processes, and in performance.
Of greatest relevance to behavior in emergencies are the stress states of (1) strain or mobilization, wherein the person recruits untapped resources to maintain performance levels when arousal is supra-optimal, (2) degradation, wherein mobilization fails and performance suffers but only gradually, (3) choking, wherein performance might fail as the organism overthinks the tasks at hand, and (4) panic, wherein performance reverts to non-cognitive primitive modes of behavior. Research has established the basic parameters of these states, but little is known in detail about situations and individual differences that are conducive to them or about the cognitive difference among them. This fertile ground for future empirical research.
Appraisal
Lazarus (1990; see also Lazarus & Folkman, 1984) developed a comprehensive cognitive model of behavior in response to stress. That model is based on the fundamental assumption that a potentially stressful life episode does not actually create stress unless it is appraised as threatening. That is, the ways people think about situations determine how they respond emotionally and how they cope with those situations.
As reasonable as it might sound, many of Lazarus’s postulates have received little empirical attention, and some of the existing research has yielded contradictory findings. For example, Zakowski, Hall, Cousino-Klein, and Baum
(2001) conducted a longitudinal study to clarify the associations among feelings of
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control, appraisal, coping, and stress. Lazarus’s theory postulates that coping strategies tend to match the level of appraised controllability of the stressor
(matching hypothesis). Recall that Hammond’s (2000) theory contains a related postulate to the effect that a match between strategy and task renders a situation non-stressful. An alternative to Lazarus’s expectation is the main-effects hypothesis, which states that problem-focused coping is generally more effective in reducing distress regardless of appraisal. These hypotheses were tested by
Zakowski et al. with 72 adults who completed questionnaires on coping, control, and appraisal. Stress was assessed using both a self-report and a behavioral measure at two different times approximately 2 months apart. The matching hypothesis was consistent with both self-report and behavioral measures of stress, giving some of the strongest evidence for appraisal theory yet reported.
Mathews and MacLeod (2002) argued that appraisals can be readily induced or changed by laboratory manipulations. Induced biases (or appraisals) affect felt anxiety when they influence how emotionally significant information is encoded by a participant. Biases and appraisals affect vulnerability to anxiety via their influence on how stimuli are processed or interpreted. Mathews and MacLeod argued that it is relatively easy to set someone up for an anxiety attack by giving him or her the right orientation toward or appraisal of up-coming events or information. The cognitive appraisal model also predicts that a person’s interpretation of an event affects the intensity of his or her reaction to it. A study by Zohar and
Brandt (2002) shows that, in cases involving a variety of possible stressful factors, the most salient stressor governs appraisal, not the summation of stressors or any other interaction of stressors. The condition perceived to be most important captures attention and takes control of how the person appraises and subsequently responds to the situation.
Anticipation of a stressful event, such as a parachute jump or piloting a plane, often includes a great deal of uncertainty. There might be a large number of unknowns, and emotions can range from extreme negative (worry, fear, anxiety) to positive (hope, eagerness, exhilaration). Skinner and Brewer (2002) studied the emotional feelings experienced during this anticipation period by students preparing for a college examination and certain other stressful events, particularly as they relate to the participants’ appraisals of the event as a challenge or a threat.
Compared to threat appraisals, challenge appraisals were associated with better emotion-coping styles, more positive emotional feelings, and greater confidence about performance. Moreover, participants who viewed the up-coming event as a
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challenge performed significantly better on that task. Because coping styles, appraisals, and emotional feelings were established in advance of the event itself, they all appear to have significant roles in mediating or determining performance.
Ennis, Kelly, Wingo, and Lambert (2001) hypothesize that subjects’ appraisal of a task or situation causes differential elicitation of neuro-endocrine activity. They determined that, if a subject sees an academic exam as a threat, sympathetic neuro-endocrine activity (measured in urine) increases before the event, relative to subjects who see the exam as a challenge. During or after the exam, activation drops and there is no difference between the threat and challenge groups in posttest measures. Overall, Ennis et al. found a positive correlation between self-reports of anxiety and adrenomedullary activity. The authors conclude, consistent with Lazarus’s model, that appraisal mediates not only behavior but also certain biological components of the human stress response.
Rohrmann, Hennig, and Netter (1999) used a different approach, but came basically to the same conclusion as Ennis et al. Rohrmann et al. demonstrated that psycho-biological reactions to the stress of public speaking can be manipulated by giving participants pre-speech information regarding how to appraise the state of their body. During an anticipation period before a speech, subjects were given either no information (in the control condition), were given information to the effect that they were psychologically aroused and nervous (in an arousal condition), or that they were psychologically calm and relaxed (in a reassurance condition). Heart rate (HR), BP, cortisol levels, and electrodermal responses were highest in the reassurance condition and lowest in the control condition. Felt emotional stress reactions, in contrast, were highest in the arousal condition and lowest in the reassurance condition. Somatic arousal was greater than felt emotion in the reassurance condition whereas felt emotion was higher than somatic arousal in the arousal condition. The authors concluded that different appraisals and consequently different coping styles were induced by pre-training. The arousal condition induced a coping style that sensitizes the subject to the state of his or her body; in contrast the reassurance condition induced a more cognitive style of stress reduction. In any case, establishing a way of appraising a potentially stressful situation mediated psycho-biological reactions to and performance during the event. Prior to a film depicting three serious factory accidents, Danboy and
Goldstein (1990) instructed some subjects about how to take and maintain a detached attitude – intellectualizing instructions – while others were merely told about the content of the up-coming film. Intellectualizing subjects demonstrated
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less self-reported stress and lower galvanic skin responses (GSRs). All subjects were less accurate on a memory test for accident related as opposed to nonaccident related aspects of the film. Thus, how you appraise the film or the events it depicts controls to some degree the emotion the film provokes, a result which is consistent with Ennis, et al. (2001) and Rohrmann, et al. (1999), although in a different context.
Larsson (1989) reported a study of the performance of Swedish military personnel on an artillery simulator, under conditions of calm, noise, and noise plus
27 hrs sleep deprivation. Apprising the task as a challenge was associated with positive coping and better performance, relative to a threat appraisal, under all conditions. But performance degraded with increased stress and negative coping increased with increased stress. Those subjects who were high in achievement motivation were more likely than those subjects who were low in achievement motivation to appraise noise and sleep deprivation as challenging and to use coping strategies that were positive and action oriented. Positive coping strategies tended to counteract the adverse effects of stress. Similar results were reported with college students by Wallbott and Scherer (1991).
Conclusions
There is a fair amount of agreement in the current literature on appraisal and stress. First, cognitive appraisals play a significant mediating role in biological reactions to stress. Second, performance outcomes depend in part on whether the subject appraises the situation as a challenge or a threat. Third, appraisals tie into coping styles such that challenges are associated with positive and more successful coping styles whereas threats are associated with negative styles. But the picture is not completely clear. It might be that, in all the experimental situations explored to date, more competent people are more likely to view any situations as a challenge rather than a threat. If this is the case, then better coping and better performance naturally follow from challenge appraisals. Because, as yet, no one has been able to create a way of separating conceptually appraisal from competence, we are left with basically a correlational result and without a clear picture of the cause-effect relationships that are involved.
Attention and Perception
It is clear that stress, especially acute stress, has important effects on attention and perception. But the effects are quite irregular, and depend in serious ways on the qualitative features of the stressor. Different stressors have different effects on performance. One stressor might cause shifts in attention or a failure to inhibit irrelevant stimuli, while another stressor causes a lapse of attention or attentional narrowing in the same task.
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Inhibition and Attention
Given that the effects of stress on attention can be unpredictable, still there are some results that are general, systematic, and reliable. One example is the latent inhibition (LI) effect. Pre-exposure to a stimulus reduces the utilization and the learning of that stimulus on some later occasion. This LI phenomenon is typically attributed to a reduction in attention to stimuli caused by their preexposure in another task. When stress is present in the learning or test phase, however, latent inhibition is reduced or eliminated. Attention to the stimulus is not affected by pre-exposure and learning involving the pre-exposed stimulus is as good as if the stimulus was novel. Stress was induced in one experiment
(Braunstein-Bercovitz, Dimentman-Ashkenazi, & Lubow, 2001) by threats to selfesteem in a difficult number series completion test said to be related to intelligence. In a second case studied by the same authors, the LI task was described as a part of the selection process to job seekers. LI was attenuated in both experiments in high as opposed to low stressed subjects. Thus the results show that stress impairs the inhibition of irrelevant pre-exposed stimuli.
Is proneness to anxiety associated with impaired inhibitory processing?
Participants in a series of experiments reported by Wood, Mathews, and Dalgleish
(2001) made speeded decisions which required inhibition of the meaning
(threatening or neutral) of ambiguous words. Under normal conditions, they found that anxious and non-anxious participants perform equally well in this task.
However, when a mental load was induced to reduce controlled processing, anxious subjects did not inhibit word meaning as well as non-anxious subjects. In a final experiment, attenuation of inhibition was demonstrated even without mental load in subjects who had recently experienced a traumatic event.
Keinan, Friedland, Kahneman, and Roth (1999) reported similar stress effects with both college students and navy personnel using a variety of cognitive tasks, including arithmetic, estimation, number series, and analogies. In the number series and analogies tasks, both of which required the inhibition of competing responses, but not in the other tasks, performance was poorer in the high than in the low stress condition. These authors concluded that stress heightens the difficulty of suppressing or filtering out competing responses.
Mogg, Bradley, and Hallowell (1994) tested high and low trait anxious students for attentional bias to threat stimuli (words) under no stress, laboratoryinduced stress, and natural examination-induced stress. High anxious subject
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showed an attentional bias toward threat words, but only when those words were presented for long duration, without a mask, and under examination threat.
Anxiety sensitized the subject to threat mainly when the induced anxiety is somewhat protracted.
Measured levels of stress hormones are consistent with the abovedemonstrated effects of stress on inhibitory processes. Skosnik, Chatterton,
Swisher, and Park (2000) induced mild stress into the verbal priming paradigm using a video game. Stress reduced negative priming, a measure of inhibition processes, and also increased salivary cortisol and alpha-amylase (a correlate of norepinephrine). So, both chronic anxiety, as in trait anxious subjects, or acute anxiety, as in trauma, is associated with a general deficit in inhibition of attention, and is best revealed when limitations are placed on controlled processing, forcing subjects to rely more heavily on automatic reactions. Behavioral and physiological measures are consistent with changes induced by stress on inhibitory processes. These results imply that, in a natural emergency, when stress is high, there is need to be concerned about an operator’s ability to focus on the relevant information in the task at hand and to inhibit irrelevant sources of input.
Perception and Cue Utilization
Based on a review of the early literature on arousal and attention,
Easterbrook (1959) concluded that stress, anxiety, or high arousal can narrow the range of environmental cues utilized, shrinking one’ effective perceptual space.
This idea has been expanded by Cowan (1999) in a theoretical analysis of working memory. Among other things, Cowan draws a sharp distinction between attentional processes, which in his view are basically capacity-limited, and working memory, (the activated portion of long-term memory in his theory), which is basically time-limited. Thus, consistent with Easterbrook, Cowan predicts that the effects of stress on attention are to limit its scope or content. People attend to and process less perceptually-available information when they are stressed. In contrast, the effects of stress on memory are to limit its time extension. Such an expectation is consistent with the memory constriction hypothesis that we develop in this report. Since Easterbrook’s publication, there have been numerous demonstrations of an attentional deficit under stress, in and outside of the laboratory. For example, Ozel (2001) found that time pressure and the stress created by the threat of fire affects how people process information provided to them about the right route to take to escape. Slight stress was beneficial to escape
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performance, but higher levels of stress narrowed the range of environmental cues attended to or processed and increased the use of negative coping styles by participants. Escape performance suffered as a consequence.
Vigilance
Performance in a vigilance task, which requires the detection of infrequent stimuli, degrades in time, a phenomenon known at the vigilance decrement (Mackworth, 1950). Galinsky, Rosa, Warm, and Dember (1993) observed that restlessness and subjective fatigue, both indices of stress, increased dramatically across a 50-min watch in a vigilance task in which sensory modality of signals (audition and vision) and the background event rate (5 and 40 events/min) were varied. Stress effects were most notable in the case of visual monitoring but were unrelated to variations in event rate. Thus, the stress of sustained attention seems to be identified more specifically with the sensory modality of signals than with the event rate context in which they appear. Temple, Warm, Dember, Jones,
LaGrange, and Matthews (2000) observed that 30 mins or more of sustained vigilance produces not only a performance decrement, but also increases in felt workload and stress. Stimulant drugs, like amphetamine sulphate or caffeine, extraneous auditory stimuli, and other arousing agents should enhance vigilance and counteract the deterioration in vigilance performance that occurs with the passage of time. Temple et al. (2000) found evidence that ingestion of caffeine during the task improved vigilance and signal detection but did not reduce task-induced stress.
Lavine, Sibert, Gokturk, and Dickens (2002) examined concurrent eye movements and human performance during a vigilance task designed to require frequent visual scanning. Stimuli were 4 digits in a rectangular array, changed at an event rate of 4 s for a task duration of 30 min. Participants were asked to respond to specific, infrequent signal arrays by bar press, under both 50 dBA white noise and
90 dBA intermittent and unpredictable sound-burst conditions (SBC). With timeon-task, subjective fatigue ratings increased, the total duration of fixations on target digits decreased, number of fixations decreased, and fixations were further from target digits in both conditions. Thus, the usual vigilance performance decrement was replicated. Fixation duration did not change significantly with time or condition. Off-target visual scan-paths were less frequently followed by hits than were on-target scan-paths in both conditions. With the SBC, fixations were closer to target digits and hit rates increased, suggesting that background stimuli with a potential alerting function can help to offset the vigilance decrement.
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Conclusions
Both chronic anxiety, as in trait anxious subjects, or acute anxiety, as in trauma, produce a general deficit in a person’s ability to inhibit irrelevant stimuli. The effect is most clearly revealed when limitations are placed on controlled processing, forcing subjects to rely more heavily on automatic reactions. These results imply that, in a natural emergency, when stress is high, there is need to be concerned about an operator’s ability to focus on the relevant information in the task at hand and to inhibit irrelevant sources of input. This effect of stress on inhibitory processes is similar to and likely related to Easterbrook’s finding that the range of cues perceived and attended to shrinks under stress or high arousal. Other evidence shows that the ingestion of stimulants can be effective in offsetting the vigilance decrement as can the aperiodic occurrence of irrelevant or background stimuli, if they have some degree of alerting function.
Memory
. As we have noted earlier, cognitive psychology is currently concerned with a variety of forms of memory. One important distinction applies to the temporal character of information retrieved from memory. This distinction is based on a continuum from the remote past – retrospective long term memory – to the present or near present – short term memory and immediate or working memory – to the future – prospective memory. Long-term memory is theoretically a repository for facts and skills acquired in the past. Short term and immediate memory holds facts and skills that are currently at the focus of attention.
Prospective memory contains reminders of actions to be executed at some future time and place. The important variables influencing memory might not the same in all three cases. One variable that seems likely to be influential is stress.
Stress effects have been studied in the context of various forms of memory, although the experimental data available are surprisingly few. There are no data comparing different forms of memory for their relative susceptibility to stress. The evidence that is available seems to suggest that stress, in general (including stress arising in emergency situations), causes the operator to focus on the here-and-now, with consequent potential degradation of retrospective and prospective memory performance. The results are consistent with a memory constriction or tunneling hypothesis to the effect that the time span from which knowledge can easily be retrieved and used in a given context shrinks as stress level increases. Neglect of facts or procedures in long term memory, and failure to execute required behaviors at appointed future times is a major reason for performance errors or failures in emergencies. Although memory tunneling has been observed in the retrieval of autobiographical events (Berntsen, 2002), empirical evidence to support this broad
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stress/memory hypothesis is weak. The hypothesis could, however, serve a framework for future research efforts.
General Stress Effects on Memory.
As we have shown in other sections of this report, a variety of stressful conditions impede a variety of memory measures. For example, Gomes, MartinhoPimenta, and Castelo-Branco (1999) showed a significant impact of stressful noise on immediate verbal memory. Fowler, Prlic, and Brabant, (1994) reported a similar effect of hypoxia on the executive function of working memory. Mandler
(1979) was one of the first cognitive psychologists to speculate theoretically about the effects of stress on memory. Stress produces noise in the cognitive system, according to Mandler, which competes with task demands for limited cognitive, that is, conscious resources. Recall that a similar proposition about noise in the cognitive system, generated by stress, was made by Van Gemmert and Van Galen
(1997). Thus, in Mandler’s theory, those memory processes that rely on conscious elaboration of input and representations, namely explicit memory processes, should be especially degraded by stress. To date, there has been no clear test of this hypothesis. It is not inconsistent, however, with the memory constriction
(tunneling) hypothesis describe earlier, in the sense that focusing on the here and now necessarily requires explicit memory while longer term recall and prospective recall might not.
As we shall discuss in detail later, Van Overschelde and Healy (2001) have shown empirically that one mechanism for coping with and reducing the stress that information overload engenders is to provide connections between new facts to be learned under stress and an existing knowledge base. The general principle is that the acquisition and retention of new, factual information is facilitated whenever that new information can be linked to existing knowledge. The mechanism underlying this strategic-use-of-knowledge principle is based on the provision of a retrieval strategy supported by factual information that already exists in long-term memory. This idea is an extension of the theory of long-term working memory
(Ericsson & Kintsch, 1995), which has been used, for example, to account for text comprehension and for expert-level performance in memory-span tasks. This is still another hypothesis that should be testable empirically, although it has not been examined in the literature to our knowledge.
Another approach to the role of working memory in the explanation of stress effects is represented by the work of Ashcraft (2002; see also Ashcraft & Kirk,
2001). People with high math anxiety have a reduced working memory capacity
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according to Ashcraft. Because working memory is required by many arithmetic and mathematical tasks, math anxious subjects perform more poorly on these tasks than low anxious subjects. This leads to the prediction that, if working memory can be limited artificially in non-anxious subjects, their performance on calculation tasks should similarly be adversely affected. By introducing a concurrent task with working memory demands or by stretching working memory by primary task demands, Ashcraft was able to show effects on performance similar to those observed in high math anxious subjects. Ashcraft’s conclusion is that stress exerts its effects primarily by reducing a person’s working memory capacity. Such a result, if replicable, might be inconsistent with the memory constriction hypothesis, described above, in the sense that memory constriction implies a greater effect of stress on retrospective and prospective memory than on working memory. Studies comparing various forms of memory under stress are needed to decide between these hypotheses. Any task that requires explicit learning and/or memory processes should be especially liable to stress effects, according to Ashcraft.
Conclusions similar to those of Ashcraft have been reached by Eysenck
(1992, 1997; see also Eysenck & Calvo, 1992). Moreover, in a recent review of research on working memory, Miyake and Shah (1999) identified emotion, stress, and especially anxiety as a major modulating factor of working memory capacity.
They suggest that, in various ways, stress limits the time scope of memory. But, after searching the literature, they concluded that insufficient empirical data have been collected on the problem and recommended further research to identify what aspects of working memory (e.g., maintenance, executive control, content) are influenced by anxiety and other emotional factors. Why should working memory capacity be reduced under stress? Matthews (1996) argues that “worries,” daily hassles, and/or intrusive thoughts tend to occupy more space in working memory among high anxious than among low anxious subjects, limiting the available working memory space in high anxious subjects for the calculations that their primary task requires (see also Dudke & Stoebber, 2001). There is some evidence that a stressful event, itself, can cause lingering intrusive thoughts (see below), but little data at present to support Matthews’s “worries” hypothesis.
A caution. Studies of stress and memory must take account of state and context dependency effects. That is, it has routinely been shown that performance in a retention test is better if the state of the subject and/or the context in which the test is administered are the same as the state and context of original learning.
Although stress might exert adverse effects on both encoding and retrieval processes, there is some possibility that changing the stress state of the organism between the times of learning and retention, from stress to no stress or from no
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stress to stress, will have its own adverse consequences. But, other things being equal, recall performance will be better if tested under the same state, stress or non-stress, as present during encoding. Lang, Craske, Brown, and Ghaneian,
(2001) demonstrated this phenomenon in a word recall task using induced states of both fear and relaxation. But, most studies of stress and memory in the current literature ignore these dependencies, usually testing the subjects’ memory under stress for information or skill acquired under non-stressful circumstances. This is a serious limitation on the usefulness of the current stress/memory literature, and must be corrected in future work.
Memory for emotion-arousing stimuli. There is conflicting evidence in the literature regarding memory for emotionally arousing stimuli. As we noted earlier, most studies have reported that memory is better for either pleasant or unpleasant material than it is for emotionally neutral material. But there are exceptions.
Further, some investigations have, reported that traumatic stimuli, like autopsy photos, can inhibit memory for simultaneously presented neutral material (see, e.g.,
Kramer Buckhout, Fox, Widman, et al, 1991). Whether these differential observations should be attributed to differing methods of presenting materials and measuring memory or to the degree of emotion provoked by the stimulus material is not clear at the present time.
Lang, Davis, and Ohman (2000) attempted to explicate what is special about memory for emotional information, emphasizing the neural foundations that underlie the experience and expression of fear. They proposed that unpleasant emotions depend on the activation of an evolutionarily primitive subcortical circuit, including the amygdala and the neural structures to which it projects. This motivational system mediates specific autonomic (e.g., HR change) and somatic reflexes (e.g., startle response) that originally promoted survival in dangerous conditions. These authors show how variations in the neural circuit and its outputs may separately characterize cue-specific fear (as in specific phobia) and more generalized anxiety. Emphasizing links between animal and human data, these authors focus on certain special, attentional features of emotional processing, including: (1) The automaticity of fear reactions, (2) hyper-reactivity to minimal threat-cues, and (3) evidence that the physiological responses in fear are independent of slower, deliberate language-based appraisal processes. This last difference accounts, in their view, for the special character of and better memory for emotional as contrasted with neutral information.
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Cortisol and other Neuro-biological Considerations..
Cortisol is a stress hormone that readies the body to fight or for flight.
Among other things, cortisol stimulates the secretion of intracellular glucose into the blood, which allows longer and more vigorous and sustained responding.
Although the mechanism is less clear, it is also known that ambient cortisol levels can affect cognition. For example, al’Absi, Hugdahl, and Lovallo (2002) showed that participants who had a large cortisol responses, i.e., acutely elevated levels of cortisol, during mental arithmetic and public speaking tasks, performed better 30 mins later on a dichotic listening task, compared to those who had low cortisol responses. Dichotic listening requires sustained focused attention to external stimuli, and sustained attention is known to engage the executive processes of working memory. Thus, it is of great interest that working memory depends on adequate functioning of the dorsolateral prefrontal cortex (Smith & Jonides, 1999), an area richly supplied with corticosteroid receptors and corticotropin-releasing factor terminals. It has been argued that these studies imply that emotional dispositions, possibly even more than environmental circumstances, are crucial in how one responds behaviorally to stress (Kosslyn, Cacioppo, Davidson, Hugdahl,
Lovallo, Spiegel, & Rose, 2002).
As noted above, there is evidence that stress has effects on both encoding of new memories and retreival of old memories. But what about memory storage, the process of holding memories after encoding for later use in retrieval tests? For several decades, the concept of modulation of storage has significantly influenced research investigating neurobiological memory mechanisms in animals. New evidence provides additional support for the view that stress hormones released during emotionally arousing situations can influence memory storage. Recent experiments have investigated the role of sympathetic adrenomedullary hormones in emotional memory in human beings, as well as the role of adrenocortical hormones, primarily in animal studies. Further, it is becoming increasingly clear that the sympathetic adrenomedullary and the pituitary adrenocortical systems interact to modulate memory storage. Other new evidence emphasizes the role of peripheral influences to the brain on emotional memory, as well as the critical contribution of the amygdaloid complex in modulation of memory by emotional arousal. For a review of this literature, see Cahill and McGaugh (1996).
Glucocorticoids (GCs), produced by the stress-responsive hypothalamicpituitary-adrenal axis, are well recognized for their regulatory role in peripheral metabolism. But GCs are also known to regulate various brain functions, involved in human cognition (Cahill & McGaugh, 1996). Increased GC exposure in human
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beings at levels associated with stress has most often been found to decrease memory and learning function (see below). Evidence of these effects in adult human beings and animals has been reviewed by Hefflinger and Newcomer
(2001). As an aside, these authors pointed out that less is know about cortisol and memory in children and older people than in adolescents and adults. But Cahill and McGaugh (1996) have speculated that cortisol levels can, in some circumstances, enhance memory function. Buchanan and Lovallo (2001) attempted to test this idea and to extend findings with animals to human memory performance. Following administration of cortisol or placebo, college aged participants were exposed to pictures varying in emotional arousal. Incidental memory for the pictures was assessed one week later. Results showed that elevated cortisol levels during memory encoding enhanced the long-term recall performance of emotionally arousing pictures relative to neutral pictures. It is not clear why cortisol should selectively support memory for emotion provoking stimuli. But in general the results suggest that cortisol secretion can have beneficial cognitive effects in some circumstances. Note that Buchanan and Lovallo failed to control for state dependency, which once again prevents a clear interpretation of the role of stress (or cortisol) in encoding vs. retrieval processes.
Most of the recent literature with human subjects is not consistent with the results of Buchanan and Lovallo (2001), and more in line with the adverse effects of elevanted cortisol claimed by Hefflinger and Newcomer (2001). For example,
Kirschbaum, Wolf, May, Wippich, et al. (1996) reported two experiments on the association between cortisol levels and memory in healthy human adults. In the first study, subjects were exposed to the Trier Social Stress Test with a subsequent test of declarative memory performance. Results indicated a significant negative relationship between stress-induced cortisol levels and performance in the memory task. The second experiment investigated whether cortisol alone, independent of psychological stress, would also impair memory function. Male Ss received either
10 mg cortisol or a placebo orally. One hour later they were tested for procedural and declarative memory and spatial thinking. Subjects who received cortisol showed impaired performance in the explicit declarative memory and spatial thinking tasks although not in the implicit procedural memory task. Accordingly, their results suggest that, in healthy adults, elevated free cortisol levels may be associated with impaired explicit memory function, that is, functions that require conscious awareness and an important role for working memory, but not functions that operate automatically.
Wolf, Schommer, Hellhammer, McEwen, Kirchbaum, (2001)) reviewed epidemiological and experimental studies and found that elderly subjects are
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especially susceptible to memory impairing effects of elevated cortisol levels, postmenopausal women more so than elderly men. They noted further that, on the whole, little is known about gender differences in susceptibility to acute stress in young subjects. Therefore,Wolf at al (2001) conducted a study of healthy college students who learned a word list, with recall being tested after a brief distraction task. Some of their subjects learned the list after exposure to a psychosocial stressor, while the remaining subjects served as controls. Free cortisol was determined via saliva samples taken before and 10 mins after stress. Subjects exposed to the stressor, did not show impaired memory performance per se when compared to the control group. However the size of the cortisol increase in response to the stressor was negatively correlated with the memory performance within the stressed group (i.e., subjects showing a larger cortisol response recalled fewer words than subjects showing only a small cortisol increase). Additional analysis by Wolf et al. (2001) revealed that this correlation was high in men and nonexistent in women. The data suggest that gender might modulate the association between cortisol and memory after stress.
Newcomer, Selke, Melson, Hershey, Craft, Richards, and Alderson, (1999) reported an experiment in which participants were given 1 of 2 oral hydrocortisone doses or a placebo. Paragraph recall was used as a measure of verbal declarative memory. Results indicate that several days of exposure to cortisol at doses and plasma concentrations associated with physical and psychological stress in human beings decreases verbal declarative memory function in otherwise healthy human beings. A nother r elated r esult w as r eported b y Vedhara, H yde, Gilchrist,
Tytherleigh, and Plummer, (2000), who conducted an investigation to explore the relationship between acute changes in cortisol and memory and attention in the context of an acute naturalistic stressor, namely, examination stress in college students. Assessments of self-reported levels of stress, salivary cortisol, short term memory, selective and divided attention, and auditory verbal working memory were conducted during a non-exam and an exam period. The results revealed that the exam period was associated with an increase in perceived levels of stress, but also a significant reduction in levels of salivary cortisol, compared with the non-exam period. This reduction in cortisol was associated with enhanced short-term memory (as measured by the total number of words recalled in a free recall task), impaired attention and an impairment in the primacy effect (a hippocampal-specific index of short term memory), but no significant effects on auditory verbal working memory.
Further confusing the picture is a study reported by Lupien, Gillin, and
Hauger (1999) who measured the effects of various doses of hydrocortisone on
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performance in tasks assessing working and declarative memory function. During the infusion period, participants were given an item-recognition working memory task, a paired-associate declarative memory task, and a continuous performance task used to control possible concomitant effects of corticosteroids on vigilance.
The results revealed significant acute degrading effects of the highest dose of hydrocortisone on working memory function, without any significant effect on declarative memory function or arousal-vigilance performance. These results suggest that working memory is more sensitive than declarative memory to the acute elevations of corticosteroids, which could explain the detrimental effects of corticosteroids on acquisition and consolidation of information, sometimes reported in the literature (Cahill & McGaugh, 1996). Taken as a whole, the available data support the unsatisfactory conclusion that cortisol modulates cognitive processes, but in a highly selective manner
The results of Wolf et al., Vedhara et al, Newcomer et al., and Lupien et al. all appear to be inconsistent with Buchanan and Lovallo’s finding of cortisol support for retrospective memory of emotion-arousing stimuli. More data will be required to reconcile this discrepancy. Of course, one possible explanation is that various researchers induced or measured cortisol levels at different points on the
Yerkes-Dodson function. Thus, Buchanan and Lovallo’s data might to attributable to a relatively low cortisol level in their subjects, thereby facilitating performance on the upward rise of the Y-D function, while other researchers induced or measured higher levels of cortisol, beyond the optimum on the Y-D function.
More than anything else, this possibility demonstrates how slippery the issue is and how the Y-D principle can be used to explain almost any outcome. Further complicating the picture is the fact that none of these experiments took account of possible state dependency effects. Thus it remains unclear whether the effects of elevated cortisol levels, whether facilitative or adverse, are the same on encoding and retrieval processes in memory.
According to de Kloet, Oitzl, and Joëls (1999), some of the discrepancies reported in the memory literature as regards the role of corticosteroid hormones might be explained by appealing to the specific role of both mineralocorticoid and
GC receptors in the various stages of information processing. Corticosteroid effects on cognition can turn from adaptive into maladaptive when actions via the two corticosteroid-receptor types are imbalanced for a prolonged period of time. But before we should accept the de Kloet et al. claim, or any other possibility that relies on biological explanation, experiments with proper control and manipulation of cortisol levels and state dependencies in encoding and retrieval will need to be conducted and reported.
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Context and State Dependency involving Stress.
One of very few studies to take account of state and context dependency effects in memory was conducted by Thompson, Williams, L 'Esperance, and
Cornelius (2001). In the first of two experiments, experienced skydivers learned word lists prior to skydiving either in the air or on the ground and recalled them in the same context or in the other context. The second experiment was a replication of the first except that participants were shown a skydiving video in lieu of actual skydiving. Recall was poor in air-learning conditions with actual skydiving, whether learning took place in the air or on the ground. But when lists were learned on land, recall was higher in the matching context than in the mismatching context. In the skydiving video experiment, recall was higher in matching learnrecall contexts regardless of the situation in which learning occurred. It is proposed then that under extremely emotionally arousing circumstances, environmental and/or mood cues are unlikely to become encoded or linked to newly acquired information and thus cannot serve as cues to retrieval. Context and state dependency effects are real, but might be overridden when emotions are extreme.
Results can be applied to understanding variations in context-dependent memory in occupations in which the worker experiences considerable emotional stress while learning or recalling new information. But the main point is that these dependency effects must to be taken into account in all future experiments purporting to study stress and memory.
Other Considerations
False memories. Payne, Nadel, Allen, Thomas, and Jacobs (2002) demonstrated that stress can enhance a person’s susceptibility to false memories.
In a recall task, participants ' ability to distinguish words that were presented for study from critical lure words that were semantically related, but not presented for study, was selectively disrupted. This finding indicates that stress potentiates false memories. An argument was made by the authors that this effect is mediated through the impact of stress on the hippocampus and prefrontal cortex, but this interpretation is an extreme extrapolation from the data, which contained no measurements of brain activity.
Intrusive thoughts. Not only does stress affect and often limit memory, but also memories of stressful events can provide a basis for intrusive thoughts, resulting in persistent, protracted, lingering, or chronic stress – a kind of vicious circle (Baum, Cohen, & Hall, M, 1993). Intrusive thoughts have been identified as
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key elements in chronic or traumatic stress and the post-traumatic stress syndrome, but many questions remain about how they operate and what causes their persistence over time. Schooler, Dougall, and Baum (1999) considered these questions, examining the impact of having intrusive thoughts that are cued by stimuli in one 's environment as opposed to non-cued intrusions that seem to "come out of the blue." This research evaluated the extent to which distress accompanying intrusive thoughts shortly after a traumatic event predicts persistence of intrusions over time. Rescue workers who responded to the crash of Flight 427 were studied
4-8 weeks, and 6, 9, and 12 months after the disaster. Participants who reported crash-related thoughts that were not prompted by cues showed higher levels of distress than those reporting only cued thoughts or those reporting neither. The magnitude of distress that these non-cued thoughts caused in the first 2 months after the crash was important in predicting subsequent frequency of unwanted thoughts. Matthews (1996) has argued that intrusive thoughts and other “worries” occupy space in working memory, thus limiting performance in tasks that rely on working memory. But, at this time, no one has reported any solid evidence to support the detrimental effects of intrusive thoughts, whether cued or non-cued, on subsequent cognitive task performance.
A Memory Constriction Hypothesis
As noted earlier, one important distinction in contemporary memory research and theory applies to the temporal focus of information to be retrieved from memory and used. This distinction is based on a continuum from the remote past – retrospective long term memory – to the present or near present – short term memory and immediate or working memory – to the future – prospective memory.
The effects of important variables, including stress variables, might not be the same in all of these cases. Somewhat surprisingly, the data available on possible differences are surprisingly skimpy. Moreover, there are few systematic studies of stress on memory over a wide range of stress values. To our knowledge, there are no direct comparisons of retrospective, working, and prospective memory under stress. What evidence is available seems to suggest that stress typically causes the performer to focus on the here-and-now, with consequent degradation in retrospective and prospective memory. The results are consistent with a memory constriction or tunneling (Bernsten, 2002) hypothesis to the effect that the time span from which knowledge can easily be retrieved and used in a given context shrinks as stress level increases. Neglect of facts or procedures in long term memory, and failure to execute required behaviors at appointed future times might be a major reason for performance errors or failures in emergencies. Unfortunately,
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at the present time, empirical evidence to support this hypothesis is nonexistent.
The hypothesis could, however, serve as a framework for future research efforts.
Conclusions
A variety of stressful conditions affect a variety of memory measures, usually but not always in an adverse way. Mandler was one of the first cognitive psychologists to theorize about these effects, attributing them to cognitive resource limitations and to stress-produced noise in the cognitive system. People with high math anxiety have a reduced working memory capacity and, because working memory is required by many arithmetic and mathematical tasks, math anxious subjects perform more poorly on these tasks than low anxious subjects. There is conflicting evidence in the literature regarding memory for emotionally arousing stimuli. Many studies have reported that memory is better for either pleasant or unpleasant material than it is for emotionally neutral material. But there is some evidence that traumatic stimuli can inhibit memory for simultaneously presented neutral material.
There is extensive evidence that cortisol level is correlated with memory. But sometimes elevated cortisol levels have been shown to have a positive effect and sometimes a negative effect on memory. One possible explanation is that various researchers induced or measured cortisol levels at different points on the Yerkes-Dodson function. Further complicating the picture is the fact that few stress/memory experiments have taken account of possible state dependency effects. Thus it is unclear whether the effects of elevated cortisol levels, whether facilitative or adverse, are the same on encoding and retrieval processes in memory.
Not only does stress affect and often limit memory, but also memories of stressful events can provide a basis for intrusive thoughts, resulting in persistent, protracted, lingering, or chronic stress – a kind of vicious circle. To date, no one has reported on the possible detrimental effects of intrusive thoughts on cognitive task performance.
Environmental Conditions that Induce Stress
Time Pressure
One of the most obvious ways to put a performer under stress is to impose time limitations on the task or to give frequent “hurry up signals.” Intuitively, most people feel that they do not do their best work under time pressure, although there might be important individual differences in this regard. It is surprising therefore to discover that the literature contains very little evidence on the effects of time pressure on cognitive performance. Moreover, those studies that have been reported find rather obvious and uninteresting results.
The task used by Van Galen and van Huygevoort (2000) required subjects to make cursor movements to targets varying in width and distance. On the basis of
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the theory of van Ghemmert and Van Galen (1997), which has been described elsewhere, the authors tested the prediction that time pressure and dual task load would influence error rates and movement variability, together resulting in biomechanical adaptations of pressure on the cursor control. The latter is seen as a manifestation of a filtering strategy to cope with increased neuromotor noise levels. The results confirmed that, especially under time pressure, error rates and movement variability were enhanced, while cursor control pressure was higher in both conditions of stress.
Ashcraft (2002) has demonstrated that the performance decrement suffered by math anxious subjects on quantitative problem solving is in part attributable to a compromised working memory. In an extension of this idea, Kellogg, Hopko, and
Ashcraft (1999), following Matthews (1996), tested whether the limitation of working memory observed in anxious subjects might be the result of worry, i.e., that their consciousness is occupied to some extent by concern over the likelihood of poor performance. Time pressure could be a factor contributing to worry and thus to the poorer performance of anxious subjects. These researchers found, however, contrary to the worry hypothesis, that time pressure lowered performance of both anxious and non-anxious subjects equally. Thus the worry resource model was not supported by their data.
When response time deadlines are imposed in quantitative tasks, such as addition or multiplication, performers often adopt a strategy that is different from the one they would use in normal circumstances. Typically, these adopted strategies place less of a demand on working memory. For example, Campbell and
Austin (2002) showed that adult subjects shifted from a calculation-based or procedural strategy to a direct memory retrieval strategy to perform mental addition problems when they were put under time pressure. Performance suffered as a consequence of this shift, especially in more difficult problems
Entin and Serfaty (1990) reported an experiment to investigate the effects of time pressure on decision-making. Their paradigm involved a single decision maker whose job was to classify submarine sonar returns as coming from a friendly or enemy boat, on the basis of differences in average pump noise frequency between the two classes. After being given the value of the unknown submarine 's measured pump frequency, the subject either classified the submarine as friend or foe or, for a cost, asked for more information. This information was chosen to be either another raw measurement (probe) or the opinion of an automated consultant. Two distinct subject populations were used, civilian
(engineering firm employees and college students) and military. For both groups,
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performance under time pressure was significantly poorer than normal. The effects of time pressure are, then, what one would intuitively expect them to be. The researchers provided no speculation as to the underlying processes that might be engaged by time pressure and how they operated to affect performance.
Furthermore, because only two conditions were used, the experiment yields no evidence on the shape of the function between performance and time pressure.
Two person command and control teams were trained, in an experiment reported by Lehner, Seyed-Solorforough, O 'Connor, Sak, and Mullin (1997), to make decisions using a prescribed strategy following a set of simple decision procedures. The authors were interested in the impact of time stress on the decision-making performance of teams. The results supported the conclusion that prescribed decision procedures, which were somewhat counter-intuitive, would be more vulnerable to the effects of time stress than other more familiar and intuitive decision procedures. In addition, the results suggested that the subjects adapted inappropriately to time stress. As time stress increased, they began to use a decision processing strategy that was less effective than the strategy they were trained to use, reverting to procedures that were more familiar to them. While this study focuses on team performance, there is nothing in the data to suggest that same results would not be obtained with individuals working alone.
A study by Ozel (2001) provides greater insight into the effects that time pressure can have on fundamental cognitive processes. Ozel examined the manner in which stress, created by the threat of fire, affects how people process information provided to them about the correct escape route. Ozel reported that modest stress was beneficial to performance, but that extreme time pressure impeded performance by narrowing the range of environmental cues attended to or processed, an outcome predicted by Easterbrook (1959). In addition, the use of negative coping styles increased with time pressure.
Work Load and Overload
It is difficult, for reasons mentioned elsewhere in this review, to create extreme or prolonged conditions of stress in the laboratory. Laboratory studies generally focus on relatively weak acute stress. An example involves adding workload or secondary task requirements to a primary or focal task. Subjects often find these additions to be stressful at least at the outset and they can adversely affect primary task performance. Given some experience or practice, however, individuals can often find ways to accommodate to the greater demands of doing two things at once.
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Consider the work of Matthews, Sparkes, and Bygrave, (1996), who tested the hypothesis that driver stress is associated with performance impairment mainly because stress-prone drivers are vulnerable to overload of attentional resources. In other words, those who are susceptible to the effects of stress suffer from limitations on attentional resources and are more distractible by irrelevant nondriving events. Young subjects performed a simulated drive concurrently with a grammatical reasoning task, presented either visually or auditorily. In this experiment, the patterns of dual-task interference predicted by attentional resource theory were actually not found, although some interference was apparent with the auditory reasoning task. Measures of vulnerability to driver stress and intrusive cognitions were related to impaired lateral control of the vehicle mainly when task demands were relatively low, contrary to the overload hypothesis. These data indicate that performance in this task paradigm is characterized by adaptive mobilization of effort to meet changing task demands. Stressed drivers adapted to high levels of demand fairly efficiently. The levels of stress involved here obviously fall within the range that can be compensated for by strain or mobilization. But, in contrast, Metzger and Parasuraman, (2001) found that, at higher levels of overload, created by a secondary task during driving in high traffic density and assessed by HR and self-report measures, performance does gradually but significantly decline. Parallel results were reported by Zeier (1994) for air traffic controllers.
With practice, people often find ways to incorporate secondary task requirements into the strategy they use to perform the primary task. Healy,
Wohldmann, Parker, and Bourne (submitted), for example, recently reported evidence of this phenomenon in a series of experiments on time estimation. Two groups of subjects were trained on a time estimation task under stress created by various secondary tasks. One secondary task was relatively easy, requiring the repeated articulation of a given letter of the alphabet. The other secondary task was quite difficult, requiring recitation of the alphabet backward by three 's starting with a given letter. Performance in these conditions was compared to that of a third, control group, trained without the stress of a secondary task. Training led to improvements in performance in all three conditions but training with the difficult secondary task degraded, or strained, performance considerably relative to the other two conditions. Importantly, removing the secondary tasks after training in a transfer task actually impaired performance for those subjects trained with either secondary task relative to the control. In fact, performance was worse after training for subjects in the difficult secondary task condition than it was at the beginning of training for subjects in the control condition. This is a surprising and
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unique finding with crucial implications both for training and for understanding workload and stress effects. It is consistent with the procedural reinstatement principle proposed by Healy and Bourne (1995) if it is assumed that the procedures used by subjects to estimate time somehow accommodated the requirements of the specific secondary task. The idea is that when the secondary task is removed in the transfer session, new procedures are required to perform the primary task alone, leading to an initial performance decrement.
The results of this study raise an interesting empirical question about training to contend with stressors. Training may be specific to the particular stressor or stressors that are present during practice. The procedural reinstatement principle implies that training with one stressor will not necessarily generalize to test conditions (i.e., to retention, transfer, or retraining) under other stressors. For example, training under the stress of time pressure to respond may enhance subsequent performance under another type of time pressure, but may not adequately prepare individuals for subsequent performance under conditions of fatigue or work overload. In fact, training under time pressure may put a person at a disadvantage when tested under different adverse conditions. The results of
Matthews et al. (1996), who studied driving under various stress conditions are consistent, although not definitive, with respect to this expectation. Training under two or more adverse conditions may support wider generalization at test even when the adverse conditions at training do not match those at testing, in agreement with a variability of practice hypothesis of Schmidt and Bjork (1992). What actually happens, of course, is an important empirical question that needs to be addressed at some point in this project.
Information overload threatens our limited cognitive capacity and can quickly degrade performance in many daily tasks (for the classic argument, see
Miller, 1956). Fitts (1966), for example, demonstrated that an overload condition created by time pressures significantly increased error rates in a complex reaction time task. Under circumstances of high information load, artificial memory aids can be especially beneficial to performance. In most experiments that have examined time pressure, the decline in performance is gradual rather than catastrophic, as would be case if cognition was completely overwhelmed. As an example of how this works, consider a recent series of experiments by Burrows
(2002) that examined how workload variables such as amount of information, speed of information presentation, and secondary task requirements, interact to create a condition of overload and how they influence recognition memory.
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Burrows (2002) measured the recognition of previously presented words, with the length of the memory list increasing with each presentation. Gradual declines in recognition performance were observed over trials (and with expanding lists). It is important to note that performance degradation was gradual, rather than abrupt. Subjects were able to adjust to conditions of overload by maintaining in memory some significant portion of the materials to be retained. When rate of information presentation was increased, performance was adversely affected, but the slope of degradation function associated with increasing the size of the memory list was not changed. That is, recognition memory decreased gradually as the size of the list increased and as the rate of presentation increased, but these variables did not interact. In one final experiment, Burrows required his subjects to perform a second task simultaneous with recognition memory. Several new items were added to the memory list on each successive trial, and, in addition, subjects were instructed to forget or eliminate a small subset of earlier items. Thus, each memory trial required not only adding new items but also deleting others and a reorganization of the remaining memory list. The requirement to delete and reorganize in memory degraded overall performance. The effects were entirely attributable to mishandling the deleted items. That is, performance on retained and added items was the same in the standard learning condition. But subjects were completely incapable of retaining the current status of deleted items, sometimes recalling them as part of the list and sometimes not.
Burrows’s studies suggest two major conclusions regarding the workload placed on memory. First, expanding the length of a list to be remembered causes a gradual (non-catastrophic) decrease in performance. Second, the requirement to reorganize an expanding list does result in an abrupt decline in performance mainly attributable to a complete forgetting of the status of deleted items. The practical implications of these results are likewise two-fold. First, when new information is periodically introduced into a task, modest memory aids, such as temporary reminders of the new items, will offset the increased memory load. However, when reorganization and up-dating are required, aids that keep track especially of the once-but-no-longer relevant items are especially helpful. Memory up-dating of the current state of a complex systems is uniquely vulnerable to the effects of information load and possible other stressors.
Adding a secondary task to a primary task can create an information overload situation, but information overload can also occur within the context of a single, primary task. Suppose individuals are required to learn rapidly a large quantity of new facts in some specific domain, which is commonly the case with the introduction of new complex systems into the workplace. The effects of this kind
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of information overload on learning and subsequent performance are not well understood by cognitive psychologists but should generally be detrimental. If the overload is severe, then it will impose a form of cognitive stress (Humara, 2002), and it is important for the operator to develop coping strategies to deal with this stress. Van Overschelde and Healy (2001) recently reported a series of experiments to investigate how the level of knowledge participants have about a domain affects their ability to cope with a large number of new, non-domain relevant facts about persons within their domain of expertise. To create a situation of information overload, Van Overschelde and Healy required subjects to learn 12 new facts about each of 12 persons (i.e., 144 new facts in total). They found that subjects who had a high degree of knowledge in a particular domain (e.g., about baseball or movies) were better able to learn new facts about famous persons from that domain than to learn new facts about persons from a domain of which they had a low degree of knowledge, even though the facts themselves were not relevant to either domain.
In a second experiment, Van Overschelde and Healy created a novel knowledge base, by having subjects learn five facts about each of six previously unknown persons, and one fact about each of six other persons. Two days subsequent to this pre-training experience, participants learned 12 new facts about each of the 12 persons. Participants were significantly better at learning new facts about persons for whom they had learned five facts initially than about persons for whom they had learned only one fact initially.
As noted earlier, these studies suggest that one mechanism for coping with information overload and reducing the stress overload engenders is to provide connections between the new facts to be learned and an existing knowledge base.
The general principle is that the acquisition and retention of new, factual information is facilitated whenever that new information can be linked to an existing knowledge base. The mechanism underlying this strategic-use-ofknowledge principle is based on the provision of a retrieval strategy supported by factual information that already exists in long-term memory. Future experiments might profitably focus on the provision of different retrieval strategies to validate their effectiveness and to document which strategies work best.
Fatigue and Sleep Deprivation
Laboratory studies. When a people work at a continuous, demanding task, such as the operation of a complex electronic system, their performance might be affected by at least two opposing processes. First, performance might improve, becoming more accurate and faster as operators master the skills required of the task. Second, performance might deteriorate as individuals suffer the effects of
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fatigue over long periods of uninterrupted work. The effects of fatigue are likely to be transient, dissipating over periods of rest interpolated between periods of work.
The effects of skill acquisition, however, should be relatively permanent, persisting long after fatigue has worn off. Testing this differential effect of prolonged work has yet to be adequately accomplished and is likely to be the focus of future research in the general domain of stress (caused by fatigue) and cognition.
Healy, Bourne, and colleagues (Buck-Gengler & Healy, 2001; see also
Fendrich, Gesi, Healy, & Bourne, 1995) have recently reported several experiments addressing certain aspects of fatigue in a repetitive data entry task. In one experiment, there were two sessions separated by a one-week delay. In each session, subjects typed strings of 4-digit numbers viewed as numerals displayed on a screen. A short break halfway through the first (training) session allowed subjects some degree of recovery from fatigue. These researchers found that, during training in the first session, accuracy of performance decreased from the first to the second half of the session and across blocks within each session half.
This finding documents the successful induction of fatigue during training.
Nevertheless, these researchers also found that, during training, response time decreased from the first to the second half of the session and across blocks within each session half, suggesting that practice and fatigue combined to lead to a speedaccuracy tradeoff.
The observed speed-accuracy trade-off illustrates two important general caveats concerning the effects of stressors, such as fatigue, on performance. The first is that stress effects may be different for different measures or indices of performance (in this case, speed and accuracy). The second is that the effects of stressors may not always be harmful. This latter conclusion, of course, follows from the Y-D law, which specifies an optimal level of arousal (resulting from stress) for any person and any task. But what is demonstrated in these experiments is slightly different; here one stressor actually facilitates response times and simultaneously inhibits accuracy. The generality of this observation needs to be checked in other tasks and training conditions. For example, in a more cognitively demanding task than data entry, such as mental calculation (e.g., Rickard, Healy, &
Bourne, 1994), fatigue effects might be less severe or possibly non-differential on performance measures.
The observation that fatigue or other stressors might not matter or might even have a beneficial effect on some measures of performance seems inconsistent with common sense and is certainly contrary to corporate wisdom. Every manager knows that if you keep people up for 48 hrs, they will not handle the workload as
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well as they can when they are fresh. To interpret these results accurately, we need to keep in mind that the level of fatigue induced in laboratory studies might simply be too minimal to cause serious performance degradation. It is also important to recognize that most cognitive studies performed in the laboratory have addressed acute fatigue developed over relatively short work periods. Principles uncovered in these conditions are unlikely to apply to more chronic or stronger fatigue states.
Therefore, in the future, experimenters should try to find ways to expand their research on fatigue both to more intense and to chronic conditions. This expansion might be accomplished, for example, by the use of sleep deprivation or imposed deviations from normal circadian rhythms.
The results of Soetens, Hueting, and Wauters (1992) show that the effects of fatigue might vary with task difficulty. Using a numerosity judgement task, these researchers found that, under fatigue, errors were greater for larger displays (7+ dots in the visual field to be judged). No difference between fatigued and nonfatigued subjects were observed at smaller displays. Small numbers can be estimated accurately by an automatic process known as subitizing. Larger numbers require attention and mental work, including counting. Fatigue reduces or eliminates controlled processing required by larger numbers, leading to more errors. Their conclusion was that fatigued subjects tend to avoid or fail at complex decisions. Steyvers and Gaillard (1993) examined the possibility that knowledge of results (KR) and reward might compensate for the negative effects of sleep deprivation in a choice-reaction task. They found that the effect of signal degradation on performance was aggravated by sleep loss and time-on-task, confirming the observation of Soetens, et al. (1992). They also reported that KR improved performance, especially when signals were degraded. Reward counteracted to some extent the effects of time-on-task owing to lack of sleep.
Consistent with the finding of Buck-Gengler and Healy (2001), performance also improved as the result of a brief task interruption after 30 min. of work.
EEG measures are sensitive to abnormal conditions such as fatigue and sleep deprivation. This fact suggests the possibility that neuro-physiological measures, such as the EEG, might be used to differentiate stress states of the organism from normal or other abnormal states. Gevins and Smith (1999) reported that both alcohol intoxication and fatigue reduced the accuracy of performance in a working memory task and that these effects were associated with changes in spectral characteristics of the EEG. Human observers and digital networks trained
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on human data could discriminate fatigue and alcohol states in the EEG from normal alert states with accuracy well over 90%.
Natural tasks. There has been a fair amount of research on fatigue in more natural situations. For example, Matthews and Desmond (2002) induced fatigue in a simulated driving task by requiring subjects to perform a demanding secondary task while driving. Their induction procedure produced subjective feelings of fatigue and stress and of heightened workload. With respect to driving performance, fatigue induction increased errors of heading, steering, and reduced perceptual sensitivity in the secondary task. These researchers also report, however that added motivation partially overcame these adverse effects of stress.
They attributed the primary effect of a secondary task (1) to the division of attentional resources in the dual task case and (2) to a failure to adjust effort to level of task demands.
Schellekens, Sijtsma, Vegter, and Meijman (2000) demonstrated some persistent effects of demanding day-long office work on cognition. These researchers administered a memory search task before, during, immediately after, and 2 hrs. after either an easy day of work or a demanding day of work.
Performance measures on the search task were RT and accuracy. Effort on task was measured physiologically by HR. Accuracy decreased slightly on the immediate test after a difficult day, relative to tests administered before and during the work-day. Also, subjects invested significantly less effort in the memory task after a difficult day relative to an easy day. In a delayed test, a speed/accuracy trade off was observed. After a demanding day, RTs increased and accuracy decreased in the delayed measure, results similar to those reported by BuckGengler and Healy (2001) obtained in a laboratory setting. Apparently, under some circumstances, fatigue has latent effects that only show up after sufficient passage of time. Further, recovery from fatigue requires rest and time away from task.
Many occupations require not only extended work periods, exceeding the normal 8 hrs, but also are physically demanding and provide few if any breaks.
Operators of public transportation equipment are a good example of this kind of work environment. Raggatt and Morrissey (1997) measured stress and arousal in
10 long-distance bus drivers during 12-hr driving shifts and at matched times on non-driving rest days. The objectives of the study were (1) to compare the stress measures collected on the road, which included HR, BP, catecholamines, cortisol, state anxiety, and self-ratings of stress and arousal, with matched rest-day baseline measures, and (2) to investigate the pattern of arousal over the course of shifts. It was expected that certain psycho-physiological changes would take place during
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long-distance driving and these changes would be associated with driving fatigue.
Cardiovascular and catecholamine data were elevated across the entire work-day, compared with rest days. Self-reported stress and state anxiety were elevated only at the pre-shift measure, and these elevations were interpreted to be the result of anticipatory anxiety and additional work demands at the beginning of the shift.
Decelerating activation from the 9th-12th hrs of driving were reflected in slower
HR and lower subjective arousal ratings. Apparently drivers experience a release of tension when they anticipate the end of the shift and therefore deactivation is a signal or precursor to the onset of fatigue. Measures of driving performance remained relatively stable over a 12 hr shift. Experienced drivers seem to have acquired coping strategies that allow them to maintain stable performance levels when work sessions are of known duration and do not exceed 12 hrs. As in the case of long-term isolation, cognitive effects of stress appear to be ameliorated by knowledge that the stressful situation, although long, is time limited
But Raggatt amd Morrissey (1997) also found that performance falls when shift length is uncertain or exceeds the normal 12 hr limit. Performance degrades before changes are evident in physiological measures. This result is consistent with the conclusion of Hancock and Vasmatzidis (1998) that continued work requirements after performance efficiency begins to fail, but before current physiological limits are reached, is inappropriate for both the safety and the productivity of the individual worker, their colleagues, and the systems within which they operate. Behavioral performance assessment should therefore supercede physiological assessment as the primary exposure criterion, although physiological measures still provide important supplementary information.
Even without a work requirement, long periods of sleep deprivation can have serious cognitive consequences. Baranski, Gil, McLellan, Moroz, Buguet, and Radomski (2002), for example, showed that 40 hrs of sleep deprivation severely affected cognitive performance on seven cognitive tasks -- serial reaction time, logical reasoning, visual comparison, mental addition, vigilance, and multitasking -- to essentially the same degree on all tasks.
Samel, Wegmann, Vejvoda, Drescher, Gundel, Manzey, and Wensel (1997) investigated two-person crew extended range operations over 2 consecutive night flights with a short layover. Pre-, in-, and post-flight measurements of sleep, task load, fatigue, and stress using EEG, ECG, motor activity and subjective ratings were collected for 11 rotations (22 flights) from 22 male pilots. Average flight times were 9 hrs with an average daytime layover of 13 hrs 30 mins. Results showed that sleep during layover was shortened by an average of 2 hrs relative to
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normal. Fatigue was more pronounced during the return flight and several pilots scored their fatigue at a critical level. Motor activity, brain wave activity, and HR indicated drowsiness and a low state of vigilance and alertness during both night flights, but these effects were more pronounced during the return flight. A survey of military pilots reveals that they suffer chronically from sleep deprivation
(Caldwell & Gilreath, 2002). Insufficient sleep, combined with rotating schedules and other work demands, no doubt contributes to the perception that fatigue is a widespread problem in the aviation community. These results indicate the importance of continuing to employ fatigue-reduction strategies in training and operational environments.
To what degree can fatigue effects be offset by periods of rest? Neri,
Oyung, Colletti, Mallis, Tam, and Dinges (2002) arranged for 14 2-man crews to participate in a 6 hr, uneventful, nighttime flight in a Boeing 747-400 flight simulator. Crew members in the treatment group received 5 short breaks spaced hourly during cruise; the 14 crew members in the control group received 1 longer break in the middle of cruise. The treatment group reported significantly greater subjective alertness for up to 25 min. post-break, with strongest effects near the time of the circadian trough. There was no evidence of objective vigilance performance improvement at 15-25 min. post-break, with expected performance deterioration occurring due to elevated sleep drive and circadian time. In situations that require sustained attention over a prolonged period of time, e.g., during a long overnight flight, brief and regularly spaced breaks improve alertness and performance. What about stimulating drugs? Can they offset the effects of fatigue, without causing adverse consequences of their own? Caldwell (2001; see also
Caldwell & Gilreath, 2002) reported a quasi-experimental comparison of modafinil
(Provigil (R)) and dextroamphetamine (Dexedrine (R)) on the performance of sleep deprived pilots. Subjects were given either dextroamphetamine or modafinil and then undertook a flight simulation. Results indicate that there were no differences between the 2 stimulants. However, in the majority of cases, it was clear that performance, subjective mood ratings, and physiological indices of alertness were substantially better under both drugs than under placebo. Thus, with the exception that modafinil produced more spontaneous reports of side effects than dextroamphetamine, the overall results indicated equivalent efficacy with the
2 compounds.
There are at least two studies which have examined the interaction of sleep deprivation with other stressor variables. von Restorff, Kleinhanss, Schaad, and
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Gorges (1989) investigated human tolerance limits for sustained performance on several simple psychological tests. Subjects performed continuously for 72 hr, with only 1 hr of sleep permitted after 32, 48 and 60 hr. The present experiment examined whether such sustained performance might be additionally influenced by mild hypoxia together with correspondingly increased carbon dioxide levels (stale air). Performance showed the expected decrease with increasing duration of sleep loss. However, findings show no clear differences in performance between the control and the hypoxia groups. There were, however, more pronounced decreases over time in both group in the more complex memory tasks as compared to simple reaction time and vigilance tasks.
Larsson (1989) looked at the interaction of sleep deprivation and the stress created by a noisy work environment. He measured the performance of Swedish military personnel on an artillery simulator under calm conditions, noisy conditions, and noisy conditions with 27 hrs sleep deprivation. Under all conditions, subjects who appraised the task as a challenge demonstrated positive coping and better performance, relative to those who appraised the situation as a threat. Performance degraded and negative coping increased with increasing sleep deprivation. Noise
Noise or atonal sound is everywhere in the modern world. People normally do well in adapting to these ambient and sometimes disagreeable sounds. But there are circumstances in which noise can be stressful enough to produce some adverse changes in human behavior. Early on, Hockey (1979) reviewed the psychological literature on noise-induced stress, concluding that there were five primary effects. First, stressful noise activates the performer often to a level that exceeds optimal for the task at hand, resulting in an increase in the rate of work but also an increase in errors. Second, stressful noise changes the performer’s policy for allocating attentional capacity, resulting in an apparent reduction in short-term or working memory. Third, attentional selectivity -- that is, limiting the attentional field, bringing relevant stimuli into sharper focus, focusing on the here and now, reducing memory search, relying on automatic as opposed to deliberate functions - is increased. Fourth, there is an increase in response selectivity. Finally, stressful noise reduces the performers confidence in his/her ability to do the task at hand.
These effects were observed primarily in studies using laboratory induced stress and laboratory tasks.
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Later, Kjellberg (1990) reviewed the psychological literature on the effects of noise in the work environment, emphasizing moderate-intensity noise (e.g., computers, printers, and ventilation systems). He found reports of significant distraction, and sleep disturbance in individuals who worked under constant noise conditions. He also found evidence of noise effects on reaction time (RT), vigilance, and verbal comprehension tasks. But, in many respects, the existing research presented a rather inconsistent picture of noise effects in natural work environments. Kjellberg (1990) recommended that, because of the potential seriousness of the nonauditory, cognitive effects of noise, more attention needs to be given to these effects in the occupational setting and in the research laboratory.
Little has changed in the last 10 years to modify that recommendation.
Larsson (1989) reported that performance by Swedish military personnel on an artillery simulator, a task requiring target identification, target tracking, decision making, and perceptual-motor co-ordination, degraded significantly in noisy conditions relative to calm and quiet conditions.
Kjellberg, Landstroem, Tesarz, et al. (1996) followed up a review of the noise literature (Kjellberg, 1990) with an examination of some of the factors that influence subjective responses to noise in 439 persons working in offices, laboratories, or industrial settings. Information about the workers’ subjective assessment of their working environment was collected by questionnaires. An annoyance index and a distraction index were formed on the basis of a factor analysis of questionnaire data. Annoyance was found mainly to be related to sound level, self-rated "necessity" of the noise, hearing status, and gender. Distraction was most strongly related to degree of self-control of the noise and noise predictability. The most critical noise sources for the annoyance response were other machines than those used by oneself, whereas telephone signals and conversations had the largest effect on distraction. Despite the annoyance and distraction effects of workplace noise, no significant influence on quality or quantity of work performance was detected. A moderate level of workplace noise might be stressful, but its potentially degrading effect on performance appears to be counteracted by extra effort in most circumstances.
In a related study, Gomes, Martinho Pimenta, and Castelo Branco (1999) investigated the effects of prolonged workplace exposure to large pressure amplitude (-90 dB SPL) and low frequency (
References: Complex operations can be performed successfully in Space by human beings, but more slowly than doing the same tasks on Earth (Fowler, Comfort & Bock, 2000; Watt, 1997)), Fowler, et al. (2000) and Manzey (2000) propose two hypotheses to account for this performance degradation—(1) the direct effects of microgravity on the central of human performance in Space, as suggested by the results of Watt (1997) among others, cognitive psychology can help solve the problem (2002) describes how 20 years of experience working in the Pentagon convinced him of the need for a greater understanding of human behavior and of human-machine interactions to improve military operations. Wastell and Newman (1996) have argued that a well-designed military system should realize the twin aims of enhancing human the military, which are especially concerned about performance of people in extraordinary conditions (see, eg., Dearnaley & Warr, 1979). clearly a distinct advantage to anyone caught in an emergency. Neufield (1999) has recently offered a promising formalism, based on nonlinear dynamics, that helps us studies of health and performance changes in chronically stressful circumstances. For example, Sauer, Juergen, Hockey, and Wastell (1999) reported a study of three Russian
Final Report
STRESS AND COGNITION: A COGNITIVE
PSYCHOLOGICAL PERSPECTIVE
National Aeronautics and Space Administration
Grant Number NAG2-1561
Lyle E. Bourne, Jr. and Rita A. Yaroush
February 1, 2003
1
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Outline
Stress and Cognition: A Cognitive Psychological Perspective
Introduction
Cognition in Emergency and other Abnormal Situations
Acute and Chronic Stress
Teamwork under Emergencies
The Purpose of this Review
Preliminary Guidelines from Cognitive Psychology
An Example
Research Methods
Measures of Stress Effects
Neuro-physiological Measures of Stress
Self- report Measures
Performance or Behavioral Measures
Conclusions
Definitions of Stress
Theories of Stress and Cognition
Conclusions
Arousal and Performance.
Motivation and Arousal
Stress and Arousal
Stress States: Qualitative Effects of Stress
Conclusions
Appraisal
Conclusions
Attention and Perception
Inhibition and Attention
Perception and Cue Utilization
Vigilance
Conclusions
Stress and Cognition
Memory
General Stress Effects on Memory.
Cortisol and other Neuro-biological Considerations..
Context And State Dependency involving Stress.
Other Considerations
A Memory Constriction Hypothesis
Conclusions
Environmental Conditions that Induce Stress
Time Pressure
Work Load and Overload
Fatigue and Sleep Deprivation
Noise
Ambient Temperature
Miscellaneous Stress Variables: Extreme Environments
Conclusions
Individual Differences Variables
Trait Anxiety and Stress
Other Personality Variables
Health and Coping Styles
Conclusions
Stress Countermeasures
Task Conditions
Stress Management
Conclusions
Other Reviews of the Literature
Summary and Conclusions
References
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Stress and Cognition: A Cognitive Psychological Perspective
Lyle E. Bourne, Jr. and Rita A. Yaroush
University of Colorado
Complex operations can be performed successfully in Space by human beings, but more slowly than doing the same tasks on Earth (Fowler, Comfort & Bock, 2000; Watt,
1997)), Fowler, et al. (2000) and Manzey (2000) propose two hypotheses to account for this performance degradation—(1) the direct effects of microgravity on the central nervous system and the motor system of the body and (2) the non-specific effects of multiple stressors. Evidence available to date is consistent with both hypotheses and further experiments are required to settle this question. The issue has practical implications because the countermeasures needed to ameliorate or prevent performance deficits will differ according to which hypothesis is correct. Understanding and ameliorating performance deficits will surely help ensure safer operations aboard the
International Space Station and during a mission to Mars.
Introduction
To the extent that the effects of multiple stressors are involved in the degradation of human performance in Space, as suggested by the results of Watt (1997) among others, cognitive psychology can help solve the problem. In a retrospective piece, Rapmund
(2002) describes how 20 years of experience working in the Pentagon convinced him of the need for a greater understanding of human behavior and of human-machine interactions to improve military operations. Wastell and Newman (1996) have argued that a well-designed military system should realize the twin aims of enhancing human performance and lowering stress. Success in this endeavor, they demonstrate, depends on the degree of support and controllability the system affords the operator.
Cognitive psychologists study things that people do in their heads and how they subsequently perform based on those mental operations. Cognitive psychology is largely an academic discipline and a basic science, concerned primarily with (a) identifying analytically the fundamental components of mental life, such as attention and its allocation, memory systems, problem solving, decision making and the like, (b) constructing experimental paradigms to isolate and examine these components in the laboratory, and (c) developing theoretical structures that help to make sense of the data collected in these paradigms. But the field is not exclusively academic. General principles have been uncovered over roughly the last forty years of laboratory research on
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cognition and some of those principles show promise of fruitful application to natural situations, especially in education and training.
Cognition in Emergency and other Abnormal Situations
One important issue to which contemporary cognitive research might usefully be addressed is behavior under stress and in emergencies or other abnormal situations.
Interest in this problem is not new, having been expressed throughout the history of psychology as an independent discipline and particularly by governmental agencies and the military, which are especially concerned about performance of people in extraordinary conditions (see, eg., Dearnaley & Warr, 1979).
Emergency situations are almost always dynamic, because early actions by a participant determine the environment in which his or her subsequent decisions must be made. Further, features of the task environment may change independently of the participant’s actions. Emergencies are time-dependent, because decisions must be made at the correct moment in relation to environmental demands. Emergencies tend to be complex, in the sense that most variables are not related to each other in one-to-one manner. Finally, emergencies are stressful, because they can create intense psychological pressures on participants.
Acute and chronic stress
Emergencies typically are not single isolated events. They are more like episodes extending in time. Thus, emergency situations often require not one decision about how to react, but a long series of decisions, and these decisions are, in turn, at least partly dependent on one another. For a task that is changing continuously, the same action can be definitive at one moment and useless at another. People often perform badly in emergencies, sometimes neglecting to respond correctly in even the most obvious ways.
One bad decision can worsen the situation and augment the importance of later decisions.
A poor decision or an inadequate response can compound the stress effects that are a consequence of the emergency itself. Being able to respond rapidly and correctly is clearly a distinct advantage to anyone caught in an emergency. Neufield (1999) has recently offered a promising formalism, based on nonlinear dynamics, that helps us understand the interaction of multiple variables operating over time, as in emergencies and in cases of stress and coping with stress. But there are presently few data available to test the adequacy of Neufield’s theory.
Emergencies often create acute conditions of stress, but these effects subside after the emergency has passed. Other conditions that are non-normal but might not involve
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emergencies can also be stressful. Many of these conditions generate longer term or chronic, in contrast to acute stress. Among these conditions are space flight, confinement, isolation, and other similar protracted exposures to abnormal circumstances.
Anecdotally, human beings have demonstrated an exceptional ability to live, work, and adapt to extreme environments. Sauer, Hockey, and collaborators conducted a series of studies of health and performance changes in chronically stressful circumstances. For example, Sauer, Juergen, Hockey, and Wastell (1999) reported a study of three Russian cosmonauts, tested on a PC-based simulation of a MIR space flight, including isolation and confinement over time. They found some temporary performance degradations as time passed although for the most part, without the occurrence of emergencies, job performance was acceptably high. The same researchers also reported on the effects of wintering-over by a group of French Antarctic expeditionaries. They, like Brubakk
(2000), argued that polar expeditions provide a better, more natural model of life in Space than do confinement or isolation studies. Again, only small decrements in performance on cognitive tasks were observed. Zulley (2000) reviewed the results of experiments performed in a wide variety of long-term isolating environments including Space, focusing on the circadian course of variables such as body core temperature, sleep-wake patterns, mood, and performance. He concluded that subjects in isolation can experience disturbances of sleep, mood and vigilance if their biological rhythms run "out of phase."
On the basis of his review, he recommended that, if at all possible, a strict 24-hr. time schedule should be kept with regard to environmental, as well as behavioral influences to insure adequate and restful sleep and optimal levels of waking performance and psychological well-being. Again, no serious degradation in performance tasks attributable to isolation was reported, however.
The job of a commercial airlines pilot is generally regarded as one of the most stressful. It would, therefore, not be surprising to discover that pilots suffer more health problems than non-pilots. Nicholas, et al. (2001) investigated self-reported disease outcomes among a large group of active and retired commercial airline pilots in the
United States and Canada. Increased disease rates among pilots were suggested for melanoma, motor neuron disease, and cataracts. However, rates for other diseases were in general lower than those for the U. S. population. As with others who are exposed to stress over extended periods of time, commercial airline pilots appear to adapt well and to evidence few serious behavioral problems as a consequence of job-related stress.
The counterintuitive message from this research seems to be that if participants are well prepared for the required tasks and understand that their confinement or isolation, while protracted, is time-limited, performance holds up well. Adaptation to chronic stress might be quite good, if the stressful situation is not prolonged indefinitely. If adverse conditions do persist, however, and there is no clear end-point to the stressful
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circumstances, there are at least some indications of possible significant cognitive effects, especially in children (Haines, Stansfeld, Job, Berglund, & Head, 2001), What unique effects emergencies, occurring during chronically stressful conditions, might have are not clear from these studies. However, it is also the case that prolonged work stress in relatively mundane work settings can have significant effects on a person’s health, especially if the stress creates chronic supra-optimal levels of arousal accompanied by a state of strain in the worker. Straining has been shown to put the performer at some risk regarding health and/or safety (e.g., Andries, Kompier, & Smulders, 1996). High correlations have been found between work stressors and psychosomatic complaints, general health, and felt fatigue and boredom at work (Houtman, Bongers, Smulders, &
Kompier, 1994).
Teamwork under Emergencies
Many emergency situations require teamwork and co-ordination among two or more players. Cockpit emergencies, for example, usually do not happen to a single individual but rather to a crew. The stress associated with the emergency is generated within each crew member, but its most important influence might be on the performance of the crew as a whole. Decisions and responses might be made by individuals but their effects ramify throughout the team. Thus it is imperative to try to understand not only the individual under stress but also how the team functions cognitively in these circumstances. Unfortunately, the literature on this issue is quite limited and largely inconclusive. The Purpose of this Review
Research in cognitive psychology has made a contribution to a understanding of acute and chronic stress effects on performance by identifying some of the factors that contribute to operator error under emergency or other abnormal circumstances and by suggesting how operators might be trained to respond more effectively in these circumstances. The major purpose of this paper is to review the literature of cognitive psychology as it relates to these questions and issues. Because older reviews are available (e.g., Hamilton, & Warburton (1979; Hockey, 1983), we limited our search of the literature to roughly the last 15 years (1988-2002). To anticipate our findings, research published in this time period, as well as the earlier literature, is limited in significant ways. There are many studies to document the effects of stress on cognition, performance, and health, and most indicate stress effects to be adverse. Typically, however, these studies compare only two conditions, stress and no stress. Outside of the clinical literature, there are very few studies that examine stress over a wide range of values. This itself is surprising in view of the fact that most theoretical accounts of stress
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effects in psychology invoke some variation of the inverted U-hypothesis, that is, that there is some optimal level of stress (or arousal) for performance in any task. To verify such a hypothesis, at least three levels of stress must be included in the experiment. The literature is limited in still other ways. Although there are many experiments to document that stress does influence performance, there are very few that assess ways to prepare for or to countervail the effects of stress. That is, we know very little about steps that might be taken to inoculate the performer against stress. There is some literature on training to manage stress when it occurs, but only a few of these studies touch on the benefits of stress management for cognition or performance. Thus, in anticipation of the review to come, its outcome, in the form of a clear and well-documented depiction of the stress/cognition relationship and of recommendations for procedures or guidelines that might be followed to minimize or eliminate adverse stress effects, will be disappointingly meager. As an aside, we expected to find the most significant research on stress and cognition published in the major cognitive journals, e.g., Cognitive Psychology, Memory
& Cognition, the Journal of Experimental Psychology: Learning, Memory, and
Cognition, and similar others. In fact, however, there has been relatively little published on stress in these Journals in the last 10-15 years. Rather, the most important publications that we found appear in peripheral journals, e.g., Aviation, Space, &
Environmental Medicine, Ergonomics, Work & Stress, and the like. There are also many unpublished technical reports available in various data bases. Our review uses few of these technical reports for a number of reasons, most important among them being their lack of peer review and the fact that the best of them often appear later in revised form in a peer-reviewed journal.
Preliminary Guidelines from Cognitive Psychology
An emergency, especially a life-threatening emergency, is a unique challenge to operators of complex systems, such as aircraft. On the one hand, pilots and crewmembers are expected to maintain a high degree of proficiency in the relevant emergency procedures, such that their performance is virtually automatic. Yet, on the other hand an air crew rarely has an opportunity to practice these procedures in natural circumstances.
In aviation, normal flight procedures that are carried out on a daily basis are completed with the benefit of a physical checklist. Emergency procedures, in contrast, are expected to be performed rapidly, accurately, and without external guidance. In addition, the procedures required might not be known if the conditions of emergency are unique.
Studies of memory, conducted within the context of the cognitive psychological laboratory, have a good deal to say about this difficult situation. For one thing, it is not feasible to expect that even a highly experienced operator can execute flawlessly a
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complicated sequence of actions, which have not been recently refreshed, in response to an unexpected and threatening event (Bahrick, Bahrick, Bahrick,& Bahrick, 1993; Healy
& Bourne, 1995). We will attempt to review and organize this experimental memory literature in such a way that the general principles can be identified and translated into guidelines for cockpit procedures. To the extent that we are successful, the result should have important implications for procedures and checklist design and for air-crew training.
Cognitive psychology has produced some promising leads on the effects of stress on human performance. Consider the most general question, what is the nature of responses under stress? The answer is, there is a vast amount of variability in performance. This variability depends, among other things, on who the operator is (a matter of individual differences) and on the situation in which responding takes place
(especially, the type of stress, e.g., time pressure, external threat, etc., engendered).
There is evidence for a continuum of performance, ranging from: (a) no effect (the person handles the emergency situation as he or she would in the absence of stress) to (b) facilitation (a small amount of stress actually improves performance), to (c) varying degrees of degradation (the person makes errors or inadequately slow responses) to (d) choking (characterized by performance failure due to “overthinking” the problem and attending to aspects of the situation that are irrelevant to the task at hand) to (e) outright panic (resulting in primitive ineffective responses, as if no training had ever been given, or complete paralysis). It is obvious that, quantitatively, the intensity of stress elicited by an environment event should move people, in general, from the no effect through various intermediate stages to the panic end of the continuum. It goes without saying that, to determine this effect, objective measures of stress intensity are required. Moreover, people differ in how they respond to the same environmental event. We expect that, by disposition, some people handle stress better than others, and we will present in later sections some organized documentation to that effect. In addition to dispositional sources, individual differences created by training also affect where a person falls on the performance continuum. Degree of original learning or overlearning on the task at hand probably can mitigate some effects of stress, especially at lower stress levels. It seems obvious that skilled procedures that can be engaged on demand and executed flawlessly under normal circumstances stand the best chance of succeeding in an emergency or other abnormal situations. The literature to back this conjecture up will be reviewed.
Assuming that stress generally will, at some point, degrade performance, even well-trained performance, where in the cognitive system are these effects most likely to be found? Perception, attention, memory, decision making, problem solving and response execution, all stages that have been identified and studied by cognitive psychologists, are candidates for degradation. There is a relevant basic science literature on these cognitive processes, both empirical and theoretical. But the relevance of this
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literature to the natural emergency situation is limited by two factors. First of all, cognitive psychologists, in addition to identifying the underlying processes of cognition, have developed laboratory tasks in which to study them individually, more or less uncontaminated by other processes. Thus, there are “attention” tasks or “memory” tasks in which attention or memory is revealed while other processes are eliminated or controlled. These tasks have become standard and are used widely over different laboratories. This has the advantage of providing a check on the replicability of data collected in different locations replicable. But, at the same time, it entails the disadvantage of creating relatively simple tasks that bear little face resemblance to things people do in the real world. Secondly, it is difficult to create real emergencies in the laboratory. Stress manipulations used by cognitive psychologists are mild and marginal, relative to natural emergencies. Both limitations make generalizations from the laboratory to behavior in natural emergencies risky and questionable.
To date, cognitive psychology has shed little light on performance in situations that require the concurrent management of multiple skills. Piloting an airship is one such situation that is characterized by many relevant variables, differing lags in system components, and several independent, simultaneous tasks. O’Hare (1997) and Wickens
(2002) have written extensively on this matter. At the top level, successful performance in piloting requires simultaneous awareness for one’s position in space, of the state of the many variables comprising the operations system, and of the various task requirements.
These competing demands often exceed the operator’s finite attentional resources. The
PC-based WOMBAT-super(TM ) Situational Awareness and Stress Tolerance Test has been designed to measure individual aptitude to cope with such demands (O’Hare, 1997).
Because of the high mental workload imposed by flight, a pilot might fail to maintain full awareness of the environment and, at various times, neglect certain critically important component tasks. Performance on the WOMBAT test reliably distinguishes between elite pilots and similarly experienced but less skilled pilots (O’Hare, 1997). Loss of awareness has been identified as a major contributor to human error in aviation accidents (Li, Baker,
Lamb, Grabowski, & Rebock, 2002). Moreover, there is no doubt that loss of awareness can be stressful. Indeed, anticipation of possible loss of awareness might be stressful, leading to some cases of performance degradation or errors as arousal increases.
Wickens (2002) has described the cognitive processes involved in piloting an aircraft and the changes in them that come with cockpit challenges. He notes that basic experimental cognitive psychology has produced a reasonable understanding of these processes in isolation or in simple (dual task) combinations. But presently we lack a full understanding or successful modeling of the complex interactions among these processes that occurs in many natural situations.
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That having been said, it is still the case that basic cognitive research has identified some important general principles regarding stress and performance. These principles are known to apply when individual cognitive processes are isolated and studied analytically.
To the extent that these processes are involved in more complicated naturalistic emergency situations, the principles so identified have something to say about behavior in emergencies. In other words, they should help us to understand and account for behavior of persons in real situations. Beyond that, we will be able to abstract out of this basic literature some useful recommendations about procedures and guidelines for effective performance in real emergency situations.
An Example
An example might be useful at this point. Cognitive research currently is concerned with a variety of forms of memory. One important distinction applies to the temporal focus of information retrieved from memory. This distinction is based on a continuum from the remote past – retrospective long term memory – to the present or near present – short term memory and immediate or working memory – to the future – prospective memory. Long term memory is theoretically a repository for facts and skills acquired in the past. Short term and immediate memory holds facts and skills that are currently at the focus of attention. Prospective memory contains reminders of actions to be executed at some future time and place. Laboratory tasks have been invented to study each of these forms of memory and the factors that influence them. The fundamental processes and the important variables influencing memory are not necessarily the same in all cases. Long term memories are characterized, for example, by loss of detail and partial retrieval whereas immediate memories and especially prospective memories are more likely to be all-or-none, i.e., complete or absent. Whether the memories in question relate to facts (episodic memories) or skills (procedural memories) is also an issue.
Specific fact memory tends to blur into generic representations over the long term, whereas skill simply degrades to lower levels of achievement.
Stress effects have been studied in the context of various forms of memory, although the data available are surprisingly skimpy. The evidence seems to suggest that stress in general (including stress arising in emergency situations) causes the operator to focus on the here-and-now, with consequent degradation in retrospective and prospective memory. The results are consistent with a memory constriction hypothesis to the effect that the time span from which knowledge can easily be retrieved and used in a given context shrinks as stress level increases. Neglect of facts or procedures in long term memory and failure to execute required behaviors at appointed future times might be major reasons for performance errors or failures in emergencies. At the present time,
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empirical evidence to support this hypothesis is weak. The hypothesis could, however, serve as a framework for future research efforts.
Research Methods
In the review that follows, our focus will be on the basic science literature. But we will not exclude naturalistic observations and case studies. To the extent possible we will examine the naturalistic decision making and problem solving literature in an attempt to find parallels with what has been learned in the laboratory. In fact, as noted above, the basic literature in cognitive psychology is quite disappointing. Basic researchers seem to have lost interest in stress during the last 15-20 years, judging by the number of publications in the prime journals. Consequently, we have broadened the search, and will reference articles in sports psychology, health, organizational and industrial psychology, human factors, aviation psychology, psychophysiology, ergonomics and other areas. We have found a considerable literature on situation-specific stress, as in stress in the workplace, in the office, among high level managers, in military operations, in airplanes, among air traffic controllers, in autos while driving, in buses, among police and firefighters (see, e.g., Raggatt & Morrissey, 1977; Westman, 1996; Westman & Eden,
1996; Zeier, 1994), but again the general implications are limited.. The research in these peripheral areas tends to be limited and a little simplistic, involving two-group comparisons (stress/no stress), biological correlates of stress, case or correlational studies, intervention studies, and while the literature is considerable, it does not tell us much about basic or practical principles.
Measures of Stress Effects
Neuro-physiological Measures of Stress
Situations capable of initiating physiological stress responses are varied and complex. In the animal literature, stressors have been classified into two categories
(Herman & Cullinan, 1997). One category, termed “systemic” stressors, includes many situations that produce direct physiological threats to organisms. Instances of such situations include microbial infections, temperature extremes, dehydration, injuries, and malnourishment. The second category, termed “neurogenic” or “processive” stressors, includes situations that do not immediately threaten an organism’s physiological homeostasis but are perceived as a potential threat. In human beings, instances of processive stressors include psychological and psychosocial situations, requiring significant cognitive processing for their interpretation. In the lives of human beings, the most common challenging situations encountered are in the processive category.
Traumatic-life events such as bereavement or anticipated or actual loss of home are
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familiar examples, but less traumatic events, such as performance anxiety associated with public speaking and examinations, as well as psychosocial pressures from interpersonal relationships and work place settings, are also effective activators of physiological stress responses. Most challenging laboratory situations fall into the processive class of stressors. Such laboratory settings range from cognitive situations demanding high levels of performance on mental arithmetic or the Stroop color-word interference test, to psychosocial situations involving public speaking, interviews, and the presentation of violent videotapes. Biondi and Picardi (1999) in a recent review of the human literature regarding the effects of real-life and laboratory stressors on neurohumoral functions, emphasized the importance of situational appraisal and emotional reactivity as triggers of several stress responses, as originally suggested by others (Lazarus, 1966; Mason, 1975).
The most emotionally “loaded” procedures are thus the ones associated with the strongest physiological stress responses. This association supports the need to examine self-report measures of stress and their correlation with physiological stress responses in future studies. There are several physiological responses that are reliably correlated with the experience of stress and with stressful physical stimuli. This repertoire of responses plays an important role in preparing individuals to cope with putative internal or external stimuli that might threaten their well being or survival. Threats to homeostasis are met by acute physiological responses that are quick and engage two main biological systems.
The first is the sympathetic division of the autonomic nervous system, which controls neural and hormonal processes. Acute psychological stressors generally activate the sympathetic adrenomedullary system. The release of the adrenomedullary catecholamine hormone, adrenaline, is crucial in the preparation of an individual’s “fight or flight” reaction, as first suggested by Walter B. Cannon in the early part of the 20th century.
Additional sympathetic neural activation via noradrenaline release is responsible for a variety of peripheral responses associated with stressful situations, including, but not limited to, increases in heart rate (HR), blood pressure (BP), respiratory rate, perspiration, and inhibition of digestive and sexual functions (Cacioppo, 1994).
The second principal stress-responsive system is the brain-pituitary-adrenocortical axis, which regulates the release of glucocorticoid (GC) hormones into general circulation (Akil, Campeau, Cullinan, Lechan, Toni, Watson, & Moore 1999). Two of the most salient hormonal responses to stress are increases in norepinephrine and cortisol,
GCs manufactured and released by the adrenal cortex. But stress is associated with a number of other neurohumoral responses. For instance, stress increases the release of growth hormone and prolactin and inhibits the release of the thyroid and sex steroid hormones. Many of these hormonal modulations have been linked to the release of cortisol (Nemeroff, 1992). The orchestration of these responses allows the inhibition of
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“vegetative” functions while activating energy metabolism, body defenses, blood flow to the skeletal muscles, and a sharpening of the senses. Farrace, Biselli, Urbani and Ferlini
(1996) have demonstrated the usefulness of these processes in the evaluation of stress responses during flight.
Stress also affects the human immune system. Although chronic stress typically produces suppression of a wide range of immune system parameters, acute stress has been found to stimulate certain aspects of immune functioning (McEwen, 2000).
Specifically, acute stress can trigger aspects of an immune system acute phase response, even in the absence of an infectious agent (Deak, Meriwether, Fleshner, Spencer,
Abouhamze, Moldawer, Grahn, Watkins, & Maier, 1997). This acute phase activation results in a rapid increase in blood levels of certain acute phase proteins, as well as production and secretion into the blood of the immune system related hormone, interleukin-6 (Zhou, Kusnecov, Shurin, DePaoli, & Rabin, 1993). Thus, acute phase activation is potentially another physiological marker of stress that might be useful in human studies. Recent animal studies have provided evidence for stress-induced stimulation of the acute phase response to be at least partially responsible for stressinduced impairments in memory consolidation (Cahill & McGaugh, 1996; Pugh, Nguyen,
Gonyea, Fleshner, Watkins, Maier, & Rudy, 1999). These studies support accumulating evidence for brain activity to be dynamically regulated by immune system factors (Maier,
Watkins, & Fleshner, 1994).
Electrical activity in the brain, as reflected in EEG patterns, are sensitive to certain abnormal human conditions such as alcohol intoxication and fatigue. Gevins and Smith
(1999) reported that both intoxication and fatigue reduced the accuracy of performance in a working memory task and that these effects were associated with changes in spectral characteristics of the EEG. These authors have shown that both human observers, operating intuitively, and computing networks trained on human data can discriminate
EEG patterns associated with fatigue and alcohol states from normal alert states with accuracy well over 90%.
Measures of physiological responses can serve at least three distinct purposes. First, they can help independently to determine the challenging or stressful character of experimental circumstances. They can be used to assess the degree to which the manipulations produce stress independent of the subjective exit interviews and self-report indices. These physiological measures may offer a rigorous between-experiment assessment of the stressful character of the different conditions employed in the laboratory. A second feature of these measures is that they permit an assessment of correlations between physiological and cognitive variables. For example, do the changes produced by stress in cognitive performance relate significantly to concomitant changes
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in particular physiological responses? Third, these measures will allow the investigation of possible mediating relationships between physiological states and cognitive functioning. For example, a given physiological state may not just mark stress but may mediate the effects of stress on performance. Intrinsic circadian variations of stressreactive hormonal levels could be tested to reveal possible mediating effects of such physiological states upon performance, although this research is yet to be conducted.
To measure physiological reactions to stress, the following procedures have been most frequently used and seem most useful. First, with respect to the action of the sympathetic nervous system, researchers have measured a variety of peripheral response measures, including, but not limited to, increases in HR, BP, respiratory rate, perspiration, and inhibition of digestive and sexual functions. These indices are probably most familiar as components of the lie detection procedure. Although they can be controlled cognitively, subjects typically have no reason to attend to these measures while engaged in a focal task. Under these circumstances, peripheral measures have proven to be highly and reliably correlated with other indices of stress level. There is a good deal of research to document the existence of distinct patterns of autonomic nervous system reactions to stressful events (e.g., Lovallo, Pincomb, Brackett, & Wilson, 1990;
Saab & Schneiderman, 1993). People who appraise potentially stressful events as challenges show a reaction consisting of high cardiovascular activity coupled with low vascular resistance. Individuals who appraise the same events as threats show low to moderate cardiac activity and high vascular resistance. Veltman and Gaillard (1996,
1998) investigated the sensitivity of some of the same physiological measures to mental workload in a flight simulator. Several respiratory parameters, HR variability, BP variability, and the gain between systolic BP and heart period all showed differences between rest and flight. Only heart period was sensitive to difficulty levels in the flight task. Among the respiratory parameters, the duration of a respiratory cycle was the most sensitive to changes in workload. Finally, the time between two successive eye-blinks increased and the blink duration decreased as more visual information had to be processed. Second, to tap the brain-pituitary-adrenocortical axis, researchers have measured GC cortisol in the saliva of human subjects. This is a noninvasive measure and can be repeatedly sampled in most experiments (Kirschbaum &
Hellhammer, 1994). Salivary cortisol is closely correlated with free plasma cortisol levels (Vining & McGinley, 1987), and is useful in detecting several forms of acute stress in the laboratory or in the field ( Aardal-Eriksson, Karlberg, &
Holm, 1998; Bassett, Marshall, & Spillane, 1987; McCleery, Bhagwager, Smith,
Goodwin, & Cowen, 2000), including challenging military training (Morgan et al.,
2000). Level of testosterone, which has been shown to be significantly reduced by
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some stress procedures (Elman & Breier, 1997; Hellhammer, Hubert, &
Schurmeyer, 1985; Schulz et al., 1996), can also be measured in saliva of male subjects. Similar determination using estradiol in adult women is usually not warranted because of low correlations between plasma and salivary levels with existing assays and collection methods ( Shirtcliff, Granger, Schwartz, Curran,
Booth, & Overman,2000)). The immune system cytokine product interleukin-6 (Il6), which is elevated in response to a variety of stressors, is another marker of stress measurable in saliva. Salivary Il-6 determination has been reported to correlate highly with the release of cortisol in at least one study ( Perez Navero,
Jaraba Caballero, Ibarra de la Rosa, Jaraba Caballero, Guillen del Castillo,
Montilla Lopez,Tunez Finana, & Romanos Lezcano,1999).
An important issue concerning the various hormonal responses to stress is the fact that cortisol shows a significant circadian rhythm in human beings (Czeisler &
Klerman, 1999). Thus, circulating cortisol levels normally rise and peak during early morning in anticipation of waking and the demands that the waking state produces on energy consumption and metabolism. Circulating cortisol levels thereafter drop throughout the day and are at their lowest in the evening, anticipating the reduced energy expenditure during the sleep period. Any activation of the adrenocortical stress axis is therefore superimposed on this daily rhythm, and the assessment of morning stress can easily be clouded by the already high morning circulating levels.
Despite the difficulties and the complexity of taking physiological measures, they are recommended for any research program that aims to provide a complete picture of the role of stress in human cognitive performance. It should be noted that the strength of a stressor can only be determined by measuring the subjective and physiological response of the individual, because individuals may vary widely in their reactivity to stressful circumstances. Where possible, it is important to determine the extent to which subjective reports of stress correlate with physiological measures. Likewise, it is important to see whether subjective or physiological measures of stress responses are reliable predictors of performance on whatever task is being studied.
Self-report Measures
Stress affects how we perform (behavioral), how we feel (self-report), and many of our bodily functions (neuro-physiological). All three then should be able to serve in some capacity as measures of stress, independent of environmental or physical conditions that are said to be stressful. Systematic and exacting
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experimental studies of stress and its effects on cognition require valid and reliable measures that can be taken both in the laboratory and in the real world. The best work available on the evaluation of subjective states of stress has been reported by
Matthews and his collaborators (e.g., Matthews, in press; Matthews, Joyner,
Gilliland, Campbell, Falconer, & Huggins, 1997).
Matthews et al. (1997) noted that research on the subjective state of stress, until recently, has been limited in scope, focusing primarily on state anxiety and mood. These authors developed a broader index known as the Dundee Stress State
Questionnaire (DSSQ) which provides the first comprehensive multi-dimensional assessment instrument for transitory states associated with stress, arousal, and fatigue. Construction of the DSSQ began with a factor analyses of various paper and pencil measures of stress, available in the literature or developed by the authors. These scales represented three primary categories which the authors refer to as mood measures (focusing on arousal, tension, and hedonic tone), motivation measures (especially intrinsic motivation or interest in the task at hand), and cognition measures (including awareness, interference, self-focus, concentration, and confidence). By factor analysis, these scales generated three secondary dimensions of subjective stress reaction. The first is labeled Task Engagement by the authors, and is described in terms of how much energy, and concentration a person invests in a task. The second is labeled Distress, that is, how much tension, the hedonic tone, and the confidence a person exhibits in task success. Finally,
Worry, or the degree of self-focus and self-esteem expressed and the amount of cognitive interference experienced from intrusive memories and other sources (see,
e.g., Baum, Cohen, & Hall, 1993). Refined scales were then developed to give maximally discriminant measures of Engagement, Distress, and Worry.
Matthews et al (1997) demonstrated empirically that these state dimensions are independent of other state or trait measures available in the personality literature, such as neuroticism. They further showed that these measures are sensitive to external stress manipulations, especially in challenging and demanding tasks. Task engagement scores are high when task demands are intense and the task itself provokes strong intrinsic motivation. Distress is most closely related to capacity overload and time pressure. Demanding tasks are typically distressing, especially when they are appraised as threatening. Finally, worry tends to be associated with self-evaluation as when the nature of the task provokes assessment of personal qualities and goals. But, boring or monotonous tasks or tasks that lead to a loss of concentration can also provoke worry. Matthews et al. (1997) have developed a processing efficiency theory that predicts slower memory scanning and retrieval in subjects with high chronic stress or high anxiety, because some of
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the working memory capacity of these subjects is occupied by worries, more than low anxious or nonstressed subjects. Ashcraft (2002) has attempted to test this theory directly, and reports inconsistent results. But the hypothesis is plausible and deserves further empirical investigation.
Basically, Matthews, et al. (1997) have shown that much of the variation in the subjective stress state can be characterized by the three themes, labeled commitment to the task, cognitive overload, and self-evaluation, all of which are accessible by self-report. Matthews (1996) suggested that these themes represent the t hree p rincipal a daptive c hallenges p osed b y s tressful p erformance environments and that basic state reactions reflect choices of adaptive strategy within a variety of different situations. The evidence supporting the validity and reliability of the DSSQ is extensive and impressive. As noted above, it represents the most comprehensive measure of subjective stress presently available. Its utility in research might be limited, however, by the length of the questionnaire and the time required to administer it, which is estimated to be approximately 10-15 mins.
If stress measures can be taken before or after the fact, then the questionnaire is probably t he b est i nstrument a vailable. I f s tress m easures a re r equired concurrently with stress conditions and/or on a moment-by-moment basis, other less reliable indices will probably be necessary. It might be possible to develop a short-form instrument, based in the DSSQ, that could be used for concurrent measurement, but such a test has yet to be published.
Task induced changes in stress are described within Matthews’ system as patterned shifts in task engagement, distress, and worry. Patterns are sensitive to task and environmental demands. Matthews et al. illustrated this effect with studies of automobile driving. Operators’ appraisal of task demands (workload) and choice of coping strategy mediate these stress effects. Thus, for Matthews, stress is an adaptive transaction between operator and task. Matthews et al. speculate that the consequences of task automation (e.g., cockpit automation) will vary widely depending on appraisal of the reliability and ease of control of the system, type and number of residual tasks left to the operator, and interpersonal factors such as personality and coping style. Thus there is likely to be no simple remedy for stress-related problems associated with automation, such as boredom or complacency. Fine-grained assessment of the operator’s feeling state and cognitions is required to determine vulnerability to performance degradation under stress. Stress and Cognition
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Evidence from Matthews et al. (1997), based on self-report measures, supports the following guidelines for mitigating the effects of stress in automated and semi-automated systems, such as driving an automobile or flying an airplane.
1. Delineate and focus on those actions and problems that are subject to operator control.
2. Recognize that there are qualitatively different stress-reactions that require different interventions. Stress attributable to fatigue and task disengagement are different from those attributable to distress or worry.
3. Design the system with stress factors in mind. For example, avoid overload on operator controlled tasks.
4. Design for variablity of work load requirements.
A number of specific self-report techniques have been developed to measure stress in the work place, and some of these have possibilities as general stress measures. Quick (1998) has provided an excellent summary of these measuring devises, which include the following.
(1)
The Occupational Stress Indicator and its successor, the Pressure
Management Indicator (PMI, Williams & Cooper, 1998). The PMI presents a range of 22 sub-scales that tap into a number of aspects of the organizational stress process, from demands through moderators and modifiers to strain and distress responses. The PMI also provides information on organizational constructs such as organizational climate and individual constructs such as personal responsibility.
(2)
The Job Content Questionnaire (JCQ, Theorell & Karasek, 1996;
Karasek, Brisson, Kawakami, Houtman, Bongers, & Amick,.1998).), which is a perceptual measure of social and psychological characteristics of jobs and the content of work.
These questionnaires are reliable and valid self-report measures, but are less comprehensive, and therefore less valuable as research tools than the battery developed by Matthews et al. (1997).
How do self-report measures of stress stack up against neuro-physiological indices? Leaving aside for the moment the time it takes to recover these measures, the answer is, quite well. In fact, under many circumstances, self-report measures are to be preferred because of their greater face validity and reliability. There are several studies in the recent literature that speak to this issue. For example, Zeier
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(1994) reported a study that used both self-report and neuro-physiological measures of stress in air traffic controllers. He found that periods of high and low traffic differed in both self-reports and in levels of salivary cortisol. Further he found a high correlation between self-reports and cortisol levels. He concluded that, while these measures differ in substantive ways, the information they provide is supplementary and neither is to be preferred over the other. Both measures might be valid reflections of the same underlying processes.
Shostak and Peterson (1990) found that self-report measures of anxiety level were more sensitive and more reliable as predictors of simple laboratory performance than were two physiological measures, HR and BP. These researchers concluded that self-report measures were further to be preferred in this context because they were easier to take. Kozena, Frantik, and Horvath (1998) reported a similar outcome using middle-aged train drivers. Questionnaire data on health state and family health history, lifestyle, job stress, social and family support, personality characteristics, and health risk behaviors were more predictive of performance in reaction to laboratory stress than were measures of cardiovascular activity, including HR and BP.
Performance or Behavioral Measures
But the issue of which type of measure, self-report or neuro-physiological, is the better or more appropriate measure of stress effects is far from settled. Hancock and Vasmatzidis (1998) contend that, rather than either self-report or physiological measures, task performance level should be the primary criterion for determining the effects of exposure to stress. They argue that change in behavioral performance efficiency is the most sensitive reflection of human response to stress, and that error-free performance is the principal criterion of work efficiency, especially in high-technology systems. Therefore, continuing exposure to stress after work performance efficiency begins to fail, but before current physiological limits are reached, is inappropriate for both the safety and the productivity of the individual worker, their colleagues, and the systems within which they operate. Behavioral performance assessment should therefore supercede physiological assessment or self-report as the primary exposure criterion, although these other measures still provide important supplementary information.
There are, of course, others who disagree with this analysis, contending that how a person thinks and communicates about stress and/or how the body automatically reacts to stress are fundamental components of the stress syndrome that are not contained within measures of performance. Still, there have been
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several significant efforts, following the logic of Hancock and Vasmatzidis, which have been aimed at identifying and developing reliable performance measures to assess individual differences in reactivity to stress. Ackerman and Kanfer (1994) developed a battery of cognitive ability tests for predicting performance under stress. As a test bed, they used a dynamic Target/Threat Identification Task performed under time-pressure. Their final battery consisted of a mixture of cognitive and perceptual speed ability and stress-reactivity measures. They showed that these measures accounted for the major amount of individual differences in performance on a variety of complex tasks. Two tests, called The
Dial Reading and Directional Headings Tests, were found to be particularly promising predictors of performance in stressful information processing activities.
The authors concluded that such measures have definite advantages over selfreports in predicting individual differences in reaction to stress.
A somewhat different set of measures was used by Thomas, Schrot, et al.
(1995). Cognitive processes of primary interest to these authors were memory, speed of response, vigilance, mental calculation, reasoning, and learning. The measures of performance they examined were matching-to-sample, complex reaction time, visual vigilance, serial addition-subtraction, logical reasoning, and repeated acquisition of S-R associations. These measures were implemented in a standardized manner on portable battery-operated computers for use in both laboratory and field settings. Their report provides detailed documentation, supporting the reliability and the sensitivity of these measures to stress effects in a complex operations environment.
Conclusions1
Several physiological responses are reliably correlated with the experience of stress and with stressful physical stimuli. One arises in the autonomic sympathetic nervous system, which controls both neural and hormonal processes The second principal stress-response system is the brain-pituitary-adrenocortical axis, which regulates the release of GC hormones in the general circulation. Two of the most salient hormonal responses to stress are increases in norepinephrine and cortisol, GCs manufactured and released by the adrenal cortex. Third is the immune system, which is also sensitive to stress. Although chronic stress typically produces suppression of a wide range of immune system parameters, acute stress has been found to stimulate certain aspects of immune system function.
1
Conclusions are written in a smaller font than the text. They can be read after the section to which they relate or collectively, in a section entitled Summary and Conclusions, at the end of the report.
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Measures of physiological responses can serve at least three distinct purposes in research.
First, they can help independently to determine the challenging or stressful character of experimental circumstances. Second, they permit an assessment of correlations between physiological and cognitive variables. Third, these measures allow the investigation of possible mediating relationships between physiological states and cognitive functioning. To measure physiological reactions to stress, the following procedures seem most useful. First, with respect to the action of the sympathetic nervous system, researchers have examined a variety of peripheral response measures, including, but not limited to, increases in HR, BP, respiratory rate, perspiration, and inhibition of digestive and sexual functions. Second, with respect to the brainpituitary-adrenocortical axis, researchers have measured GC cortisol in the saliva of human subjects. The immune system cytokine product interleukin-6 (Il-6), which is elevated in response to a variety of stressors, is another marker of stress measureable in saliva.
The most successful self-report measures of stress focus on three processes: commitment to the task, feelings of cognitive overload, and self-assessment of success. Context-induced changes in stress result in patterned shifts in task engagement, distress, and worry on the part of the subject. Patterns are sensitive to task and environmental demands. Comparisons of the value of self-report to neuro-physiological measures of stress have been inconclusive. Most researchers find a high correlation between these two types of measures, leading to the conclusion that, while these measures differ in substantive ways, the information they provide is supplementary and neither is to be preferred over the other. Other researchers have argued that changes in behavioral performance efficiency are the most sensitive reflection of human response to stress, and that behavioral measures are sometimes preferable to both self-report and neuro-physiological measures.
Definitions of Stress
Stress is a descriptive term used in both the behavioral and biological sciences to cover conditions of a physical, biological, or psychological nature, that typically cannot be controlled by organisms, and that strain organisms often beyond their powers to adapt (e.g., Gaillard & Wientject, 1994). But there is no single universally agreed to definition of stress and consequently no single measure that will tell us when a person is stressed or operating under stressful conditions
(Hancock & Desmond, 2001). Some conditions have generally been accepted at stressful. For human beings, these include but are not limited to extreme temperatures, loud or noxious noises, infectious diseases, sleep deprivation, extreme heavy or prolonged work loads, time pressures, social pressures, and intense negatively-toned emotions. Stressors are environmental, biological, and/or cognitive events that, among other things, challenge or threaten the well-being of an organism, increase its arousal or activation level, and deplete its resources (see,
e.g., Hobfoll, 1991). They can be extraneous (non-work stress) or indigenous
(stress created by the task) and they can arise from endogenous or exogenous sources. The resulting stress states can be acute and time limited, as in responses
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to a single transitory event, or they can be chronic, as when the condition of stress persists in time. Normally, human beings respond to stressors either through extraordinary mental or physical effort or by exhibiting degraded performance.
Extreme effort over time in response to chronic stress can result in either mental or physical exhaustion or injury (see, e.g., Kolich & Wong-Reiger, 1999).
With respect to human performance, stress-related phenomena are often classified as emotional, cognitive, and physical (Van Gemmert & Van Galen,
1997). There are numerous examples of the effects of stressors in all three categories affecting human performance. For example, regarding emotional stress,
Adam and Van Wieringen (1988) have shown that worry and emotionality, measured as personality traits, are negatively correlated with proficiency in a simple motor task. Cognitive stress, resulting from the need for coordinated multitasking in nearly all daily activity, is perhaps the most common stress condition.
Heightened mental load resulting from multitasking typically slows responding, although it often has little affect of accuracy of performance (Castiello & Umilta,
1988). Physical stress is particularly interesting in the light of the contemporary concern with the quality of the natural environment. Urban areas in particular present stressors in the form of noise, air pollution, and disturbance of natural light/dark rhythms. But research has presented an unclear picture of the effects of these stressors, sometimes reporting significant detrimental effects on performance and health and sometimes reporting no effect (Nivison & Endresen, 1993; Smith,
1991). Interestingly, Van Gemmert and Van Galen (1994) showed that performance in a complex sensory-motor task was more sensitive to cognitive stress, manipulated by concurrent memory load, than to physical stress, manipulated by sound pressure level. These often conflicting results argue for a more comprehensive study of stress effects on human performance and for an integrative theoretical framework in which to organize the empirical evidence.
This effort might profitably focus on the nature of the task to be performed and the strategies people use to contend with conditions of stress.
Theories of Stress and Cognition
In general, theories of stress account for its effects on cognition and on human performance in terms of multiple psychological and biological processes.
These processes include, but are not limited to: arousal or activation (stress intensity is directly and linearly related to arousal level), attention allocation
(stress controls directly or indirectly the distribution of attention across points of environmental and internal input and can overload attentional capacity), and plans or strategies for the deployment of attention and other resources. Theories differ
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in their assumptions about these processes. Some attribute little or no role to consciousness or awareness, asserting that stress effects are direct, automatic, biological, or intuitive. Others assign the major performance control functions to plans, appraisals, analyses, and other cognitive phenomena that are invoked in stressful situations. These differences are illustrated in the following section, which presents a sampling of recent theoretical writing on the relationship between stress and cognition.
Cognitive Continuum Theory. Hammond (2000) introduced what he calls a missing link in modern stress/cognition research, that is, a comprehensive set of principles under which stress effects can be classified, interpreted, and coherently integrated. Such a set of principles, if it can be articulated and agreed to, would be tantamount to a new theory and constitute a model for future research in the area.
To set the stage for his theory, Hammond argues that the field has been characterized by two points of view regarding the proper focus of research (for a related argument, see Gigerenzer, Todd, and the ABC Research Group, 1999).
The Coherence point of view incorporates models based on the assumption that human behavior is always contingent not only on the task at hand but also on intervening rational or quasi-rational thought processes. Models of this type include those based on statistical decision analysis, heuristics and biases, information integration theory, and the notion of multi-attribute choice. The coherence position leads to a research focus on the systematic interplay between a task or problem, thought processes it might elicit, and the eventual response. The
Correspondence viewpoint incorporates models that are indifferent to intervening cognitive processes and that focus on systematic and direct relationships between task characteristics and responses, e.g., the empirical accuracy of a judgment. The theories cited as examples by Hammond are signal detection theory, probabilistic mental models, and the author’s work on social judgment theory. The first approach emphasizes analytical cognition (deliberate cognitive processes) and the second approach emphasizes intuitive cognition (unconscious,, non-traceable cognitive processes) (see also Gigerenzer, Todd, & the ABC Research
Group,1999).
Hammond’s theory of judgment and decision making -- the Cognitive
Continuum Theory (CCT) -- is based on four principles, arising from the correspondence and coherence metatheories and two theoretical terms, called intuition and analysis. Of further importance to this theory is the postulate that
“tasks” are special concepts in and of themselves and have properties—“task properties” – that significantly interact with cognition. CCT requires the development of indices to codify both task properties and cognitive properties.
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This is accomplished by considering cognitive activity to lie on a continuum from intuitive to analytical with a mid-point of “quasi-rational thinking” or “common sense”. Tasks are likewise considered in light of their “capacity to induce intuition, quasi-rationality, or analytical cognition”. This then produces a 3X3 matrix of task and cognitive properties onto which a particular cognitive event can be mapped
COGNITIVE
INDEX
INTUITIVE
QUASIRATIONAL
ANALYTIC
TASK CONTINUUM INDEX
INTUITIVE
QUASIRATIONAL
Best
Best
ANALYTIC
Best (normal)
Stress is introduced into this model as a consequence of a disruption of
“constancy” or balance or homeostasis between cognition and task (environment).
Hammond proposes that all organisms seek to maintain stable relations within their environment and the disruption of stabilized relations produces what we know as stress. Stressors are divided into endogenous (any negative change within the task system, e.g. loss of an information source) and exogenous disruptions (those due to factors outside the task system (e.g., fire, noise, cold).
The particular disruption (exo- or endo-) will, according to Hammond, affect the type of cognition and the consequences of judgment. Overcoming endogenous disruption of constancy demands cognitive change, i.e., moving along the 3x3 matrix, whereas overcoming exogenous disruption of constancy demands resistance to cognitive change and staying within the correct cell of the matrix.
How to know when to “change” or when to “stay” within a particular cognitive mode becomes the crux of effective problem solving, leadership, and judgment.
The author contends that not only is this model highly researchable, but should also lead to methods of training that may be different for those being groomed for leadership roles.
Hammond claims that CCT provides a new orientation for the field of stress and cognition. He highlights four points: (1) Environmental events and cognitive events share equal and joint billing in the determination of behavior. (2) Stressors should always be examined in relation to cognitive activities. (3) Disruptions of homeostasis should be differentiated into endo- versus exogenous and the current cognitive mode recognized (intuitive/analytical). (4) Leaders and followers should
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be taught to be alert to and to accept the need for cognitive change. According to
Hammond (2000), these principles provide a cohesive and coherent framework for organizing what we presently know about stress and cognition and the direction that future research in might take.
Theories of activation and resource allocation. Many theories of stress incorportate two mechanisms, one related to activation of the organism and the other related to resource competition. The first mechanism is typically assigned a facilitating effect generally describable as a “readiness to respond.” The second can have a negative effect resulting from the necessity to spread cognitive or other resources thinly over various input and response possibilities. The combination of these two mechanisms allows the theorist to account for the sometimes paradoxical facilitative and inhibitive effects of the same stressor on performance. Facilitation occurs when the activation process dominates; inhibition when the competition process dominates. Facilitation generally occurs under mild to moderate stress and with simpler task requirements. Inhibition occurs at higher levels of stress and more demanding task requirements.
The form attributed to these mechanisms differs widely among theorists. A recent example is Van Gammert and Van Galen (1997), which is described here not because it is the most convincing theoretical argument but rather primarily for purposes of illustration of recent theoretical developments regarding processes underlying stress. Van Gammert and Van Galen employ the concept of neuromotor noise to explicate the activation side of stress effects. But they also incorporate resource allocation and postulate ways in which activation and resource allocation interact.
Van Gammert and Van Galen assert that the human cognitive system is inherently noisy. But increased processing demands produce even larger levels of noise and consequently decreased signal to noise ratios in the system. That stress generates noise in the cognitive system is not a new idea, being first introduced by
Mandler (1979). But Van Gammert and Van Galen develop the idea beyond earlier theoretical statements. According to Van Gemmert and Van Galen, the effects of noise can appear either in effectively reduced sensitivity to task related sources of information or on the motor side in the form of less exacting movements. Van Galen, Van Doorn, and Schomaker (1990), for example, showed that, as the complexity of the sequence of movements required by a task increased, the contribution of tremors and other indices of neuromotor agitation also increased, resulting in a relative degradation of performance. But not all effects of noise are negative. Noise is also said to have an activating or altering
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function. Performance is assumed to be best at optimal levels of signal to noise ratio. Performers engage in various strategies to achieve these optimal ratios.
One strategy is to slow down, permitting noise activation to level off relative to task-relevant activation. Evidence in support of this strategic maneuver comes from classical stress management techniques and from the considerable literature showing among other things that RTs to weak signals are typically slower than
RTs to stronger but otherwise equivalent signals (e.g., Tanner & Swets, 1954). A second stress management principle states that, under conditions of stress, performers adaptively set motor system parameters to produce optimal signal-tonoise ratios for muscles and movement.
Noise effects, when they occur in resource pools, can adversely affect all concurrent tasks drawing on those pools. Noise propagates in the cognitive system such that concurrent tasks are more affected by noise than are independent or sequential tasks. Further, the more closely related two or more concurrent tasks are, the greater the competition between them for resources. A potentially useful extension of this work has been provided by Neufield (1999), who developed a nonlinear formalism for describing multiple variables interacting over time, as in stress and performance.
Van Gammert and Van Galen (1997) tested some of these theoretical ideas in a series of experiments using both verbal (writing numbers in response to dictation) and spatial (aiming and drawing) tasks. Both tasks were performed under two types of stress, cognitive (performing a secondary arithmetic task) and physical (presence of a loud auditory noise). Three measures of performance were taken. Response initiation time, that is, time between stimulus and the beginning of movement, was used as an index of the difficulty of information processing. Movement time, that is, time to execute a response, was used as an index response difficulty. Hand pressure on manipulanda was used to measure tremor and motor stiffness. Both facilitative and inhibitory effects of stress were observed on initiation and movement time. Predictions from theory about resource competition, tremor interference, and time management were largely confirmed by these experiments.
Matthews and Desmond (1995) argue for a model of stress that incorporates three general mechanisms through which stress and the operation of complex systems may interact to affect performance, generally detrimentally. These are (1) overload of attentional capacity, (2) disruption of executive control of selective attention, and (3) disruption of adaptive mobilization of effort. These mechanisms were validated by Matthews and Desmond with data from driving simulator
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studies of stress and dual-task performance. Stress was investigated both through the experimental manipulation of certain environmental variables and the through measurement of individual differences in stress vulnerability. Variables that accentuate detrimental effects of stress include older age, inexperience at the task, and poor attentional skills. The results clearly support the role of attentional resource allocation as the major process mediating stress effects on performance.
The major limiting variable that is most clearly subject to the influence of training is inexperience. Indeed, providing experience with the task and the stressors that occur in it override the influence of age and attentional skills. These data have been taken to support the use of over-training as a countermeasure to stress.
A constraint. Hancock and Warm (1989) point out an important constraint that a general theory of stress and cognition will have to accommodate, namely, that various sources of stress from the environment don’t all impact performance in the same way. Conversely, the same stressor might be reacted to in different ways by different performers. Hancock and Warm examine, in particular, the differing effects on sustained attention of acoustic stress or noise in contrast to the performance patterns that emerge from the influence of heat stress. They note that the task itself, in this case vigilance, can be its own source of stress, and that an integrated view of stress and performance must consider the task as a primary influence in the generation of stress. This assertion is consistent with the role assigned to tasks in Hammond’s theory (2000). Any theory of stress must accommodate these multiple source of stress and their potentially non-additive effects of performance.
Conclusions
There is no shortage of theories about stress and it is impossible to review them all here.
Fortunately, there are a few common themes among these theories and this fact provides a way to categorize theoretical ideas. Some theories emphasize the biological consequences of stress, treating behavior as a by-product of biological processes. Examples include automatic neurological and/or hormonal changes that are triggered by an event. Others focus on the behavioral consequences of stress and on cognitions that mediate the stress/behavior relationship, including importantly how the “stressful” event is appraised by the organism. In general, theories account for stress effects on cognition and on human performance in terms of multiples of processes. These processes include, but are not limited to: arousal or activation (stress intensity is directly and linearly related to arousal level), resource allocation (stress controls the distribution of mainly attentional resources across points of environmental and internal input and can overload attentional capacity), and plans or strategies. Theories differ in their assumptions about these processes. Some attribute little or no role to consciousness or awareness, asserting that stress effects are direct, automatic, and intuitive. Others assign major performance control functions to plans, appraisals, analyses, and other cognitive phenomena. No theory that we have
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reviewed completely elucidates the stress process, and it is only reasonable to expect further attempts at theoretical explication is the future.
Arousal and Performance.
Arousal, alertness, and activation are terms used in the psychological literature more or less synonymously to describe a particular state of the organism.
Like any state, arousal is capable of variation in time. As an organism becomes more aroused, it likewise becomes more alert and more highly active, at least up to a point. Using a circadian analogy, sleep or initial wakening lies at the low end of the arousal continuum. The stimulation or sensory experiences attendant on waking enhances arousal level, and arousal level grows as daily events transpire.
Generally people experience the highest normal levels of arousal around mid-day, although meals can cause transitory decreases and unanticipated events can cause transitory increases or decreases in arousal during the day. Arousal levels decrease with prolonged work and attendant fatigue. The onset of darkness is associated with a return to resting levels of arousal as an individual prepares for sleep (see,
e.g., Neri et al., 2002).
Human performance in nearly all situations tends to be correlated with arousal, improving up to a point as arousal level increases and falling off as arousal decreases diurnally. But there are, of course, many qualifications on this general rule. For example, arousal level can become too high for the task at hand. When a person is over-aroused, performance will deteriorate. Moreover, simple tasks like vigilance, time estimation, or the execution of a single well-practiced manual response are performed optimally under relatively high arousal levels, whereas complicated tasks such as those involving a sophisticated level of mental calculation are performed optimally under relatively low levels of arousal. Thus, it has been known for some time that modestly increasing a person’s level of arousal,
e.g., by introducing the threat of a painful stimulus, facilitates performance on a simple task like time estimation (e.g., Falk & Bindra, 1954), but can hinder performance on more complicated tasks like public speaking or mental arithmetic
(see Giesbrecht, Arnett, Vela, & Bristow, 1993; Lovallo, 1997).
The correlation between arousal and performance is so ubiquitous that it has come to be accepted as a law in psychology – the Yerkes-Dodson (Y-D) law, named for its putative discoverers (Yerkes & Dodson, 1908). The law takes the form of an inverted U-shaped relationship between performance and arousal.
Performance on any task is best at some mid-level of arousal, falling off as arousal becomes too low or too high. The specific level of arousal that is optimal for
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performance differs among tasks, tending to decrease as task difficulty increases.
The lawful status of this relationship was solidified by Donald Hebb in his oft-cited presidential address to the American Psychological Association (Hebb, 1955).
Despite the intuitive reasonableness of this relationship and the vast amount of empirical support for it, there has been some skepticism. Hancock (1987), for example, pointed out that the Y-D law borders on the tautological, given that the result it expresses could hardly be otherwise. That is, performance in any task is bound to be poorer when the performer is under- or over-aroused. Some mid-level optimum follows necessarily. This controversy is irrelevant to present purposes, however, because we interested only in the descriptive feature of the Y-D “law.”
Motivation and Arousal
Arousal might affect performance simply by activating response systems.
An aroused organism is an organism that is ready to respond. Whether the activated response systems are relevant or correct for the task or irrelevant or incorrect determines whether arousal facilitates or impedes task performance. An alternative theory (see Lovallo, 1997) links arousal to motivation. The more aroused the organism is, the more it is motivated to perform well. Such a theory accounts easily for the initial upward leg of the Y-D law but requires interference or inhibitory processes to account for the possibility that an organism can be “too motivated” to perform well. Among the models that have been suggested are those that invoke activation of competing responses at higher levels of motivation
(Lovallo, 1997). Even though there might be a strong link between arousal and motivation, there is plenty of evidence that these are separable concepts. For example, Dyregrov, Solomon, and Fredrik (2000) have shown that performers can counteract the potentially degrading effects of supra-optimal levels of arousal by extra effort. Making an extra effort is surely a matter of motivation, which means that, in this example, motivation competes with arousal for control of behavior.
Countervailing influences imply unique and separable motivational and arousal processes. Stress and Arousal
Stress effects on performance are, in part and to some extent, mediated by arousal. Like arousal itself, stress can have either beneficial or degrading effects on performance, depending on the intensity of the stressor, the momentary level of arousal when the stressor occurs, the nature of the task to be performed under stress, the skill of the performer, and other variables. Light stress introduced while the participant is at some sub-optimal level of arousal has been shown to facilitate
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performance (e.g., Bourne, 1954; Falk & Bindra, 1954: Meyer, 1953; Spielberger,
1966, 1972). But one unique and important feature of stress is that it can induce high levels of arousal that are rarely seen in normal circumstances. Thus, often, stressors induce levels of arousal beyond optimal for performance in any task, and as a consequence, performance is degraded. Modest levels of supra-optimal stress can be counteracted by the performer by increased effort, resource mobilization, or straining (e.g., Dyregrov, Solomon, & Fredrik, 2000; Gaillard, 1993; Gaillard &
Wientjes, 1994; Hocket, 1997; Matthew, Sparkes, & Bygrave, 1996). Razmjou
(1996; see also Razmjou & Kjellberg, 1992) claims that resource mobilization involves deliberate processes, basically strategies for controlling effort, that allow the performer to adapt to the source of stress or arousal and to task demands.
According to Hockey (1997), successful performance in any task requires the operation of a control mechanism, which allocates resources dynamically.
Performance may be protected under stress by the recruitment of previously untapped resources, but only at the expense of increased subjective effort, and other behavioral and physiological costs. Of course, performance stability can be achieved by reducing goals, without further costs.
At some high level, however, stress will degrade performance. Under the pressure of an emergency, close examination by others, time urgency, threat of bodily harm, or other strong stressors, people often falter. Performance degrades, or worse fails. At the extremes of stress, a performer might “choke” or “panic.”
Stress States: Qualitative Effects of Stress
Quantitatively, stress effects on performance follow the inverted U-shaped relationship (the Y-D law). Although there is considerable evidence in support of such a relationship, the Y-D law is not the whole story and has limited explanatory value for a variety of reasons (e.g., Hancock, 1987). For one thing, not all empirical evidence is consistent with a U-shaped function of performance across levels of arousal (Westman & Eden, 1996). Secondly, as Hockey (1983) and
Hancock and Warm (1989) argued, every stressor produces its own unique pattern of effects on cognition and performance, making it unlikely to find an adequate allencompassing principle or theory. Further different stressors can interact, often producing nonadditive effects on performance (e.g., Hygge & Knez, 2001). Evans,
Allen, Tafalla, and O’Meara (1996) examined the interactive effects of multiple, sequential stressors on cognitive performance and psycho-physiological indices.
Subjects engaged in a relaxing or a highly stressful activity followed immediately by performance of a task under quiet or noisy conditions. Results indicated that the negative effects of noise on both concurrent and aftereffect performance and on BP
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were exacerbated by prior exposure to either a lab stressor (making a speech) or to a naturalistic stressor (college final examination). Thirdly, the Y-D law relates only to arousal or system activation and not to other processes such as interference and resource demands that might also be influenced by stress. Finally, and perhaps most importantly, Y-D law relates exclusively to simple quantitative measures of goodness of performance, e.g., speed or accuracy of response.
It is clear that stress creates qualitative changes in the organism and its performance, above and beyond those captured by the Y-D law. For example, at some point, stress increments begin to degrade performance. Initial degradation is graceful, that is, small and gradual reductions in performance as stress increases.
In extreme circumstances, the degradation in performance can be catastrophic, with a stress increment causing a complete system failure (Norman & Bobrow,
1975, 1976). Different stressors and different levels of stress act upon cognitive functions through different intervening states. There is need in a complete account to develop a descriptive or explanatory system that reflects these qualitatively different states.
We suggest that the concept of Stress State will help to elucidate the various
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ways in which stressful circumstances and feelings of stress influence human performance. The Stress State figure shown above serves as a useful guide to these effects. As previously noted, stress at low levels creates a state of facilitation.
Chappelow (1989) was able to show in an analysis of aircrew errors that cognitive failures are often associated as much with under-arousal as they are with overarousal. He found that performance actually improved with a little stress in the environment. At some point, stress for a given task and individual reaches an optimal state or level. Performance can be maintained at supra-optimal levels of stress if the performer can summon a higher motivational state, sometimes called a state of strain or mobilization (see, e.g., Doerner & Pfeifer, 1993). But, as stress increases even further, performance will eventually enter a state of degradation, and the performer will find him or herself less capable of adequate responding.
Performance degrades, but in a relatively graceful manner (Norman & Bobrow,
1975). Extreme levels of stress produce more than simple or graceful degradation in performance. Eventually, the effects of stress can become catastrophic. A experimental example of catastrophic performance degradation with stress, resulting in a choking or panic state, can be found in Lehner et al. (1997), These researchers reported that, with extreme time pressure, subjects stopped using decision making procedures they were instructed to use and reverted to more familiar, more intuitive procedures, even though these procedures resulted in inferior performance. These qualitatively unique stress states are not captured by the Y-D law.
It is important to distinguish between choking and panicking, two extreme kinds of performance degradation resulting from stress. Before elaborating on this distinction, consider the following. When you first learn how to do a particular task, like drive an automobile or play tennis, you think through each step in a deliberate and conscious manner. You learn the task explicitly and your representation of the task lies in an array of explicit memories. But, as you train more and improve on task, responses become more automatic and come to require less and less thought or attention. Performance becomes more fluid and skillful and is often conscious only in retrospect. The learning at this point achieves an implicit status and the representation of learned skill resides in implicit memory.
What you know about any task you have learned and practiced typically has representation in both an implicit and an explicit memory system.
Choking is a form of performance degradation that involves an unintentional transition from well-learned, highly practiced, essentially automatic action to a more time consuming, controlled form of responding. This is a transition that changes the basis of responding from an implicit to the explicit memory system.
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The consequence of this transition is often inferior, or at least slower performance.
Stress sometimes induces this transition, and that is what is meant by “choking under pressure.” When you revert to thinking about each step required by a familiar task, you lose your fluidity. You begin to perform slowly and cautiously, much as you did when just starting out to learn the task. You become a beginner once again and often perform like one, relying on memories that often have not been used in quite awhile. You are “overthinking” the situation. In sports, this is what coaches mean when they use the stock phrase “paralysis by analysis.” A player or the team fails because of over-analyzing the situation, rather than simply reacting. In one of a very few laboratory studies of choking, Beilock and Carr (2001) investigated the performance of golfers. One group of participants was trained to putt a golf ball with a video camera set up in front of them, under the instruction that professional golfers would review and critique the tapes. This condition was designed to adapt golfers to being in the spotlight, raising their self-consciousness and increasing their attention to their own performance under scrutiny. A second group was trained while listening simultaneously to a list of recorded words, under the instruction to repeat the word “cognition” whenever they heard it. This condition was intended to adapt golfers to being distracted while trying to putt. A third group was trained under quiet, nondistracting conditions.
After extensive practice designed to develop a high level of putting skill, participants took a test under both low- and high-pressure conditions. The idea was to determine whether training under distracting or self-focus conditions would improve golfers’ ability to perform better under pressure than normal training conditions. In other words, if you focus less than you normally would on the task at hand, which might happen when distractions are present, or if you focus more on the task, which might happen with greater self-awareness, does your performance under pressure suffer? In the low pressure test (no secondary task, no video camera, no audience), all three training groups performed equally well. In the high pressure test, in which a significant amount of money was contingent of excellent performance, the normal and the distraction training groups were significantly inferior to the self-monitoring group and performed worse than they had during training. The self-monitoring group actually performed better on the test than they had during training.
People under pressure are more stressed, anxious, and aroused and more self-conscious about their performance. Consequently, they try to exert greater conscious control over their actions, rather than allowing the skill they had
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acquired to guide their performance implicitly. There are numerous examples of choking due to heightened self-consciousness or other stressors in the sports literature and folklore, e.g., Greg Norman’s collapse in the final round of the
Masters’ Golf Tournament in 1996 or Jana Novatna’s last set loss to Steffi Graf at
Wimbeldon in 1993. Beilock and Carr (2001; see also Beilock, Carr, MacMahon,
& Starkes, 2002) argue that training in an environment in which one is forced to attend to performance from the outset can immunize the performer against the negative effects of pressure. Golfers in the self-monitoring group were protected from choking because, during training, they had adapted to the impact of conscious self-awareness and were able, unlike participants in the other two groups, to rely on implicit procedural memories to guide their performance. They were better able to “go with the flow,” undeterred by extraneous stressors. Without such training, choking is a possible consequence of intense social, competitive, or other pressures. Panic is a different stress state, and typically results in a more severe form of performance degradation than choking. When panic occurs, behavior becomes primitive; if the person thinks at all, it is maladaptive automatic thinking (Katz &
Epstein, 1991). Panic is not just a matter of reverting to behaviors that had been learned earlier or to memory representations in an explicit form. Panic is characterized by an even more rudimentary, instinctive kind of behavior aimed at survival. Rather than “overthinking” the situation, a panicked person stops thinking altogether and is inclined to react in the most basic way to get out of the situation or to escape the stressor. Stress appears to cause explicit memories to become unavailable or irretrievable. In a panic state, short-term memory seems to cease functioning. The person just freezes, that is, fails to respond, responds in an automatic but unskilled way, or reverts to primal instincts . Moreover, high arousal, as under stress, results in perceptual narrowing (Easterbrook, 1959). The range of cues or sources of informational input that an organism might use to escape the situation is reduced. The panicked individual focuses, indeed often obsesses on one aspect of the environment, usually to the neglect of information that could eliminate the stressful condition. The consequence is that, even though the goal is survival, performance is functionally maladaptive (Katz, & Epstein,
1991). To use another bit of sports jargon, coaches have been known to refer to a state of panic as “brain lock.” The cognitive performance system is locked down.
Conditions of panic are virtually impossible to create in the cognitive psychology laboratory. Thus, most of what we know about panic under stress comes for case histories and self-reports. Good examples come from SCUBA diving and sky diving. Skydivers have two parachutes and are trained such that, if
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the primary chute fails to open, they should immediately pull the cord on the secondary chute. There have been reported accidents resulting from a failure to do so. People have been found dead or injured on the ground still clutching the cord to the primary chute. Apparently, these victims pulled the cord for the primary chute and, when it failed to open, panicked, continued to tug, but never thought about the secondary parachute. Other poignant examples from piloting can be found in Langewiesche (1998).
Panic is clearly a state to avoid, if one is to escape an emergency situation.
The question is, can we develop training routines that minimize the likelihood of panic in situations that are susceptible to emergencies. On the basic research side, we need to develop experimental paradigms, building on the work of Beilock and
Carr, that permit the establishment of choking and panic states under laboratory conditions. There seems to be little evidence of that possibility at this writing.
Conclusions
There is a close relationship between stress and arousal. Stressful events are arousing, causing attendant changes in states of the organism, in cognitive processes, and in performance.
Of greatest relevance to behavior in emergencies are the stress states of (1) strain or mobilization, wherein the person recruits untapped resources to maintain performance levels when arousal is supra-optimal, (2) degradation, wherein mobilization fails and performance suffers but only gradually, (3) choking, wherein performance might fail as the organism overthinks the tasks at hand, and (4) panic, wherein performance reverts to non-cognitive primitive modes of behavior. Research has established the basic parameters of these states, but little is known in detail about situations and individual differences that are conducive to them or about the cognitive difference among them. This fertile ground for future empirical research.
Appraisal
Lazarus (1990; see also Lazarus & Folkman, 1984) developed a comprehensive cognitive model of behavior in response to stress. That model is based on the fundamental assumption that a potentially stressful life episode does not actually create stress unless it is appraised as threatening. That is, the ways people think about situations determine how they respond emotionally and how they cope with those situations.
As reasonable as it might sound, many of Lazarus’s postulates have received little empirical attention, and some of the existing research has yielded contradictory findings. For example, Zakowski, Hall, Cousino-Klein, and Baum
(2001) conducted a longitudinal study to clarify the associations among feelings of
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control, appraisal, coping, and stress. Lazarus’s theory postulates that coping strategies tend to match the level of appraised controllability of the stressor
(matching hypothesis). Recall that Hammond’s (2000) theory contains a related postulate to the effect that a match between strategy and task renders a situation non-stressful. An alternative to Lazarus’s expectation is the main-effects hypothesis, which states that problem-focused coping is generally more effective in reducing distress regardless of appraisal. These hypotheses were tested by
Zakowski et al. with 72 adults who completed questionnaires on coping, control, and appraisal. Stress was assessed using both a self-report and a behavioral measure at two different times approximately 2 months apart. The matching hypothesis was consistent with both self-report and behavioral measures of stress, giving some of the strongest evidence for appraisal theory yet reported.
Mathews and MacLeod (2002) argued that appraisals can be readily induced or changed by laboratory manipulations. Induced biases (or appraisals) affect felt anxiety when they influence how emotionally significant information is encoded by a participant. Biases and appraisals affect vulnerability to anxiety via their influence on how stimuli are processed or interpreted. Mathews and MacLeod argued that it is relatively easy to set someone up for an anxiety attack by giving him or her the right orientation toward or appraisal of up-coming events or information. The cognitive appraisal model also predicts that a person’s interpretation of an event affects the intensity of his or her reaction to it. A study by Zohar and
Brandt (2002) shows that, in cases involving a variety of possible stressful factors, the most salient stressor governs appraisal, not the summation of stressors or any other interaction of stressors. The condition perceived to be most important captures attention and takes control of how the person appraises and subsequently responds to the situation.
Anticipation of a stressful event, such as a parachute jump or piloting a plane, often includes a great deal of uncertainty. There might be a large number of unknowns, and emotions can range from extreme negative (worry, fear, anxiety) to positive (hope, eagerness, exhilaration). Skinner and Brewer (2002) studied the emotional feelings experienced during this anticipation period by students preparing for a college examination and certain other stressful events, particularly as they relate to the participants’ appraisals of the event as a challenge or a threat.
Compared to threat appraisals, challenge appraisals were associated with better emotion-coping styles, more positive emotional feelings, and greater confidence about performance. Moreover, participants who viewed the up-coming event as a
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challenge performed significantly better on that task. Because coping styles, appraisals, and emotional feelings were established in advance of the event itself, they all appear to have significant roles in mediating or determining performance.
Ennis, Kelly, Wingo, and Lambert (2001) hypothesize that subjects’ appraisal of a task or situation causes differential elicitation of neuro-endocrine activity. They determined that, if a subject sees an academic exam as a threat, sympathetic neuro-endocrine activity (measured in urine) increases before the event, relative to subjects who see the exam as a challenge. During or after the exam, activation drops and there is no difference between the threat and challenge groups in posttest measures. Overall, Ennis et al. found a positive correlation between self-reports of anxiety and adrenomedullary activity. The authors conclude, consistent with Lazarus’s model, that appraisal mediates not only behavior but also certain biological components of the human stress response.
Rohrmann, Hennig, and Netter (1999) used a different approach, but came basically to the same conclusion as Ennis et al. Rohrmann et al. demonstrated that psycho-biological reactions to the stress of public speaking can be manipulated by giving participants pre-speech information regarding how to appraise the state of their body. During an anticipation period before a speech, subjects were given either no information (in the control condition), were given information to the effect that they were psychologically aroused and nervous (in an arousal condition), or that they were psychologically calm and relaxed (in a reassurance condition). Heart rate (HR), BP, cortisol levels, and electrodermal responses were highest in the reassurance condition and lowest in the control condition. Felt emotional stress reactions, in contrast, were highest in the arousal condition and lowest in the reassurance condition. Somatic arousal was greater than felt emotion in the reassurance condition whereas felt emotion was higher than somatic arousal in the arousal condition. The authors concluded that different appraisals and consequently different coping styles were induced by pre-training. The arousal condition induced a coping style that sensitizes the subject to the state of his or her body; in contrast the reassurance condition induced a more cognitive style of stress reduction. In any case, establishing a way of appraising a potentially stressful situation mediated psycho-biological reactions to and performance during the event. Prior to a film depicting three serious factory accidents, Danboy and
Goldstein (1990) instructed some subjects about how to take and maintain a detached attitude – intellectualizing instructions – while others were merely told about the content of the up-coming film. Intellectualizing subjects demonstrated
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less self-reported stress and lower galvanic skin responses (GSRs). All subjects were less accurate on a memory test for accident related as opposed to nonaccident related aspects of the film. Thus, how you appraise the film or the events it depicts controls to some degree the emotion the film provokes, a result which is consistent with Ennis, et al. (2001) and Rohrmann, et al. (1999), although in a different context.
Larsson (1989) reported a study of the performance of Swedish military personnel on an artillery simulator, under conditions of calm, noise, and noise plus
27 hrs sleep deprivation. Apprising the task as a challenge was associated with positive coping and better performance, relative to a threat appraisal, under all conditions. But performance degraded with increased stress and negative coping increased with increased stress. Those subjects who were high in achievement motivation were more likely than those subjects who were low in achievement motivation to appraise noise and sleep deprivation as challenging and to use coping strategies that were positive and action oriented. Positive coping strategies tended to counteract the adverse effects of stress. Similar results were reported with college students by Wallbott and Scherer (1991).
Conclusions
There is a fair amount of agreement in the current literature on appraisal and stress. First, cognitive appraisals play a significant mediating role in biological reactions to stress. Second, performance outcomes depend in part on whether the subject appraises the situation as a challenge or a threat. Third, appraisals tie into coping styles such that challenges are associated with positive and more successful coping styles whereas threats are associated with negative styles. But the picture is not completely clear. It might be that, in all the experimental situations explored to date, more competent people are more likely to view any situations as a challenge rather than a threat. If this is the case, then better coping and better performance naturally follow from challenge appraisals. Because, as yet, no one has been able to create a way of separating conceptually appraisal from competence, we are left with basically a correlational result and without a clear picture of the cause-effect relationships that are involved.
Attention and Perception
It is clear that stress, especially acute stress, has important effects on attention and perception. But the effects are quite irregular, and depend in serious ways on the qualitative features of the stressor. Different stressors have different effects on performance. One stressor might cause shifts in attention or a failure to inhibit irrelevant stimuli, while another stressor causes a lapse of attention or attentional narrowing in the same task.
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Inhibition and Attention
Given that the effects of stress on attention can be unpredictable, still there are some results that are general, systematic, and reliable. One example is the latent inhibition (LI) effect. Pre-exposure to a stimulus reduces the utilization and the learning of that stimulus on some later occasion. This LI phenomenon is typically attributed to a reduction in attention to stimuli caused by their preexposure in another task. When stress is present in the learning or test phase, however, latent inhibition is reduced or eliminated. Attention to the stimulus is not affected by pre-exposure and learning involving the pre-exposed stimulus is as good as if the stimulus was novel. Stress was induced in one experiment
(Braunstein-Bercovitz, Dimentman-Ashkenazi, & Lubow, 2001) by threats to selfesteem in a difficult number series completion test said to be related to intelligence. In a second case studied by the same authors, the LI task was described as a part of the selection process to job seekers. LI was attenuated in both experiments in high as opposed to low stressed subjects. Thus the results show that stress impairs the inhibition of irrelevant pre-exposed stimuli.
Is proneness to anxiety associated with impaired inhibitory processing?
Participants in a series of experiments reported by Wood, Mathews, and Dalgleish
(2001) made speeded decisions which required inhibition of the meaning
(threatening or neutral) of ambiguous words. Under normal conditions, they found that anxious and non-anxious participants perform equally well in this task.
However, when a mental load was induced to reduce controlled processing, anxious subjects did not inhibit word meaning as well as non-anxious subjects. In a final experiment, attenuation of inhibition was demonstrated even without mental load in subjects who had recently experienced a traumatic event.
Keinan, Friedland, Kahneman, and Roth (1999) reported similar stress effects with both college students and navy personnel using a variety of cognitive tasks, including arithmetic, estimation, number series, and analogies. In the number series and analogies tasks, both of which required the inhibition of competing responses, but not in the other tasks, performance was poorer in the high than in the low stress condition. These authors concluded that stress heightens the difficulty of suppressing or filtering out competing responses.
Mogg, Bradley, and Hallowell (1994) tested high and low trait anxious students for attentional bias to threat stimuli (words) under no stress, laboratoryinduced stress, and natural examination-induced stress. High anxious subject
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showed an attentional bias toward threat words, but only when those words were presented for long duration, without a mask, and under examination threat.
Anxiety sensitized the subject to threat mainly when the induced anxiety is somewhat protracted.
Measured levels of stress hormones are consistent with the abovedemonstrated effects of stress on inhibitory processes. Skosnik, Chatterton,
Swisher, and Park (2000) induced mild stress into the verbal priming paradigm using a video game. Stress reduced negative priming, a measure of inhibition processes, and also increased salivary cortisol and alpha-amylase (a correlate of norepinephrine). So, both chronic anxiety, as in trait anxious subjects, or acute anxiety, as in trauma, is associated with a general deficit in inhibition of attention, and is best revealed when limitations are placed on controlled processing, forcing subjects to rely more heavily on automatic reactions. Behavioral and physiological measures are consistent with changes induced by stress on inhibitory processes. These results imply that, in a natural emergency, when stress is high, there is need to be concerned about an operator’s ability to focus on the relevant information in the task at hand and to inhibit irrelevant sources of input.
Perception and Cue Utilization
Based on a review of the early literature on arousal and attention,
Easterbrook (1959) concluded that stress, anxiety, or high arousal can narrow the range of environmental cues utilized, shrinking one’ effective perceptual space.
This idea has been expanded by Cowan (1999) in a theoretical analysis of working memory. Among other things, Cowan draws a sharp distinction between attentional processes, which in his view are basically capacity-limited, and working memory, (the activated portion of long-term memory in his theory), which is basically time-limited. Thus, consistent with Easterbrook, Cowan predicts that the effects of stress on attention are to limit its scope or content. People attend to and process less perceptually-available information when they are stressed. In contrast, the effects of stress on memory are to limit its time extension. Such an expectation is consistent with the memory constriction hypothesis that we develop in this report. Since Easterbrook’s publication, there have been numerous demonstrations of an attentional deficit under stress, in and outside of the laboratory. For example, Ozel (2001) found that time pressure and the stress created by the threat of fire affects how people process information provided to them about the right route to take to escape. Slight stress was beneficial to escape
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performance, but higher levels of stress narrowed the range of environmental cues attended to or processed and increased the use of negative coping styles by participants. Escape performance suffered as a consequence.
Vigilance
Performance in a vigilance task, which requires the detection of infrequent stimuli, degrades in time, a phenomenon known at the vigilance decrement (Mackworth, 1950). Galinsky, Rosa, Warm, and Dember (1993) observed that restlessness and subjective fatigue, both indices of stress, increased dramatically across a 50-min watch in a vigilance task in which sensory modality of signals (audition and vision) and the background event rate (5 and 40 events/min) were varied. Stress effects were most notable in the case of visual monitoring but were unrelated to variations in event rate. Thus, the stress of sustained attention seems to be identified more specifically with the sensory modality of signals than with the event rate context in which they appear. Temple, Warm, Dember, Jones,
LaGrange, and Matthews (2000) observed that 30 mins or more of sustained vigilance produces not only a performance decrement, but also increases in felt workload and stress. Stimulant drugs, like amphetamine sulphate or caffeine, extraneous auditory stimuli, and other arousing agents should enhance vigilance and counteract the deterioration in vigilance performance that occurs with the passage of time. Temple et al. (2000) found evidence that ingestion of caffeine during the task improved vigilance and signal detection but did not reduce task-induced stress.
Lavine, Sibert, Gokturk, and Dickens (2002) examined concurrent eye movements and human performance during a vigilance task designed to require frequent visual scanning. Stimuli were 4 digits in a rectangular array, changed at an event rate of 4 s for a task duration of 30 min. Participants were asked to respond to specific, infrequent signal arrays by bar press, under both 50 dBA white noise and
90 dBA intermittent and unpredictable sound-burst conditions (SBC). With timeon-task, subjective fatigue ratings increased, the total duration of fixations on target digits decreased, number of fixations decreased, and fixations were further from target digits in both conditions. Thus, the usual vigilance performance decrement was replicated. Fixation duration did not change significantly with time or condition. Off-target visual scan-paths were less frequently followed by hits than were on-target scan-paths in both conditions. With the SBC, fixations were closer to target digits and hit rates increased, suggesting that background stimuli with a potential alerting function can help to offset the vigilance decrement.
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Conclusions
Both chronic anxiety, as in trait anxious subjects, or acute anxiety, as in trauma, produce a general deficit in a person’s ability to inhibit irrelevant stimuli. The effect is most clearly revealed when limitations are placed on controlled processing, forcing subjects to rely more heavily on automatic reactions. These results imply that, in a natural emergency, when stress is high, there is need to be concerned about an operator’s ability to focus on the relevant information in the task at hand and to inhibit irrelevant sources of input. This effect of stress on inhibitory processes is similar to and likely related to Easterbrook’s finding that the range of cues perceived and attended to shrinks under stress or high arousal. Other evidence shows that the ingestion of stimulants can be effective in offsetting the vigilance decrement as can the aperiodic occurrence of irrelevant or background stimuli, if they have some degree of alerting function.
Memory
. As we have noted earlier, cognitive psychology is currently concerned with a variety of forms of memory. One important distinction applies to the temporal character of information retrieved from memory. This distinction is based on a continuum from the remote past – retrospective long term memory – to the present or near present – short term memory and immediate or working memory – to the future – prospective memory. Long-term memory is theoretically a repository for facts and skills acquired in the past. Short term and immediate memory holds facts and skills that are currently at the focus of attention.
Prospective memory contains reminders of actions to be executed at some future time and place. The important variables influencing memory might not the same in all three cases. One variable that seems likely to be influential is stress.
Stress effects have been studied in the context of various forms of memory, although the experimental data available are surprisingly few. There are no data comparing different forms of memory for their relative susceptibility to stress. The evidence that is available seems to suggest that stress, in general (including stress arising in emergency situations), causes the operator to focus on the here-and-now, with consequent potential degradation of retrospective and prospective memory performance. The results are consistent with a memory constriction or tunneling hypothesis to the effect that the time span from which knowledge can easily be retrieved and used in a given context shrinks as stress level increases. Neglect of facts or procedures in long term memory, and failure to execute required behaviors at appointed future times is a major reason for performance errors or failures in emergencies. Although memory tunneling has been observed in the retrieval of autobiographical events (Berntsen, 2002), empirical evidence to support this broad
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stress/memory hypothesis is weak. The hypothesis could, however, serve a framework for future research efforts.
General Stress Effects on Memory.
As we have shown in other sections of this report, a variety of stressful conditions impede a variety of memory measures. For example, Gomes, MartinhoPimenta, and Castelo-Branco (1999) showed a significant impact of stressful noise on immediate verbal memory. Fowler, Prlic, and Brabant, (1994) reported a similar effect of hypoxia on the executive function of working memory. Mandler
(1979) was one of the first cognitive psychologists to speculate theoretically about the effects of stress on memory. Stress produces noise in the cognitive system, according to Mandler, which competes with task demands for limited cognitive, that is, conscious resources. Recall that a similar proposition about noise in the cognitive system, generated by stress, was made by Van Gemmert and Van Galen
(1997). Thus, in Mandler’s theory, those memory processes that rely on conscious elaboration of input and representations, namely explicit memory processes, should be especially degraded by stress. To date, there has been no clear test of this hypothesis. It is not inconsistent, however, with the memory constriction
(tunneling) hypothesis describe earlier, in the sense that focusing on the here and now necessarily requires explicit memory while longer term recall and prospective recall might not.
As we shall discuss in detail later, Van Overschelde and Healy (2001) have shown empirically that one mechanism for coping with and reducing the stress that information overload engenders is to provide connections between new facts to be learned under stress and an existing knowledge base. The general principle is that the acquisition and retention of new, factual information is facilitated whenever that new information can be linked to existing knowledge. The mechanism underlying this strategic-use-of-knowledge principle is based on the provision of a retrieval strategy supported by factual information that already exists in long-term memory. This idea is an extension of the theory of long-term working memory
(Ericsson & Kintsch, 1995), which has been used, for example, to account for text comprehension and for expert-level performance in memory-span tasks. This is still another hypothesis that should be testable empirically, although it has not been examined in the literature to our knowledge.
Another approach to the role of working memory in the explanation of stress effects is represented by the work of Ashcraft (2002; see also Ashcraft & Kirk,
2001). People with high math anxiety have a reduced working memory capacity
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according to Ashcraft. Because working memory is required by many arithmetic and mathematical tasks, math anxious subjects perform more poorly on these tasks than low anxious subjects. This leads to the prediction that, if working memory can be limited artificially in non-anxious subjects, their performance on calculation tasks should similarly be adversely affected. By introducing a concurrent task with working memory demands or by stretching working memory by primary task demands, Ashcraft was able to show effects on performance similar to those observed in high math anxious subjects. Ashcraft’s conclusion is that stress exerts its effects primarily by reducing a person’s working memory capacity. Such a result, if replicable, might be inconsistent with the memory constriction hypothesis, described above, in the sense that memory constriction implies a greater effect of stress on retrospective and prospective memory than on working memory. Studies comparing various forms of memory under stress are needed to decide between these hypotheses. Any task that requires explicit learning and/or memory processes should be especially liable to stress effects, according to Ashcraft.
Conclusions similar to those of Ashcraft have been reached by Eysenck
(1992, 1997; see also Eysenck & Calvo, 1992). Moreover, in a recent review of research on working memory, Miyake and Shah (1999) identified emotion, stress, and especially anxiety as a major modulating factor of working memory capacity.
They suggest that, in various ways, stress limits the time scope of memory. But, after searching the literature, they concluded that insufficient empirical data have been collected on the problem and recommended further research to identify what aspects of working memory (e.g., maintenance, executive control, content) are influenced by anxiety and other emotional factors. Why should working memory capacity be reduced under stress? Matthews (1996) argues that “worries,” daily hassles, and/or intrusive thoughts tend to occupy more space in working memory among high anxious than among low anxious subjects, limiting the available working memory space in high anxious subjects for the calculations that their primary task requires (see also Dudke & Stoebber, 2001). There is some evidence that a stressful event, itself, can cause lingering intrusive thoughts (see below), but little data at present to support Matthews’s “worries” hypothesis.
A caution. Studies of stress and memory must take account of state and context dependency effects. That is, it has routinely been shown that performance in a retention test is better if the state of the subject and/or the context in which the test is administered are the same as the state and context of original learning.
Although stress might exert adverse effects on both encoding and retrieval processes, there is some possibility that changing the stress state of the organism between the times of learning and retention, from stress to no stress or from no
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stress to stress, will have its own adverse consequences. But, other things being equal, recall performance will be better if tested under the same state, stress or non-stress, as present during encoding. Lang, Craske, Brown, and Ghaneian,
(2001) demonstrated this phenomenon in a word recall task using induced states of both fear and relaxation. But, most studies of stress and memory in the current literature ignore these dependencies, usually testing the subjects’ memory under stress for information or skill acquired under non-stressful circumstances. This is a serious limitation on the usefulness of the current stress/memory literature, and must be corrected in future work.
Memory for emotion-arousing stimuli. There is conflicting evidence in the literature regarding memory for emotionally arousing stimuli. As we noted earlier, most studies have reported that memory is better for either pleasant or unpleasant material than it is for emotionally neutral material. But there are exceptions.
Further, some investigations have, reported that traumatic stimuli, like autopsy photos, can inhibit memory for simultaneously presented neutral material (see, e.g.,
Kramer Buckhout, Fox, Widman, et al, 1991). Whether these differential observations should be attributed to differing methods of presenting materials and measuring memory or to the degree of emotion provoked by the stimulus material is not clear at the present time.
Lang, Davis, and Ohman (2000) attempted to explicate what is special about memory for emotional information, emphasizing the neural foundations that underlie the experience and expression of fear. They proposed that unpleasant emotions depend on the activation of an evolutionarily primitive subcortical circuit, including the amygdala and the neural structures to which it projects. This motivational system mediates specific autonomic (e.g., HR change) and somatic reflexes (e.g., startle response) that originally promoted survival in dangerous conditions. These authors show how variations in the neural circuit and its outputs may separately characterize cue-specific fear (as in specific phobia) and more generalized anxiety. Emphasizing links between animal and human data, these authors focus on certain special, attentional features of emotional processing, including: (1) The automaticity of fear reactions, (2) hyper-reactivity to minimal threat-cues, and (3) evidence that the physiological responses in fear are independent of slower, deliberate language-based appraisal processes. This last difference accounts, in their view, for the special character of and better memory for emotional as contrasted with neutral information.
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Cortisol and other Neuro-biological Considerations..
Cortisol is a stress hormone that readies the body to fight or for flight.
Among other things, cortisol stimulates the secretion of intracellular glucose into the blood, which allows longer and more vigorous and sustained responding.
Although the mechanism is less clear, it is also known that ambient cortisol levels can affect cognition. For example, al’Absi, Hugdahl, and Lovallo (2002) showed that participants who had a large cortisol responses, i.e., acutely elevated levels of cortisol, during mental arithmetic and public speaking tasks, performed better 30 mins later on a dichotic listening task, compared to those who had low cortisol responses. Dichotic listening requires sustained focused attention to external stimuli, and sustained attention is known to engage the executive processes of working memory. Thus, it is of great interest that working memory depends on adequate functioning of the dorsolateral prefrontal cortex (Smith & Jonides, 1999), an area richly supplied with corticosteroid receptors and corticotropin-releasing factor terminals. It has been argued that these studies imply that emotional dispositions, possibly even more than environmental circumstances, are crucial in how one responds behaviorally to stress (Kosslyn, Cacioppo, Davidson, Hugdahl,
Lovallo, Spiegel, & Rose, 2002).
As noted above, there is evidence that stress has effects on both encoding of new memories and retreival of old memories. But what about memory storage, the process of holding memories after encoding for later use in retrieval tests? For several decades, the concept of modulation of storage has significantly influenced research investigating neurobiological memory mechanisms in animals. New evidence provides additional support for the view that stress hormones released during emotionally arousing situations can influence memory storage. Recent experiments have investigated the role of sympathetic adrenomedullary hormones in emotional memory in human beings, as well as the role of adrenocortical hormones, primarily in animal studies. Further, it is becoming increasingly clear that the sympathetic adrenomedullary and the pituitary adrenocortical systems interact to modulate memory storage. Other new evidence emphasizes the role of peripheral influences to the brain on emotional memory, as well as the critical contribution of the amygdaloid complex in modulation of memory by emotional arousal. For a review of this literature, see Cahill and McGaugh (1996).
Glucocorticoids (GCs), produced by the stress-responsive hypothalamicpituitary-adrenal axis, are well recognized for their regulatory role in peripheral metabolism. But GCs are also known to regulate various brain functions, involved in human cognition (Cahill & McGaugh, 1996). Increased GC exposure in human
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beings at levels associated with stress has most often been found to decrease memory and learning function (see below). Evidence of these effects in adult human beings and animals has been reviewed by Hefflinger and Newcomer
(2001). As an aside, these authors pointed out that less is know about cortisol and memory in children and older people than in adolescents and adults. But Cahill and McGaugh (1996) have speculated that cortisol levels can, in some circumstances, enhance memory function. Buchanan and Lovallo (2001) attempted to test this idea and to extend findings with animals to human memory performance. Following administration of cortisol or placebo, college aged participants were exposed to pictures varying in emotional arousal. Incidental memory for the pictures was assessed one week later. Results showed that elevated cortisol levels during memory encoding enhanced the long-term recall performance of emotionally arousing pictures relative to neutral pictures. It is not clear why cortisol should selectively support memory for emotion provoking stimuli. But in general the results suggest that cortisol secretion can have beneficial cognitive effects in some circumstances. Note that Buchanan and Lovallo failed to control for state dependency, which once again prevents a clear interpretation of the role of stress (or cortisol) in encoding vs. retrieval processes.
Most of the recent literature with human subjects is not consistent with the results of Buchanan and Lovallo (2001), and more in line with the adverse effects of elevanted cortisol claimed by Hefflinger and Newcomer (2001). For example,
Kirschbaum, Wolf, May, Wippich, et al. (1996) reported two experiments on the association between cortisol levels and memory in healthy human adults. In the first study, subjects were exposed to the Trier Social Stress Test with a subsequent test of declarative memory performance. Results indicated a significant negative relationship between stress-induced cortisol levels and performance in the memory task. The second experiment investigated whether cortisol alone, independent of psychological stress, would also impair memory function. Male Ss received either
10 mg cortisol or a placebo orally. One hour later they were tested for procedural and declarative memory and spatial thinking. Subjects who received cortisol showed impaired performance in the explicit declarative memory and spatial thinking tasks although not in the implicit procedural memory task. Accordingly, their results suggest that, in healthy adults, elevated free cortisol levels may be associated with impaired explicit memory function, that is, functions that require conscious awareness and an important role for working memory, but not functions that operate automatically.
Wolf, Schommer, Hellhammer, McEwen, Kirchbaum, (2001)) reviewed epidemiological and experimental studies and found that elderly subjects are
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especially susceptible to memory impairing effects of elevated cortisol levels, postmenopausal women more so than elderly men. They noted further that, on the whole, little is known about gender differences in susceptibility to acute stress in young subjects. Therefore,Wolf at al (2001) conducted a study of healthy college students who learned a word list, with recall being tested after a brief distraction task. Some of their subjects learned the list after exposure to a psychosocial stressor, while the remaining subjects served as controls. Free cortisol was determined via saliva samples taken before and 10 mins after stress. Subjects exposed to the stressor, did not show impaired memory performance per se when compared to the control group. However the size of the cortisol increase in response to the stressor was negatively correlated with the memory performance within the stressed group (i.e., subjects showing a larger cortisol response recalled fewer words than subjects showing only a small cortisol increase). Additional analysis by Wolf et al. (2001) revealed that this correlation was high in men and nonexistent in women. The data suggest that gender might modulate the association between cortisol and memory after stress.
Newcomer, Selke, Melson, Hershey, Craft, Richards, and Alderson, (1999) reported an experiment in which participants were given 1 of 2 oral hydrocortisone doses or a placebo. Paragraph recall was used as a measure of verbal declarative memory. Results indicate that several days of exposure to cortisol at doses and plasma concentrations associated with physical and psychological stress in human beings decreases verbal declarative memory function in otherwise healthy human beings. A nother r elated r esult w as r eported b y Vedhara, H yde, Gilchrist,
Tytherleigh, and Plummer, (2000), who conducted an investigation to explore the relationship between acute changes in cortisol and memory and attention in the context of an acute naturalistic stressor, namely, examination stress in college students. Assessments of self-reported levels of stress, salivary cortisol, short term memory, selective and divided attention, and auditory verbal working memory were conducted during a non-exam and an exam period. The results revealed that the exam period was associated with an increase in perceived levels of stress, but also a significant reduction in levels of salivary cortisol, compared with the non-exam period. This reduction in cortisol was associated with enhanced short-term memory (as measured by the total number of words recalled in a free recall task), impaired attention and an impairment in the primacy effect (a hippocampal-specific index of short term memory), but no significant effects on auditory verbal working memory.
Further confusing the picture is a study reported by Lupien, Gillin, and
Hauger (1999) who measured the effects of various doses of hydrocortisone on
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performance in tasks assessing working and declarative memory function. During the infusion period, participants were given an item-recognition working memory task, a paired-associate declarative memory task, and a continuous performance task used to control possible concomitant effects of corticosteroids on vigilance.
The results revealed significant acute degrading effects of the highest dose of hydrocortisone on working memory function, without any significant effect on declarative memory function or arousal-vigilance performance. These results suggest that working memory is more sensitive than declarative memory to the acute elevations of corticosteroids, which could explain the detrimental effects of corticosteroids on acquisition and consolidation of information, sometimes reported in the literature (Cahill & McGaugh, 1996). Taken as a whole, the available data support the unsatisfactory conclusion that cortisol modulates cognitive processes, but in a highly selective manner
The results of Wolf et al., Vedhara et al, Newcomer et al., and Lupien et al. all appear to be inconsistent with Buchanan and Lovallo’s finding of cortisol support for retrospective memory of emotion-arousing stimuli. More data will be required to reconcile this discrepancy. Of course, one possible explanation is that various researchers induced or measured cortisol levels at different points on the
Yerkes-Dodson function. Thus, Buchanan and Lovallo’s data might to attributable to a relatively low cortisol level in their subjects, thereby facilitating performance on the upward rise of the Y-D function, while other researchers induced or measured higher levels of cortisol, beyond the optimum on the Y-D function.
More than anything else, this possibility demonstrates how slippery the issue is and how the Y-D principle can be used to explain almost any outcome. Further complicating the picture is the fact that none of these experiments took account of possible state dependency effects. Thus it remains unclear whether the effects of elevated cortisol levels, whether facilitative or adverse, are the same on encoding and retrieval processes in memory.
According to de Kloet, Oitzl, and Joëls (1999), some of the discrepancies reported in the memory literature as regards the role of corticosteroid hormones might be explained by appealing to the specific role of both mineralocorticoid and
GC receptors in the various stages of information processing. Corticosteroid effects on cognition can turn from adaptive into maladaptive when actions via the two corticosteroid-receptor types are imbalanced for a prolonged period of time. But before we should accept the de Kloet et al. claim, or any other possibility that relies on biological explanation, experiments with proper control and manipulation of cortisol levels and state dependencies in encoding and retrieval will need to be conducted and reported.
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Context and State Dependency involving Stress.
One of very few studies to take account of state and context dependency effects in memory was conducted by Thompson, Williams, L 'Esperance, and
Cornelius (2001). In the first of two experiments, experienced skydivers learned word lists prior to skydiving either in the air or on the ground and recalled them in the same context or in the other context. The second experiment was a replication of the first except that participants were shown a skydiving video in lieu of actual skydiving. Recall was poor in air-learning conditions with actual skydiving, whether learning took place in the air or on the ground. But when lists were learned on land, recall was higher in the matching context than in the mismatching context. In the skydiving video experiment, recall was higher in matching learnrecall contexts regardless of the situation in which learning occurred. It is proposed then that under extremely emotionally arousing circumstances, environmental and/or mood cues are unlikely to become encoded or linked to newly acquired information and thus cannot serve as cues to retrieval. Context and state dependency effects are real, but might be overridden when emotions are extreme.
Results can be applied to understanding variations in context-dependent memory in occupations in which the worker experiences considerable emotional stress while learning or recalling new information. But the main point is that these dependency effects must to be taken into account in all future experiments purporting to study stress and memory.
Other Considerations
False memories. Payne, Nadel, Allen, Thomas, and Jacobs (2002) demonstrated that stress can enhance a person’s susceptibility to false memories.
In a recall task, participants ' ability to distinguish words that were presented for study from critical lure words that were semantically related, but not presented for study, was selectively disrupted. This finding indicates that stress potentiates false memories. An argument was made by the authors that this effect is mediated through the impact of stress on the hippocampus and prefrontal cortex, but this interpretation is an extreme extrapolation from the data, which contained no measurements of brain activity.
Intrusive thoughts. Not only does stress affect and often limit memory, but also memories of stressful events can provide a basis for intrusive thoughts, resulting in persistent, protracted, lingering, or chronic stress – a kind of vicious circle (Baum, Cohen, & Hall, M, 1993). Intrusive thoughts have been identified as
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key elements in chronic or traumatic stress and the post-traumatic stress syndrome, but many questions remain about how they operate and what causes their persistence over time. Schooler, Dougall, and Baum (1999) considered these questions, examining the impact of having intrusive thoughts that are cued by stimuli in one 's environment as opposed to non-cued intrusions that seem to "come out of the blue." This research evaluated the extent to which distress accompanying intrusive thoughts shortly after a traumatic event predicts persistence of intrusions over time. Rescue workers who responded to the crash of Flight 427 were studied
4-8 weeks, and 6, 9, and 12 months after the disaster. Participants who reported crash-related thoughts that were not prompted by cues showed higher levels of distress than those reporting only cued thoughts or those reporting neither. The magnitude of distress that these non-cued thoughts caused in the first 2 months after the crash was important in predicting subsequent frequency of unwanted thoughts. Matthews (1996) has argued that intrusive thoughts and other “worries” occupy space in working memory, thus limiting performance in tasks that rely on working memory. But, at this time, no one has reported any solid evidence to support the detrimental effects of intrusive thoughts, whether cued or non-cued, on subsequent cognitive task performance.
A Memory Constriction Hypothesis
As noted earlier, one important distinction in contemporary memory research and theory applies to the temporal focus of information to be retrieved from memory and used. This distinction is based on a continuum from the remote past – retrospective long term memory – to the present or near present – short term memory and immediate or working memory – to the future – prospective memory.
The effects of important variables, including stress variables, might not be the same in all of these cases. Somewhat surprisingly, the data available on possible differences are surprisingly skimpy. Moreover, there are few systematic studies of stress on memory over a wide range of stress values. To our knowledge, there are no direct comparisons of retrospective, working, and prospective memory under stress. What evidence is available seems to suggest that stress typically causes the performer to focus on the here-and-now, with consequent degradation in retrospective and prospective memory. The results are consistent with a memory constriction or tunneling (Bernsten, 2002) hypothesis to the effect that the time span from which knowledge can easily be retrieved and used in a given context shrinks as stress level increases. Neglect of facts or procedures in long term memory, and failure to execute required behaviors at appointed future times might be a major reason for performance errors or failures in emergencies. Unfortunately,
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at the present time, empirical evidence to support this hypothesis is nonexistent.
The hypothesis could, however, serve as a framework for future research efforts.
Conclusions
A variety of stressful conditions affect a variety of memory measures, usually but not always in an adverse way. Mandler was one of the first cognitive psychologists to theorize about these effects, attributing them to cognitive resource limitations and to stress-produced noise in the cognitive system. People with high math anxiety have a reduced working memory capacity and, because working memory is required by many arithmetic and mathematical tasks, math anxious subjects perform more poorly on these tasks than low anxious subjects. There is conflicting evidence in the literature regarding memory for emotionally arousing stimuli. Many studies have reported that memory is better for either pleasant or unpleasant material than it is for emotionally neutral material. But there is some evidence that traumatic stimuli can inhibit memory for simultaneously presented neutral material.
There is extensive evidence that cortisol level is correlated with memory. But sometimes elevated cortisol levels have been shown to have a positive effect and sometimes a negative effect on memory. One possible explanation is that various researchers induced or measured cortisol levels at different points on the Yerkes-Dodson function. Further complicating the picture is the fact that few stress/memory experiments have taken account of possible state dependency effects. Thus it is unclear whether the effects of elevated cortisol levels, whether facilitative or adverse, are the same on encoding and retrieval processes in memory.
Not only does stress affect and often limit memory, but also memories of stressful events can provide a basis for intrusive thoughts, resulting in persistent, protracted, lingering, or chronic stress – a kind of vicious circle. To date, no one has reported on the possible detrimental effects of intrusive thoughts on cognitive task performance.
Environmental Conditions that Induce Stress
Time Pressure
One of the most obvious ways to put a performer under stress is to impose time limitations on the task or to give frequent “hurry up signals.” Intuitively, most people feel that they do not do their best work under time pressure, although there might be important individual differences in this regard. It is surprising therefore to discover that the literature contains very little evidence on the effects of time pressure on cognitive performance. Moreover, those studies that have been reported find rather obvious and uninteresting results.
The task used by Van Galen and van Huygevoort (2000) required subjects to make cursor movements to targets varying in width and distance. On the basis of
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the theory of van Ghemmert and Van Galen (1997), which has been described elsewhere, the authors tested the prediction that time pressure and dual task load would influence error rates and movement variability, together resulting in biomechanical adaptations of pressure on the cursor control. The latter is seen as a manifestation of a filtering strategy to cope with increased neuromotor noise levels. The results confirmed that, especially under time pressure, error rates and movement variability were enhanced, while cursor control pressure was higher in both conditions of stress.
Ashcraft (2002) has demonstrated that the performance decrement suffered by math anxious subjects on quantitative problem solving is in part attributable to a compromised working memory. In an extension of this idea, Kellogg, Hopko, and
Ashcraft (1999), following Matthews (1996), tested whether the limitation of working memory observed in anxious subjects might be the result of worry, i.e., that their consciousness is occupied to some extent by concern over the likelihood of poor performance. Time pressure could be a factor contributing to worry and thus to the poorer performance of anxious subjects. These researchers found, however, contrary to the worry hypothesis, that time pressure lowered performance of both anxious and non-anxious subjects equally. Thus the worry resource model was not supported by their data.
When response time deadlines are imposed in quantitative tasks, such as addition or multiplication, performers often adopt a strategy that is different from the one they would use in normal circumstances. Typically, these adopted strategies place less of a demand on working memory. For example, Campbell and
Austin (2002) showed that adult subjects shifted from a calculation-based or procedural strategy to a direct memory retrieval strategy to perform mental addition problems when they were put under time pressure. Performance suffered as a consequence of this shift, especially in more difficult problems
Entin and Serfaty (1990) reported an experiment to investigate the effects of time pressure on decision-making. Their paradigm involved a single decision maker whose job was to classify submarine sonar returns as coming from a friendly or enemy boat, on the basis of differences in average pump noise frequency between the two classes. After being given the value of the unknown submarine 's measured pump frequency, the subject either classified the submarine as friend or foe or, for a cost, asked for more information. This information was chosen to be either another raw measurement (probe) or the opinion of an automated consultant. Two distinct subject populations were used, civilian
(engineering firm employees and college students) and military. For both groups,
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performance under time pressure was significantly poorer than normal. The effects of time pressure are, then, what one would intuitively expect them to be. The researchers provided no speculation as to the underlying processes that might be engaged by time pressure and how they operated to affect performance.
Furthermore, because only two conditions were used, the experiment yields no evidence on the shape of the function between performance and time pressure.
Two person command and control teams were trained, in an experiment reported by Lehner, Seyed-Solorforough, O 'Connor, Sak, and Mullin (1997), to make decisions using a prescribed strategy following a set of simple decision procedures. The authors were interested in the impact of time stress on the decision-making performance of teams. The results supported the conclusion that prescribed decision procedures, which were somewhat counter-intuitive, would be more vulnerable to the effects of time stress than other more familiar and intuitive decision procedures. In addition, the results suggested that the subjects adapted inappropriately to time stress. As time stress increased, they began to use a decision processing strategy that was less effective than the strategy they were trained to use, reverting to procedures that were more familiar to them. While this study focuses on team performance, there is nothing in the data to suggest that same results would not be obtained with individuals working alone.
A study by Ozel (2001) provides greater insight into the effects that time pressure can have on fundamental cognitive processes. Ozel examined the manner in which stress, created by the threat of fire, affects how people process information provided to them about the correct escape route. Ozel reported that modest stress was beneficial to performance, but that extreme time pressure impeded performance by narrowing the range of environmental cues attended to or processed, an outcome predicted by Easterbrook (1959). In addition, the use of negative coping styles increased with time pressure.
Work Load and Overload
It is difficult, for reasons mentioned elsewhere in this review, to create extreme or prolonged conditions of stress in the laboratory. Laboratory studies generally focus on relatively weak acute stress. An example involves adding workload or secondary task requirements to a primary or focal task. Subjects often find these additions to be stressful at least at the outset and they can adversely affect primary task performance. Given some experience or practice, however, individuals can often find ways to accommodate to the greater demands of doing two things at once.
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Consider the work of Matthews, Sparkes, and Bygrave, (1996), who tested the hypothesis that driver stress is associated with performance impairment mainly because stress-prone drivers are vulnerable to overload of attentional resources. In other words, those who are susceptible to the effects of stress suffer from limitations on attentional resources and are more distractible by irrelevant nondriving events. Young subjects performed a simulated drive concurrently with a grammatical reasoning task, presented either visually or auditorily. In this experiment, the patterns of dual-task interference predicted by attentional resource theory were actually not found, although some interference was apparent with the auditory reasoning task. Measures of vulnerability to driver stress and intrusive cognitions were related to impaired lateral control of the vehicle mainly when task demands were relatively low, contrary to the overload hypothesis. These data indicate that performance in this task paradigm is characterized by adaptive mobilization of effort to meet changing task demands. Stressed drivers adapted to high levels of demand fairly efficiently. The levels of stress involved here obviously fall within the range that can be compensated for by strain or mobilization. But, in contrast, Metzger and Parasuraman, (2001) found that, at higher levels of overload, created by a secondary task during driving in high traffic density and assessed by HR and self-report measures, performance does gradually but significantly decline. Parallel results were reported by Zeier (1994) for air traffic controllers.
With practice, people often find ways to incorporate secondary task requirements into the strategy they use to perform the primary task. Healy,
Wohldmann, Parker, and Bourne (submitted), for example, recently reported evidence of this phenomenon in a series of experiments on time estimation. Two groups of subjects were trained on a time estimation task under stress created by various secondary tasks. One secondary task was relatively easy, requiring the repeated articulation of a given letter of the alphabet. The other secondary task was quite difficult, requiring recitation of the alphabet backward by three 's starting with a given letter. Performance in these conditions was compared to that of a third, control group, trained without the stress of a secondary task. Training led to improvements in performance in all three conditions but training with the difficult secondary task degraded, or strained, performance considerably relative to the other two conditions. Importantly, removing the secondary tasks after training in a transfer task actually impaired performance for those subjects trained with either secondary task relative to the control. In fact, performance was worse after training for subjects in the difficult secondary task condition than it was at the beginning of training for subjects in the control condition. This is a surprising and
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unique finding with crucial implications both for training and for understanding workload and stress effects. It is consistent with the procedural reinstatement principle proposed by Healy and Bourne (1995) if it is assumed that the procedures used by subjects to estimate time somehow accommodated the requirements of the specific secondary task. The idea is that when the secondary task is removed in the transfer session, new procedures are required to perform the primary task alone, leading to an initial performance decrement.
The results of this study raise an interesting empirical question about training to contend with stressors. Training may be specific to the particular stressor or stressors that are present during practice. The procedural reinstatement principle implies that training with one stressor will not necessarily generalize to test conditions (i.e., to retention, transfer, or retraining) under other stressors. For example, training under the stress of time pressure to respond may enhance subsequent performance under another type of time pressure, but may not adequately prepare individuals for subsequent performance under conditions of fatigue or work overload. In fact, training under time pressure may put a person at a disadvantage when tested under different adverse conditions. The results of
Matthews et al. (1996), who studied driving under various stress conditions are consistent, although not definitive, with respect to this expectation. Training under two or more adverse conditions may support wider generalization at test even when the adverse conditions at training do not match those at testing, in agreement with a variability of practice hypothesis of Schmidt and Bjork (1992). What actually happens, of course, is an important empirical question that needs to be addressed at some point in this project.
Information overload threatens our limited cognitive capacity and can quickly degrade performance in many daily tasks (for the classic argument, see
Miller, 1956). Fitts (1966), for example, demonstrated that an overload condition created by time pressures significantly increased error rates in a complex reaction time task. Under circumstances of high information load, artificial memory aids can be especially beneficial to performance. In most experiments that have examined time pressure, the decline in performance is gradual rather than catastrophic, as would be case if cognition was completely overwhelmed. As an example of how this works, consider a recent series of experiments by Burrows
(2002) that examined how workload variables such as amount of information, speed of information presentation, and secondary task requirements, interact to create a condition of overload and how they influence recognition memory.
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Burrows (2002) measured the recognition of previously presented words, with the length of the memory list increasing with each presentation. Gradual declines in recognition performance were observed over trials (and with expanding lists). It is important to note that performance degradation was gradual, rather than abrupt. Subjects were able to adjust to conditions of overload by maintaining in memory some significant portion of the materials to be retained. When rate of information presentation was increased, performance was adversely affected, but the slope of degradation function associated with increasing the size of the memory list was not changed. That is, recognition memory decreased gradually as the size of the list increased and as the rate of presentation increased, but these variables did not interact. In one final experiment, Burrows required his subjects to perform a second task simultaneous with recognition memory. Several new items were added to the memory list on each successive trial, and, in addition, subjects were instructed to forget or eliminate a small subset of earlier items. Thus, each memory trial required not only adding new items but also deleting others and a reorganization of the remaining memory list. The requirement to delete and reorganize in memory degraded overall performance. The effects were entirely attributable to mishandling the deleted items. That is, performance on retained and added items was the same in the standard learning condition. But subjects were completely incapable of retaining the current status of deleted items, sometimes recalling them as part of the list and sometimes not.
Burrows’s studies suggest two major conclusions regarding the workload placed on memory. First, expanding the length of a list to be remembered causes a gradual (non-catastrophic) decrease in performance. Second, the requirement to reorganize an expanding list does result in an abrupt decline in performance mainly attributable to a complete forgetting of the status of deleted items. The practical implications of these results are likewise two-fold. First, when new information is periodically introduced into a task, modest memory aids, such as temporary reminders of the new items, will offset the increased memory load. However, when reorganization and up-dating are required, aids that keep track especially of the once-but-no-longer relevant items are especially helpful. Memory up-dating of the current state of a complex systems is uniquely vulnerable to the effects of information load and possible other stressors.
Adding a secondary task to a primary task can create an information overload situation, but information overload can also occur within the context of a single, primary task. Suppose individuals are required to learn rapidly a large quantity of new facts in some specific domain, which is commonly the case with the introduction of new complex systems into the workplace. The effects of this kind
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of information overload on learning and subsequent performance are not well understood by cognitive psychologists but should generally be detrimental. If the overload is severe, then it will impose a form of cognitive stress (Humara, 2002), and it is important for the operator to develop coping strategies to deal with this stress. Van Overschelde and Healy (2001) recently reported a series of experiments to investigate how the level of knowledge participants have about a domain affects their ability to cope with a large number of new, non-domain relevant facts about persons within their domain of expertise. To create a situation of information overload, Van Overschelde and Healy required subjects to learn 12 new facts about each of 12 persons (i.e., 144 new facts in total). They found that subjects who had a high degree of knowledge in a particular domain (e.g., about baseball or movies) were better able to learn new facts about famous persons from that domain than to learn new facts about persons from a domain of which they had a low degree of knowledge, even though the facts themselves were not relevant to either domain.
In a second experiment, Van Overschelde and Healy created a novel knowledge base, by having subjects learn five facts about each of six previously unknown persons, and one fact about each of six other persons. Two days subsequent to this pre-training experience, participants learned 12 new facts about each of the 12 persons. Participants were significantly better at learning new facts about persons for whom they had learned five facts initially than about persons for whom they had learned only one fact initially.
As noted earlier, these studies suggest that one mechanism for coping with information overload and reducing the stress overload engenders is to provide connections between the new facts to be learned and an existing knowledge base.
The general principle is that the acquisition and retention of new, factual information is facilitated whenever that new information can be linked to an existing knowledge base. The mechanism underlying this strategic-use-ofknowledge principle is based on the provision of a retrieval strategy supported by factual information that already exists in long-term memory. Future experiments might profitably focus on the provision of different retrieval strategies to validate their effectiveness and to document which strategies work best.
Fatigue and Sleep Deprivation
Laboratory studies. When a people work at a continuous, demanding task, such as the operation of a complex electronic system, their performance might be affected by at least two opposing processes. First, performance might improve, becoming more accurate and faster as operators master the skills required of the task. Second, performance might deteriorate as individuals suffer the effects of
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fatigue over long periods of uninterrupted work. The effects of fatigue are likely to be transient, dissipating over periods of rest interpolated between periods of work.
The effects of skill acquisition, however, should be relatively permanent, persisting long after fatigue has worn off. Testing this differential effect of prolonged work has yet to be adequately accomplished and is likely to be the focus of future research in the general domain of stress (caused by fatigue) and cognition.
Healy, Bourne, and colleagues (Buck-Gengler & Healy, 2001; see also
Fendrich, Gesi, Healy, & Bourne, 1995) have recently reported several experiments addressing certain aspects of fatigue in a repetitive data entry task. In one experiment, there were two sessions separated by a one-week delay. In each session, subjects typed strings of 4-digit numbers viewed as numerals displayed on a screen. A short break halfway through the first (training) session allowed subjects some degree of recovery from fatigue. These researchers found that, during training in the first session, accuracy of performance decreased from the first to the second half of the session and across blocks within each session half.
This finding documents the successful induction of fatigue during training.
Nevertheless, these researchers also found that, during training, response time decreased from the first to the second half of the session and across blocks within each session half, suggesting that practice and fatigue combined to lead to a speedaccuracy tradeoff.
The observed speed-accuracy trade-off illustrates two important general caveats concerning the effects of stressors, such as fatigue, on performance. The first is that stress effects may be different for different measures or indices of performance (in this case, speed and accuracy). The second is that the effects of stressors may not always be harmful. This latter conclusion, of course, follows from the Y-D law, which specifies an optimal level of arousal (resulting from stress) for any person and any task. But what is demonstrated in these experiments is slightly different; here one stressor actually facilitates response times and simultaneously inhibits accuracy. The generality of this observation needs to be checked in other tasks and training conditions. For example, in a more cognitively demanding task than data entry, such as mental calculation (e.g., Rickard, Healy, &
Bourne, 1994), fatigue effects might be less severe or possibly non-differential on performance measures.
The observation that fatigue or other stressors might not matter or might even have a beneficial effect on some measures of performance seems inconsistent with common sense and is certainly contrary to corporate wisdom. Every manager knows that if you keep people up for 48 hrs, they will not handle the workload as
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well as they can when they are fresh. To interpret these results accurately, we need to keep in mind that the level of fatigue induced in laboratory studies might simply be too minimal to cause serious performance degradation. It is also important to recognize that most cognitive studies performed in the laboratory have addressed acute fatigue developed over relatively short work periods. Principles uncovered in these conditions are unlikely to apply to more chronic or stronger fatigue states.
Therefore, in the future, experimenters should try to find ways to expand their research on fatigue both to more intense and to chronic conditions. This expansion might be accomplished, for example, by the use of sleep deprivation or imposed deviations from normal circadian rhythms.
The results of Soetens, Hueting, and Wauters (1992) show that the effects of fatigue might vary with task difficulty. Using a numerosity judgement task, these researchers found that, under fatigue, errors were greater for larger displays (7+ dots in the visual field to be judged). No difference between fatigued and nonfatigued subjects were observed at smaller displays. Small numbers can be estimated accurately by an automatic process known as subitizing. Larger numbers require attention and mental work, including counting. Fatigue reduces or eliminates controlled processing required by larger numbers, leading to more errors. Their conclusion was that fatigued subjects tend to avoid or fail at complex decisions. Steyvers and Gaillard (1993) examined the possibility that knowledge of results (KR) and reward might compensate for the negative effects of sleep deprivation in a choice-reaction task. They found that the effect of signal degradation on performance was aggravated by sleep loss and time-on-task, confirming the observation of Soetens, et al. (1992). They also reported that KR improved performance, especially when signals were degraded. Reward counteracted to some extent the effects of time-on-task owing to lack of sleep.
Consistent with the finding of Buck-Gengler and Healy (2001), performance also improved as the result of a brief task interruption after 30 min. of work.
EEG measures are sensitive to abnormal conditions such as fatigue and sleep deprivation. This fact suggests the possibility that neuro-physiological measures, such as the EEG, might be used to differentiate stress states of the organism from normal or other abnormal states. Gevins and Smith (1999) reported that both alcohol intoxication and fatigue reduced the accuracy of performance in a working memory task and that these effects were associated with changes in spectral characteristics of the EEG. Human observers and digital networks trained
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on human data could discriminate fatigue and alcohol states in the EEG from normal alert states with accuracy well over 90%.
Natural tasks. There has been a fair amount of research on fatigue in more natural situations. For example, Matthews and Desmond (2002) induced fatigue in a simulated driving task by requiring subjects to perform a demanding secondary task while driving. Their induction procedure produced subjective feelings of fatigue and stress and of heightened workload. With respect to driving performance, fatigue induction increased errors of heading, steering, and reduced perceptual sensitivity in the secondary task. These researchers also report, however that added motivation partially overcame these adverse effects of stress.
They attributed the primary effect of a secondary task (1) to the division of attentional resources in the dual task case and (2) to a failure to adjust effort to level of task demands.
Schellekens, Sijtsma, Vegter, and Meijman (2000) demonstrated some persistent effects of demanding day-long office work on cognition. These researchers administered a memory search task before, during, immediately after, and 2 hrs. after either an easy day of work or a demanding day of work.
Performance measures on the search task were RT and accuracy. Effort on task was measured physiologically by HR. Accuracy decreased slightly on the immediate test after a difficult day, relative to tests administered before and during the work-day. Also, subjects invested significantly less effort in the memory task after a difficult day relative to an easy day. In a delayed test, a speed/accuracy trade off was observed. After a demanding day, RTs increased and accuracy decreased in the delayed measure, results similar to those reported by BuckGengler and Healy (2001) obtained in a laboratory setting. Apparently, under some circumstances, fatigue has latent effects that only show up after sufficient passage of time. Further, recovery from fatigue requires rest and time away from task.
Many occupations require not only extended work periods, exceeding the normal 8 hrs, but also are physically demanding and provide few if any breaks.
Operators of public transportation equipment are a good example of this kind of work environment. Raggatt and Morrissey (1997) measured stress and arousal in
10 long-distance bus drivers during 12-hr driving shifts and at matched times on non-driving rest days. The objectives of the study were (1) to compare the stress measures collected on the road, which included HR, BP, catecholamines, cortisol, state anxiety, and self-ratings of stress and arousal, with matched rest-day baseline measures, and (2) to investigate the pattern of arousal over the course of shifts. It was expected that certain psycho-physiological changes would take place during
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long-distance driving and these changes would be associated with driving fatigue.
Cardiovascular and catecholamine data were elevated across the entire work-day, compared with rest days. Self-reported stress and state anxiety were elevated only at the pre-shift measure, and these elevations were interpreted to be the result of anticipatory anxiety and additional work demands at the beginning of the shift.
Decelerating activation from the 9th-12th hrs of driving were reflected in slower
HR and lower subjective arousal ratings. Apparently drivers experience a release of tension when they anticipate the end of the shift and therefore deactivation is a signal or precursor to the onset of fatigue. Measures of driving performance remained relatively stable over a 12 hr shift. Experienced drivers seem to have acquired coping strategies that allow them to maintain stable performance levels when work sessions are of known duration and do not exceed 12 hrs. As in the case of long-term isolation, cognitive effects of stress appear to be ameliorated by knowledge that the stressful situation, although long, is time limited
But Raggatt amd Morrissey (1997) also found that performance falls when shift length is uncertain or exceeds the normal 12 hr limit. Performance degrades before changes are evident in physiological measures. This result is consistent with the conclusion of Hancock and Vasmatzidis (1998) that continued work requirements after performance efficiency begins to fail, but before current physiological limits are reached, is inappropriate for both the safety and the productivity of the individual worker, their colleagues, and the systems within which they operate. Behavioral performance assessment should therefore supercede physiological assessment as the primary exposure criterion, although physiological measures still provide important supplementary information.
Even without a work requirement, long periods of sleep deprivation can have serious cognitive consequences. Baranski, Gil, McLellan, Moroz, Buguet, and Radomski (2002), for example, showed that 40 hrs of sleep deprivation severely affected cognitive performance on seven cognitive tasks -- serial reaction time, logical reasoning, visual comparison, mental addition, vigilance, and multitasking -- to essentially the same degree on all tasks.
Samel, Wegmann, Vejvoda, Drescher, Gundel, Manzey, and Wensel (1997) investigated two-person crew extended range operations over 2 consecutive night flights with a short layover. Pre-, in-, and post-flight measurements of sleep, task load, fatigue, and stress using EEG, ECG, motor activity and subjective ratings were collected for 11 rotations (22 flights) from 22 male pilots. Average flight times were 9 hrs with an average daytime layover of 13 hrs 30 mins. Results showed that sleep during layover was shortened by an average of 2 hrs relative to
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normal. Fatigue was more pronounced during the return flight and several pilots scored their fatigue at a critical level. Motor activity, brain wave activity, and HR indicated drowsiness and a low state of vigilance and alertness during both night flights, but these effects were more pronounced during the return flight. A survey of military pilots reveals that they suffer chronically from sleep deprivation
(Caldwell & Gilreath, 2002). Insufficient sleep, combined with rotating schedules and other work demands, no doubt contributes to the perception that fatigue is a widespread problem in the aviation community. These results indicate the importance of continuing to employ fatigue-reduction strategies in training and operational environments.
To what degree can fatigue effects be offset by periods of rest? Neri,
Oyung, Colletti, Mallis, Tam, and Dinges (2002) arranged for 14 2-man crews to participate in a 6 hr, uneventful, nighttime flight in a Boeing 747-400 flight simulator. Crew members in the treatment group received 5 short breaks spaced hourly during cruise; the 14 crew members in the control group received 1 longer break in the middle of cruise. The treatment group reported significantly greater subjective alertness for up to 25 min. post-break, with strongest effects near the time of the circadian trough. There was no evidence of objective vigilance performance improvement at 15-25 min. post-break, with expected performance deterioration occurring due to elevated sleep drive and circadian time. In situations that require sustained attention over a prolonged period of time, e.g., during a long overnight flight, brief and regularly spaced breaks improve alertness and performance. What about stimulating drugs? Can they offset the effects of fatigue, without causing adverse consequences of their own? Caldwell (2001; see also
Caldwell & Gilreath, 2002) reported a quasi-experimental comparison of modafinil
(Provigil (R)) and dextroamphetamine (Dexedrine (R)) on the performance of sleep deprived pilots. Subjects were given either dextroamphetamine or modafinil and then undertook a flight simulation. Results indicate that there were no differences between the 2 stimulants. However, in the majority of cases, it was clear that performance, subjective mood ratings, and physiological indices of alertness were substantially better under both drugs than under placebo. Thus, with the exception that modafinil produced more spontaneous reports of side effects than dextroamphetamine, the overall results indicated equivalent efficacy with the
2 compounds.
There are at least two studies which have examined the interaction of sleep deprivation with other stressor variables. von Restorff, Kleinhanss, Schaad, and
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Gorges (1989) investigated human tolerance limits for sustained performance on several simple psychological tests. Subjects performed continuously for 72 hr, with only 1 hr of sleep permitted after 32, 48 and 60 hr. The present experiment examined whether such sustained performance might be additionally influenced by mild hypoxia together with correspondingly increased carbon dioxide levels (stale air). Performance showed the expected decrease with increasing duration of sleep loss. However, findings show no clear differences in performance between the control and the hypoxia groups. There were, however, more pronounced decreases over time in both group in the more complex memory tasks as compared to simple reaction time and vigilance tasks.
Larsson (1989) looked at the interaction of sleep deprivation and the stress created by a noisy work environment. He measured the performance of Swedish military personnel on an artillery simulator under calm conditions, noisy conditions, and noisy conditions with 27 hrs sleep deprivation. Under all conditions, subjects who appraised the task as a challenge demonstrated positive coping and better performance, relative to those who appraised the situation as a threat. Performance degraded and negative coping increased with increasing sleep deprivation. Noise
Noise or atonal sound is everywhere in the modern world. People normally do well in adapting to these ambient and sometimes disagreeable sounds. But there are circumstances in which noise can be stressful enough to produce some adverse changes in human behavior. Early on, Hockey (1979) reviewed the psychological literature on noise-induced stress, concluding that there were five primary effects. First, stressful noise activates the performer often to a level that exceeds optimal for the task at hand, resulting in an increase in the rate of work but also an increase in errors. Second, stressful noise changes the performer’s policy for allocating attentional capacity, resulting in an apparent reduction in short-term or working memory. Third, attentional selectivity -- that is, limiting the attentional field, bringing relevant stimuli into sharper focus, focusing on the here and now, reducing memory search, relying on automatic as opposed to deliberate functions - is increased. Fourth, there is an increase in response selectivity. Finally, stressful noise reduces the performers confidence in his/her ability to do the task at hand.
These effects were observed primarily in studies using laboratory induced stress and laboratory tasks.
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Later, Kjellberg (1990) reviewed the psychological literature on the effects of noise in the work environment, emphasizing moderate-intensity noise (e.g., computers, printers, and ventilation systems). He found reports of significant distraction, and sleep disturbance in individuals who worked under constant noise conditions. He also found evidence of noise effects on reaction time (RT), vigilance, and verbal comprehension tasks. But, in many respects, the existing research presented a rather inconsistent picture of noise effects in natural work environments. Kjellberg (1990) recommended that, because of the potential seriousness of the nonauditory, cognitive effects of noise, more attention needs to be given to these effects in the occupational setting and in the research laboratory.
Little has changed in the last 10 years to modify that recommendation.
Larsson (1989) reported that performance by Swedish military personnel on an artillery simulator, a task requiring target identification, target tracking, decision making, and perceptual-motor co-ordination, degraded significantly in noisy conditions relative to calm and quiet conditions.
Kjellberg, Landstroem, Tesarz, et al. (1996) followed up a review of the noise literature (Kjellberg, 1990) with an examination of some of the factors that influence subjective responses to noise in 439 persons working in offices, laboratories, or industrial settings. Information about the workers’ subjective assessment of their working environment was collected by questionnaires. An annoyance index and a distraction index were formed on the basis of a factor analysis of questionnaire data. Annoyance was found mainly to be related to sound level, self-rated "necessity" of the noise, hearing status, and gender. Distraction was most strongly related to degree of self-control of the noise and noise predictability. The most critical noise sources for the annoyance response were other machines than those used by oneself, whereas telephone signals and conversations had the largest effect on distraction. Despite the annoyance and distraction effects of workplace noise, no significant influence on quality or quantity of work performance was detected. A moderate level of workplace noise might be stressful, but its potentially degrading effect on performance appears to be counteracted by extra effort in most circumstances.
In a related study, Gomes, Martinho Pimenta, and Castelo Branco (1999) investigated the effects of prolonged workplace exposure to large pressure amplitude (-90 dB SPL) and low frequency (
References: Complex operations can be performed successfully in Space by human beings, but more slowly than doing the same tasks on Earth (Fowler, Comfort & Bock, 2000; Watt, 1997)), Fowler, et al. (2000) and Manzey (2000) propose two hypotheses to account for this performance degradation—(1) the direct effects of microgravity on the central of human performance in Space, as suggested by the results of Watt (1997) among others, cognitive psychology can help solve the problem (2002) describes how 20 years of experience working in the Pentagon convinced him of the need for a greater understanding of human behavior and of human-machine interactions to improve military operations. Wastell and Newman (1996) have argued that a well-designed military system should realize the twin aims of enhancing human the military, which are especially concerned about performance of people in extraordinary conditions (see, eg., Dearnaley & Warr, 1979). clearly a distinct advantage to anyone caught in an emergency. Neufield (1999) has recently offered a promising formalism, based on nonlinear dynamics, that helps us studies of health and performance changes in chronically stressful circumstances. For example, Sauer, Juergen, Hockey, and Wastell (1999) reported a study of three Russian
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Subliminal perception is believed to be effected by its based finding of mind control, weather it’s one person or group of people. Mind control can be used on a group of people without their awareness. The perception of this idea is to get people to do things that would not normally do. For instance, during the 1950s there was a message that says Drink Coca-Cola which attack many people into trying this product or making them thirsty for a cold Coca Cola. This ad was used enter a person mind while making them thirsty for the item, because the company wants to sell their product (Pratkanis, 1992).…
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