Investigating the ‘Belief Bias’ Effect in Human Reasoning

Topics: Logic, Reasoning, Syllogism Pages: 9 (2942 words) Published: August 27, 2008
Investigating the ‘Belief Bias’ Effect in Human Reasoning Abstract
In this report an experiment was conducted to investigate the belief bias effect in human reason, the weighting attached to logic and belief in syllogistic reasoning. Belief biases were observed despite controls for conversion of premises. Belief bias was shown to be more marked in the invalid than the valid syllogisms. This consistent interaction between belief and logic was also noted. However, participants were intermediate in there response to syllogisms that were valid but had unbelievable conclusions. For 8 syllogisms presented, responses were collected as to whether the conclusion followed logically form the premises or not and a 2-factor ANOVA was performed in order to find the main effects and interaction present between the variables (believability & logicality) A conflict between logic and belief was identified and explored in terms of Evan Dual Process theory, which supposes 2 cognitive systems for human inference, the unconscious, autonomous system 1, and the uniquely human system 2, which requires slow conscious effort, enabling abstract thought and reasoning based on memory and prior beliefs. Introduction

Cognitive psychologists have long debated the notion of rationality in human inference. This debate has been split by irrational processes in the study of inductive and deductive inference (Nisbett & Ross, 1980) and the more dominant position of the rationalist interpretation of inferential behaviour (Revlin & Mayer, 1978). In the broader history of psychology, earlier than the mid 1960’s, there was a general assumption that we were quite logical in our decision making processes, such as in the case of deductive reasoning, whether of the ‘philosophers’ variety (Henle, 1962) or of an alternative ‘natural’ type (Braine, 1978), indicating that intelligence could be a predictor of logicality. However this view was to be challenged with much research in arising from the late 60’s/early 70’s, which focused on thinking and reasoning, and the obvious biases that we come to when making decisions.

Rationality is defined as ‘the possession of reason’ (, making it an interesting topic, underpinning the field of cognitive psychology, ‘the mental processes of perception, memory, judgement and reasoning’ ( As a main interest in this field is finding reasons in one’s actions, it makes sense to investigate the fundamentals which influence human reasoning, and thus there thoughts, feelings and actions. This study will investigate the effect of ‘belief bias’ in human reasoning, how much our pre-existing beliefs interfere with the way one comes to a decision, examining the conflict that arises between logic and reasoning in human inference. Tversky & Khaneman were key figures in the discovery of systematic human cognitive bias, in there work which explored heuristics in human reasoning. In psychology, heuristics are simple, efficient rules, hard-coded by evolutionary processes or learned, which have been proposed to explain how people make decisions, come to judgments, and solve problems, typically when facing complex problems or incomplete information. In this way the brain can be thought of a like a big computer and these rules work well under most circumstances, but in certain cases lead to systematic cognitive biases. Much of the work of discovering heuristics in human decision-makers was ignited by Tversky & Kahneman, asking ‘if the brain is just like a big computer, then why do seemingly intelligent people do stupid things? A rational employed in this study exploring the interaction of logic and belief. An early example in the study by Tversky & Kahneman exploring heuristics and biases in human cognition focus on how (representative) heuristics can be used to make judgments that are in principle accurate, even though no more (mathematically) likely. In there classic study, the ‘Linda the bank teller’ question,...

References: Braine, M. D. S. On the relation between natural logic of reasoning and standard logic. Psychological Review, 1978, (85) 1-21
Capon, A
Evans, J. St. B. T. & Barston, J. L. & Pollard, P. On the Conflict between Logic and Belief in Syllogistic Reasoning. Memory & Cognition. 1983, 11 (3), 295-306
Henle, M
Nisbett, R. E., & Ross, L. Human Inference; strategies and short-comings of social judgement. Englewood Cliffs, N.J: Prentice Hall, 1980
Revlin, R
Stanovich, K. E & West, R.F. Individual differences in reasoning: Implications for the rationality debate. Behavioural Brain Science, 2000, (23), 645-726
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