reaction times

Topics: Spinal cord, Reaction time, Neuron Pages: 6 (1266 words) Published: November 8, 2013
Biology 104

Reaction Times
Objectives:
1. Formulate and test hypotheses regarding reaction times.
Introduction:
Reaction time is a measure of how quickly an organism can respond to a particular stimulus. Reaction time has been widely studied, as its practical implications may be of great consequence, e.g. a slower than normal reaction time while driving can have grave results. Many factors have been shown to affect reaction times, including age, gender, physical fitness, fatigue, distraction, alcohol, personality type, and whether the stimulus is auditory or visual. The model for information flow within an organism can be represented in this way: Stimulus

Receptor

Integrator

Effector

Response

More specifically, in vertebrates, information flow can be represented in this way: Stimulus

Sensory Neuron

Spinal Cord or Brain

Motor Neuron

Response

Sensory neurons convert a stimulus into an electro-chemical signal, which flows the length of the sensory neuron(s), then through a neuron or neurons of the central nervous system, and then through the length of the motor neuron(s). Generally, motor neurons will cause a muscle to contract or a gland to secrete a substance. Reactions that involve only the receptor, the spinal cord, and the effector, are faster than those which involve processing in the brain. Reactions which only travel to, through, and from the spinal cord are often called spinal reflexes or cordmediated reflexes; withdrawing one’s hand from a hot stove is an example of such a reflex. In ‘simple reaction time’ experiments, there is only one stimulus and one response. Catching a dropped stick, or hitting a button when a light changes are examples. In ‘recognition reaction time’ experiments, there are symbols to respond to and symbols to be ignored. There is still only one correct stimulus and one response. An example would be catching a dropped stick with a word cue, while having to ignore other spoken words which are not cues.

In ‘choice reaction time’ experiments, there are multiple stimuli and multiple responses. The reaction must correspond to the correct stimulus. Typing a letter which matches a printed letter prompt is an example of this type of experiment.

Methods:
There are many methods to test reaction times; several tests are discussed here. Three involve catching a dropped ruler; the other is computer based and involves moving and clicking a mouse in response to a particular stimulus. You will design an experiment using one of the methods or comparing two of the methods.

Ruler Catching Methods: One way we can test reaction time in lab is by measuring the time it takes to catch a ruler dropped by an accomplice.
Method 1 -- Simple Reaction Time
1. Subject should hold out the chosen hand and extend the thumb and index finger so they are 8 cm apart.
2. Accomplice hold a metric ruler with its end exactly even with the subject’s extended thumb and index finger. The ruler should be vertical with lowest numbers near the subject’s hand. 3. The ruler is dropped, and the subject grasps it between the thumb and index finger. 5. Record the number at the subject’s fingertips, i.e. distance the ruler fell through the subject’s fingers.

6. Calculate the time it took for the subject to react and catch the falling ruler. The time (t) it took for the ruler to fall can be calculated from the distance it fell. Distance (d) fallen can be converted to time (t) passed with the following formula: 2 2

d (in cm) = (1/2)(980 cm/sec )t
2

2

t = d/(490 cm/sec )
2

t = √d/(490 cm/sec )
[980 cm/sec2 is the acceleration of a falling mass on Earth. Since we know how fast an object falls, we can figure out how long it took to fall a measured distance.] Methods 2: Reaction Times with a Word Cue: This method will once again calculate reaction time by calculating the time it takes to catch a dropped ruler, but in this method a final word cue is given, as well, after other words are spoken...

Bibliography: Kosinski, Robert J. 2005. A Literature Review of Reaction Time. Accessed March 17, 2005.
Marieb, Elaine N., Exercise 22 Human Reflex Physiology, Activity 9: Testing Reaction Time for
Basic and Acquired Reflexes, pp. 232-233, Human Anatomy and Physiology Laboratory Manual
(Cat Version), 2003,7th Ed.- Update, Benjamin Cummings, San Francisco, California.
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