Just for the fun of it, I thought I would post a paper that I had to write for my comparative animal physiology lab. Believe it or not, I'll write one of these every week for the rest of the semester!
Auditory & Visual Reflexes
Introduction
A reflex is a rapid response or movement to stimuli. The reflex arc, first described by Marshall Hall (1790-1857), is the pathway in which a sensory receptor is stimulated and signals pass from it along a sensory neuron to the spinal cord. Integrated in the central nervous system, the message then travels along a motor neuron to the effector organs causing them to respond. An example of this pathway is sneezing. A sneeze is triggered by foreign particle trapped in your nasal passage that agitates the surrounding sensory receptors. The message travels to the CNS and then back to effector organs causing you to exhale forcefully to remove the foreign particle. Other examples include salivation in response to the aroma of your favorite food; nausea to a nasty odor; blinking in response to an insect flying towards your eye. Since the neural signals are not sent directly to the brain, the simple reflex arc occurs very quickly without you even “knowing it”. A simple reflex arc includes only one stimulus and one response. Responses to auditory cues are faster than responses to visual cues. In this experiment we measured the reaction times of visual and auditory stimuli observing reaction to sound is faster than reaction to light. This is because an auditory stimulus only takes 8-10 msec to reach the brain (Kemp et al., 1973), but a visual stimulus takes 20-40 msec (Marshall et al., 1943). A visual reflex is more complicated and integrated, thus taking longer to be processed and understood by the brain.
Materials & Methods
Four exercises were conducted to measure the reaction time to particular auditory and visual stimuli. Equipment used included PC Computer, IWX/214 data acquisition unit, USB cable, IWX/214 Power supply and EM-100 Event marker. In all exercises, two subjects were instructed to sit in a chair, face or turn away from the computer screen (depending on the exercise) and position a hand on the keyboard that enabled the subject to push the enter key quickly in response to a visual or auditory stimuli. The subjects were not allowed to see the event marker which generated the visual signal on the computer screen. In each exercise 10 trials were performed.
Exercise 1 (Visual): The purpose was to measure the reaction time to a random visual cue. The subject was instructed to closely watch the right side of the computer screen for a green signal and upon seeing the signal push the enter key. Subjects did not see or hear the event marker in this exercise.
Exercise 2 (Auditory): The purpose was to measure the reaction time to a random auditory cue. The subject listened for the click sound of the event marker and pushed the enter key immediately upon hearing the click.
Exercise 3 (Prompted Auditory): The purpose was to measure the reaction time to an auditory cue delivered immediately after a verbal cue. Directly before the auditory cue was given the subject was prompted with the word “ready” upon which the subject pressed the enter key.
Exercise 4 (Predictable Auditory): The purpose was to measure the reaction time to auditory cues delivered at predictable intervals. The subject listened for the click sound of the event marker at approximately every five seconds and pressed the enter key as soon as possible.
Following each exercise, the delay in each of the 10 trials from the beginning of the green visual signal made with the event marker to the mark made by the subject’s response was measured. The shortest and longest times for each exercise and the 8 remaining times were averaged.
Results
Prompted auditory had the fastest reaction time then, predictable auditory, auditory and finally visual with the slowest reaction time. The table below summarizes the mean reaction times to each cue and the mean reaction time of both subjects for a particular cue.
Table 1: Mean Reaction Times for Different Cues.
Cue
Mean Reaction Time of Subject 1 (s)
Mean Reaction time of Subject 2 (s)
Mean Reaction time of all Subjects (s)
Visual
0.47
0.38
0.42
Auditory
0.28
0.36
0.32
Prompted Auditory
0.15
0.26
0.20
Predictable Auditory
0.27
0.22
0.24
The subject’s mean reaction times are comparable to each other in that they differ in a tenth of a second. We further observe that both subject’s mean reaction time to visual cues is slower compared to their mean reaction time to auditory cues. Subject 2’s fastest reaction time was during the predictable auditory cue whereas subject 1’s fastest reaction time was to the prompted auditory. Interestingly, subject 2 is male and subject 1 is female.
Discussion
The results imply that human brain processes auditory sound waves faster than light waves and reaction time increases speed when the first auditory cue is given to signal the second auditory cue or when cues occurs in a predictable manner. What caused a longer reaction time for visual than auditory cue? This is because an auditory stimulus only takes 8-10 msec to reach the brain (Kemp et al., 1973), but a visual stimulus takes 20-40 msec (Marshall et al., 1943).
In general, there are other factors that slow down reaction time in both visual and auditory stimuli including the state of attention or muscular tension. Moderate muscle tension seems to shorten the reaction time according to Davranche et al. (2006).
Reaction time also becomes more variable with age (Hultsch et al., 2002; Gorus et al., 2008). Simple reaction time shortens from infancy into the late 20s, then increases slowly until the 50s and 60s, and then lengthens faster as the person gets into his 70s and beyond (Welford, 1977). Our subjects were both in their mid 20’s as they age we would expect their mean reaction times to increase.
In almost every age group, males have faster reaction times than females (Noble et al., 1964; Welford, 1980). In our limited study, the female had faster reaction times for auditory and prompted auditory while the male had a faster reaction time for visual and predicted auditory.
Sanders (1998) studies show that when subjects are new to a reaction time task, their reaction times are less consistent than when they've had an adequate amount of practice. Also, if a subject makes an error (like pressing the spacebar before the stimulus is presented), subsequent reaction times are slower, as if the subject is being more cautious.
Welford (1968, 1980) found that reaction time gets slower when the subject is fatigued. Mental fatigue, especially sleepiness, has the greatest effect. Due to the strain of college life, the subjects may have been fatigued thus increasing their reaction times.
Welford (1980) and Broadbent (1971) reviewed studies showing that distractions increase reaction time. With several other groups around us performing the same experiment, same clicking noise and etc, distractions were inevitable thus possibly decreasing the reaction time. Trimmel and Poelzl (2006) found that background noise lengthened reaction time by inhibiting parts of the cerebral cortex.
Brebner and Welford (1980) report that reaction times are faster when the subject has been warned that a stimulus will arrive soon. This is exactly what is demonstrated in exercise 3 (prompted auditory). Our subjects displayed faster reactions times when they were warned with the word “ready” to prepare them to push the enter key.
Literature Cited
Broadbent, D. E. 1971. Decision and Stress. Academic Press, London.
Davranche, K., M. Audiffren, and A. Denjean. 2006. A distributional analysis of the effect of physical exercise on a choice reaction time task. Journal of Sports Sciences 24(3): 323-330.
Freeman, G. L. 1933. The facilitative and inhibitory effects of muscular tension upon performance. American Journal of Psychology 26: 602-608.
Gorus, E., R. De Raedt, M. Lambert, J. Lemper and T. Mets. 2008. Reaction times and performance variability in normal aging, mild cognitive impairment, and Alzheimer's disease. Journal of Geriatric Psychiatry and Neurology 21(3): 204-219.
Hultsch, D. F., S. W. MacDonald and R. A. Dixon. 2002. Variability in reaction time performance of younger and older adults. The Journals of Gerontology, Series B 57(2): 101.
Kemp, B. J. 1973. Reaction time of young and elderly subjects in relation to perceptual deprivation and signal-on versus signal-off condition. Developmental Psychology 8: 268-272.
Marshall, W. H., S. A. Talbot, and H. W. Ades. 1943. Cortical response of the anaesthesized cat to gross photic and electrical afferent stimulation. Journal of Nerophysiology 6: 1-15.
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Welford, A. T. 1968. Fundamentals of Skill. Methuen, London.
Welford, A. T. 1977. Motor performance. In J. E. Birren and K. W. Schaie (Eds.), Handbook of the Psychology of Aging. Van Nostrand Reinhold, New York, pp. 450-496.
Welford, A. T. 1980. Choice reaction time: Basic concepts. In A. T. Welford (Ed.), Reaction Times. Academic Press, New York, pp. 73-128.
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