Visual Reaction Time
Nervous responses to environmental stimuli are necessarily rapid events, taking a small fraction of a second to be completed. The stages in such a response involve:
(1) transduction of the environmental stimulus into a nervous impulse (rods and cones)
(2) processing in the neurons of the retina (bipolar and ganglion cells)
(3) transmission of the impulse to the thalamus
(4) relaying of impulse to the visual cortex via optic radiations
(5) visual association region recognizes the meaning of the visual impulses
(6) transmission of impulse from visual association region to precentral gyrus
(7) transmission of the motor impulse from precentral gyrus to muscles of hand
(8) effecting the movement through the contraction of muscles.
The length of time required for the sum of these steps can be measured by a simple procedure measuring the visual reaction involved in catching a dropping ruler. By applying a simple law of the acceleration of gravity, the distance which the ruler dropped can be converted into the amount of time required for the completion of the visual reaction.
meter stick (or a yard stick)
card with horizontal line taped to wall at a convenient height
calculator with square root function
1. Experimenter holds meter stick with 50 cm mark on line of card, zero end of stick down. Be careful to line up the ruler exactly on the 50.0 cm mark. (The experiment can be done with a yard stick with a little additional conversion, and using a different equation for inches.)
2. Subject places thumb and forefinger on either side of ruler, near, but not touching it.
3. Experimenter asks to be certain that subject is ready, then within a few seconds releases ruler as cleanly as possible (no hints as to release, drop ruler straight down).
4. Subject grasps ruler as soon as possible after its release, and holds it against the wall where caught (do not move it once it is caught).
5. Experimenter reads the position of the line on the ruler to the nearest tenth of a centimeter (66.0 cm in the image to the left), subtracts 50 cm from that to get the distance the ruler dropped , and records the data in the notebook in cm (16.0 cm dropped in this example). Repeat at least five times to determine an accurate average. (You may drop the fastest and slowest reactions to see how that affects it)
6. Convert each distance dropped into milliseconds required for the visual reaction, then average the time for the visual reaction for the five determination. Use the equation below. A drop of 16.0 cm is equivalent to a visual reaction time of 180 milliseconds. See spelled out calculations below.
The distance dropped is converted into milliseconds by the following equation:
EXAMPLE CALCULATIONS FOR NUMBERS SHOWN IN THE ILLUSTRATIONS:
1) The ruler was caught at the 66.0 cm point, therefore the distance dropped was 16.0 cm
2) 2 times 16.0 cm is equal to 32 cm.
3) 32 cm divided by 980 cm/sec2 equals 0.03265 seconds2
4) The square root of 0.03265 seconds2 is equal to 0.1807 seconds.
5) 0.1807 seconds times 1000 msec/second equals 180 milliseconds visual reaction time.
ASSIGNMENT: PERFORM AN EXPERIMENT AT HOME
Design an experiment to test the effects of time of day, fatigue, time of the month, various agents etc., on your friends and/or family members: Record the data and perform the calculations in your notebook.Test the visual reaction time in triplicate for at least five different determinations.
Determine effects of various agents (caffeine, alcohol, ephedrine, etc.) on reflex time by measuring visual reaction before administering the agent, then repeat the determination after administration. Look for increasing effects with increasing amounts of the agent.
Repeat 10 or more times to look for learning and/or fatigue.
Conduct population studies to look for effects on reflex time of age, sex, handedness, etc.
TO DO THIS EXPERIMENT WITH A YARD STICK:
1) Line up the 10.0 inch mark on the yard stick with the wall line and the 0 inch end of the yard stick at bottom.
2) After the drop, read to the nearest 1/16th of an inch.
3) Convert the fraction to decimals of an inch, subtract 10 inches from reading. Substitute 385.8 inches/sec2 for 980 cm/sec2 for acceleration of gravity in the formula: