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
(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 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.

EQUIPMENT:

meter stick (or a yard stick*)
card with horizontal line taped to wall at a convenient height

PROTOCOL:

1. Experimenter holds meter stick with 50 cm mark on line of card, zero end of stick down.
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). Experimenter reads the position of the line on the ruler to the nearest mm, subtracts 50 cm from it, and records the distance the ruler dropped in cm. Repeat at least five times to determine an accurate average. (You may drop the fastest and slowest reactions to see how that affects it)
5. The distance dropped is converted into milliseconds by the following equation:

Assignment at home: test the visual reaction time in triplicate at least five different times. Design an experiment to test the effects of time of day, fatigue, time of the month, or various agents on your friends and/or family: Record the data and perform the calculations in your notebook.

For example: Determine effects of various agents (caffeine, alcohol, etc.) on reflex time. 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.

* Line up with 10 inch mark, 0 inch at bottom. Convert 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.)