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be willing to bet on the correctness of the answer. Move a step toward the class
and slightly more in front of the volunteer (imagine you are moving on an arching
track that would eventually place you directly in front of the volunteer) and ask the
same question. Continue to move, one small step at a time, along the arc until
the volunteer is certain of the object’s color. You may want to pause before each
step, briefly conceal the object, and give the volunteer a chance to relax the eyes.
Make sure the volunteer is staring at the fixation point again before proceeding.
DISCUSSION
You will find that most participants have excellent peripheral vision, as reflected
in their ability to recognize that the object is present even when it is far off to
the side. However, for most people, it will take several small steps before they
can recognize the object’s color (most will first say it is black, because they
are seeing it only with rods). The students will be surprised at how close to the
center of the visual field the object must be before its color is clearly apparent. In
real life, we perceive color in the periphery of the visual field because the brain
remembers what color belongs there or makes an assumption about the likely
color (e.g., the sky is usually blue). In this demonstration, however, there is no
way for the brain to accurately guess the color of the object.
If the expected sequence of results does not occur, it is probably because
the participant lost fixation or made a lucky guess about color. To confirm the
distribution of rods and cones and their color sensitivity, you can run more trials
using different colors.
You can make this demonstration an active learning experience by asking students
to predict the results of this procedure and to justify their predictions on the basis
of material presented in class or in the textbook. Another option is to divide the
class into teams of three and have them conduct the procedure, perhaps using
objects of different sizes and colors, held at differing distances. Team members
can take turns acting as volunteer, experimenter, and data recorder (whose job is
to note the point on each trial where the object is first detected, correctly named,
and its color identified). Afterward, teams can be asked to report their results to
the class, including the effect of object size and distance, and to suggest plausible
explanations for the discrepant data (e.g., individual differences in retinal anatomy,
restricted peripheral vision, or less fixation during a trial).
REFERENCES AND SUGGESTED READING
Bernstein, D. A., Penner, L. A., Clarke-Stewart, A., & Roy, E. J. (2008).
Psychology (8th ed.). Boston: Houghton Mifflin.
Goldstein, E.B. (2007). Sensation and perception (7th ed.). Belmont, CD:
Thomson Wadsworth.
Mollon, J. D., Pokorny, J., & Knoblauch, K. (2003). Norman and defective colour
vision. New York, NY: Oxford University Press.
Wolfe, J. M., Kluender, K. R., Levi, D. M., Bartoshuk, L. M., Herz, R. S, Klatzky, R.
L., & Lederman, S. J. (2006). Sensation and perception. Sunderland, MA:
Sinauer Associates.
Copyright © 2008 by the American Psychological Association. The official citation
that should be used in referencing this material is:
Blair-Broeker, C. T., & Bernstein, D. A. (2008). Distribution of rods, cones, and
color vision in the retina. In J. T. Benjamin, Jr. (Ed.), Favorite activities for
the teaching of psychology. Washington, DC: American Psychological
Association.
No further reproduction or distribution is permitted without written permission from the
American Psychological Association.
(activity 2.1 continued from previous page)
activities