Demonstrations Supporting the Opponent-Processing Theory of Color Vision

Everyday we see color all around us. In the fall we see the leaves turn a beautiful red and orange, and in spring we watch flowers of purple, pink, and yellow blossom in open fields, parks, and our own backyards. Most people cannot imagine a world without color. But how is it that we're able to see color? How are we able to distinguish between a lime shade of green and a deep forest shade of green? And why is it that some people lack the ability to see color?

The opponent-process theory of color vision was proposed in 1874 by Ewald Herring in response to the issues of the former color vision theory, the Young-Helmholtz thichromatic theory (Klein & Throne, 2007). The more recent opponent-process theory proposed that the retina contained sensory receptors that work to detect color due to their arrangement in pairs of red and green, yellow and blue, and black and white. The idea is that if one of the set of pairs is stimulated, then the opposing pair will be inhibited, and then the color is processed and "encoded in terms of its proportion of red OR green, and blue OR yellow" (Hockenbury, 2010). Because each set of color sensitive neurons (receptors) work by inhibiting one of the two in the pair, the theory works to alleviate one of the Trichromatic Theory of Color Vision's biggest fault, a concept called "afterimage."

Afterimage is the first concept that demonstrates the opponent-process theory, and refers to the colors that linger after staring into one particular color. Hockenbury (2010) gives the example of staring at a green light, and then switching over to a white wall. Because you've worn out your green receptors they've temporarily become desensitized and essentially turn off. For this reason, when you switch your line of sight to a white wall, patches of red light can be seen. There is a bit more to this, the opponent-process theory works with the basic principles of color. Since white contains every color, the green and read are technically already available on the white wall, however, since the green receptors are worn out, only the red is activated, and thus seen on the white wall.

Another demonstration that supports the opponent-process theory is called simultaneous contrast or "lateral inhibition." Simultaneous contrast is a concept dealing with shadows and color contrast. More specifically, it states that two identical shades of grey will appear darker or lighter than one another when placed against a lighter or darker background. A grey set against a darker background will appear to be lighter, while a grey set against a light background will appear to be darker (Adelson, 2000). The grey against the light background will appear darker because the illumination behind it is brighter, and a darker colored background has the opposite effect.

The last demonstration supporting the opponent-process theory is called visualizing colors. Goldstein (2010) notes that it is easier for an individual to visualize two colors if they are from different sets. For example, it is easy for us to visualize something as greenish blue, but not greenish red, even though we can visualize a green tree with red apples. This is because the colors blue and green are from different sets of pairs (black/white, green/red, blue/yellow). However, green and red are from the same set, and thus it is nearly impossible to visualize an object that utilizes both receptors at the same time. The principle is that it is harder to see these colors next to one another.

References

Adelson, E.H. (2000). The New Cognitive Neurosciences, 2^nd Ed. Cambridge: MIT Press.

Goldstein, E.B. (2010). Sensation and perception (8^h ed.). Belmont: Wadsworth.

Hockenbury, S. E. (2010). Psychology, 5^th Ed. New York: Worth Publishers.

Klein, S. B., & Thorne, B. M. (2007). Biological Psychology. New York: Worth Publishers.

Ware, C. (N.d). Introduction to Color Vision. Retrieved November 11, 2009, from http://www.ccom.unh.edu/vislab/VisCourse/ColorBasic.html