Compare and contrast the trichromatic theory and opponent process theory. List anatomical evidence for each and phenomena that each does not account for.

Question

What will be an ideal response?

Answer 1

The Trichromatic theory states that there are three main color processes from which we are able to perceive all colors. Evidence of the theory include the sensitivities of three different groups of cone receptors to a particular wavelength of light - short (blue), medium (green), or long (red). On the other hand, the opponent process theory states that humans are able to distinguish four pure colors - red, blue, green, and yellow - via two color receptors, rather than three. Rather than there being three groups of cells that are each sensitive to one of three wavelengths of light, according to the opponent process theory, cells respond in an opponent way to pairs of colors - red/green and blue/yellow. For example, some cells excite to red wavelengths of light but inhibit to green (and vice versa). Some cells excite to yellow but inhibit to blue (and vice versa). Evidence of the opponent process theory is found in how ganglion cells respond to wavelengths of light in an opponent fashion.
The trichromatic theory, however, cannot account for the perception of afterimages - a visual phenomenon that occurs after a stimulus has been removed. What is more, the theory cannot explain why the color of the afterimage is different than that of the actual stimulus. It also was unable to explain why yellow is often perceived by observers to be a pure color. The main criticism for the opponent process theory involved the idea of a chemical within the cells that broke down in response to one color but then regenerated in response to the complementary color.