6.3. Opponent Process Theory

The trichromatic theory explains color vision at the level of the cones. The opponent process theory is a complementary theory, which explains how color is coded at the level of the ganglion cells and lateral geniculate nucleus of the thalamus (Land, 1959; Kaiser, 1997). It states that color is coded in opponent pairs: black-white, yellow-blue, and green-red. The basic idea is that these cells in the visual system are excited by one of the opponent colors and inhibited by the other. So, a cell excited by wavelengths associated with green would be inhibited by wavelengths associated with red, and vice versa. Opponent processing helps to explain why we cannot experience greenish-reds or yellowish-blues as colors. The opponent process theory also explains our experience of negative afterimages. You have probably experienced an afterimage after looking directly at a lightbulb. You still see an image of the lightbulb (albeit of a different color) after you look away. The colors of the afterimage that we see can be predicted by the color pairings identified in the opponent-process theory. If we stare at a red color for a minute and then look at a white background, we will see green. Similarly, if we stare at green and look at a white background we see red (Figure 6.8)

Watch this video to help understand how color vision works: https://www.youtube.com/watch?v=poL7nDmqjmk