But once the signal moves past the retina on its way to the brain, the cells respond in a way consistent with opponent-process theory (Land, 1959 Kaiser, 1997). For visual processing on the retina, trichromatic theory applies: the cones are responsive to three different wavelengths that represent red, blue, and green. Research has shown that they just apply to different levels of the nervous system. What do you see? This is known as a negative afterimage, and it provides empirical support for the opponent-process theory of color vision.īut these two theories-the trichromatic theory of color vision and the opponent-process theory-are not mutually exclusive. Stare at the white dot for 30–60 seconds and then move your eyes to a blank piece of white paper. You can test this concept using the flag in Figure 2. When color is involved in the stimulus, the color pairings identified in the opponent-process theory lead to a negative afterimage. For example, when you stare briefly at the sun and then look away from it, you may still perceive a spot of light although the stimulus (the sun) has been removed. An afterimage describes the continuation of a visual sensation after removal of the stimulus. Another implication is that this leads to the experience of negative afterimages. One of the implications of opponent processing is that we do not experience greenish-reds or yellowish-blues as colors. So, a cell that was excited by wavelengths associated with green would be inhibited by wavelengths associated with red, and vice versa. The basic idea is that some cells of the visual system are excited by one of the opponent colors and inhibited by the other. According to this theory, color is coded in opponent pairs: black-white, yellow-blue, and green-red. The trichromatic theory of color vision is not the only theory-another major theory of color vision is known as the opponent-process theory. (credit: modification of work by Vanessa Ezekowitz) This figure illustrates the different sensitivities for the three cone types found in a normal-sighted individual. The three types of cones are each receptive to one of the colors. According to the Young-Helmholtz trichromatic theory of color vision, shown in Figure 1, all colors in the spectrum can be produced by combining red, green, and blue. Each of these cone types is maximally sensitive to a slightly different wavelength of light. Normal-sighted individuals have three different types of cones that mediate color vision.
Let’s look at how color vision works and how we perceive three dimensions (height, width, and depth). We do not see the world in black and white neither do we see it as two-dimensional (2-D) or flat (just height and width, no depth). Describe how monocular and binocular cues are used in the perception of depth.Describe the trichromatic theory of color vision and the opponent-process theory.
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