133. Sensation and Perception: Color Vision Theory

Do not quote without permission. Note: Potential references to other articles in the encyclopedia are indicated by {}. These should be checked against the actual contents of other articles before publication. B r a i n a r d 2 A b s t r a c t Color vision is the ability to distinguish and identify lights and objects on the basis of their spectral properties. This entry presents several topics that underlie current theories of human color vision. These are trichromacy, opponency, adaptation, and color constancy. To understand the key ideas, it is useful to consider how information about color is transformed as it flows from the stimulus through the initial stages of the human visual system. At each image location, the color stimulus is specified by its spectral power distribution: the amount of power it contains at each wavelength. The classic color matching experiment shows that the normal human visual system is trichromatic: only three dimensions of spectral variation are coded by the visual system. The biological basis of normal trichromacy is that the retina contains three classes of cone photopigment. After the initial encoding of light by the cones, further processing occurs. Two aspects of this processing are particularly important. First, signals from three classes of cones are recombined to form a luminance and two color opponent channels. Second, there is adaptive signal regulation that keeps neural signals within their operating range and stabilizes the appearance of objects across changes of illumination (color constancy.) Color vision is the ability to distinguish and identify lights and objects on the basis of their spectral properties. This entry presents several key topics that underlie current theories of human color vision. These are trichromacy, color opponency, adaptation, and color constancy.