The color-opponent and broad-band channels of the primate visual system

Physiological, anatomical and psychophysical studies have identified several parallel channels of information processing in the primate visual system. Two of these, the color-opponent and the broad-band channels, originate in the retina and remain in part segregated through several higher cortical stations. To improve understanding of their function, recent studies have examined the visual capacities of monkeys following selective disruption of these channels. Color vision, fine- but not coarse-form vision and stereopsis are severely impaired in the absence of the color-opponent channel, whereas motion and flicker perception are impaired at high but not low temporal frequencies in the absence of the broad-band channel. The results suggest that the color-opponent channel extends the range of vision in the spatial and wavelength domains, and that the broad-band channel extends it in the temporal domain. Lesion studies also indicate that these channels must reach higher cortical centers through extrastriate regions other than just area V4 and the middle temporal area, and that the analysis performed by these two regions cannot be uniquely identified with specific visual capacities.