Walsh & Hoyt: Parallels with Nonhuman Primates

Zeki first described color-selective neurons in area V4 of monkey. Wavelength selectivity has since been shown in other regions of macaque extrastriate cortex, including V2 and inferotemporal cortex. Nevertheless, most attention has been focused on the role of V4 in color perception. Several studies suggest that area V4 in monkeys may be the site at which color constancy is generated. Zeki reported that both V1 and V4 contained neurons with wavelength-selective responses, but only V4 had cells with responses that did not vary with the illumination and hence were specific for color rather than wavelength. Schein and Desimone described a possible mechanism by which the illuminant could be discounted: they found that responses of V4 cells to wavelengths in the classical receptive field were suppressed by similar wavelengths in a large surrounding region that could even extend into the ipsilateral hemifield. One lesion study has shown that color constancy is impaired by lesions of V4.