The spatial transformation of color in the primary visual cortex of the macaque monkey

Perceptually, color is used to discriminate objects by hue and to identify color boundaries. The primate retina and the lateral geniculate nucleus (LG N) have cell populations sensitive to color modulation, but the role of the primary visual cortex (V1) in color signal processing is uncertain. We ree valuated color processing in V1 by studying single-neuron responses to lumi nance and to equiluminant color patterns equated for cone contrast. Many ne urons respond robustly to both equiluminant color and luminance modulation (color-luminance cells). Also, there are neurons that prefer luminance (lum inance cells), and a few neurons that prefer color (color cells). Surprisin gly, most color-luminance cells are spatial-frequency tuned, with approxima tely equal selectivity for chromatic and achromatic patterns. Therefore, V1 retains the color sensitivity provided by the LGN, and adds spatial select ivity for color boundaries.