NEURONAL MECHANISMS OF COLOR CATEGORIZATION IN AREAS V1, V2 AND V4 OFMACAQUE MONKEY VISUAL-CORTEX

A landmark study conducted by Berlin and Kay (Basic Color Terms, Unive rsity of California Press, Berkeley, 1969, pp. 1-12) demonstrates that well-developed languages contain exactly 11 basic color terms. The ba sic colors (8 chromatic and 3 achromatic) are situated in specific loc ations of color space, suggesting a fixed relationship between specifi c hue and luminance. To determine the physiologic origins of the basic colors, we have studied the responses of cells in visual cortical are as V1, V2 and V4 of the behaving macaque monkey, using chromatic and a chromatic stimuli of varying luminance. A total of 569 cells (291 from V1, 205 from V2, 73 from V4) were obtained, and classified as 'B' (br ight; 43-50% of the total cells in each area), 'D' (dark; 6-12% of the total), and 'B/D' (bright/dark; 27-28% of the total) color or non-col or cells according to each cell's color/luminance preference in relati on to the neutral gray background. About two thirds of 'B' cells in ea ch area were color specific, whereas the proportion of color cells in 'B/D' and 'D' categories was lower. In all three areas (V1, V2, V4), c olor cells with preferences for midspectral colors (such as yellow, li me and green) also preferred high luminance levels, while color cells with preferences for endspectral colors (such as red and blue) respond ed preferentially to luminance levels closer to background. The data p rovide evidence for categorical color perception within the visual sys tem, as well as providing a physiological basis for the increased sali ency of endspectral contours observed at equiluminance in psychophysic al studies.