Color vision mechanisms in monkey striate cortex: simple cells with dual opponent-color receptive fields.

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Abstract
Single cells in the monkey''s [Macaca mulatta] visual cortex were recorded with tungsten microelectrodes and those neurons that were sensitive to the color of the stimulus were studied. In the primate striate cortex there are 4 classes of color-coded cells. The cells described in this paper had simple receptive fields with a dual opponent-color organization. The fields of these cells consisted in most cases of a central rectangular strip containing 1 red-green opponent-color system and 2 antagonistic flanks with the reverse opponent arrangement. Sometimes the field contained only 2 subdivisions which lay adjacent to one another. These cells were most sensitive to the simultaneous presentation of two complementary colors falling on oppositely organized parts of the receptive field. They are probably involved in the perception of stimultaneous color-contrast phenomena and may have some relationship to the McCullough effect. Spectral sensitivity studies utilizing chromatic adaptation with red or blue light revealed that the green-sensitive and red-sensitive cone processes underlying the on-off responses had peaks at 520-540 nm and 575-580 nm, respectively. The orientation selectivity of a cell to colored bars was not altered by a monochromatic background light or by changing the wavelength of the stimulus. Multiple-unit recordings from a concentric cell and one of its presumed afferents yielded useful information regarding its possible synaptic inputs. In 26 instances recording were made simultaneously from a concentric cell and a simple cell, both of which were color sensitive. The ocular preference, the laminar locaton, the multiple-unit studies and the simple receptive-field organization indicated that these cells are receiving synaptic contacts directly from the opponent-color concentric cortical cells studied earlier. The simple cells are the 2nd stage in the cortical integration of color.