Mechanisms for chromatic discrimination in the macaque LGN

Abstract

Combinations of responses of some types of spectrally-opponent sustained cell of the macaque lateral geniculate nucleus (LGN) may be related to equidistant color space. Response curves of such cells to stimuli of different luminance ratios and wavelengths show striking similarities to opponent coordinates of the new SVF color difference formula. 1 Mathematical simulation of the responses of these cells to a variety of color stimuli is possible through computation of cone excitations and subsequent sums and differences of cone signals. When the response functions thus obtained for cells are used to replace the coordinates of the SVF diagram, depending on the choice of cells, the distributions of equiluminous stimuli with the same sensory differences from an achromatic stimulus approximate ellipses or circles about the white point, and loci of constant hue approximate straight lines. This indicates possible roles of these cell types for color scaling in primates. Improved uniformity may be obtained by including more LGN cell types with best responses to other luminance ratios and other directions of color space, the combination of responses probably occurring at a later stage.