Reconstruction of equidistant color space from responses of visual neurones of macaques.

We demonstrate that a combination of responses of various types of spectrally opponent sustained cells 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 are similar to the first stage opponent coordinate functions of the new SVF color-difference formula [T. Seim and A. Valberg, Color Res. Appl. 11, 11 (1986)]. 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 corresponding coordinates of the SVF diagram, the distributions of equiluminous stimuli with the same sensory differences from an achromatic stimulus approximate ellipses about the white point, and loci of constant hue approximate straight lines. Improved uniformity may be obtained by linear combinations of these cells' outputs or by including more cell types with best responsiveness to other directions of color space. This indicates possible roles of LGN cell types for color scaling in primates, in that color scaling observed psychophysically is an implicit property of these cells' responses.