Effect of the short-wavelength-sensitive-cone mosaic and rods on the locus of unique green

A primary goal of this study was to establish whether the magnitude of the short-wavelength-sensitive- (S-) cone signal into the yellow/blue (Y/B) mechanism was influenced by the absolute or the relative numbers of S cones. This was assessed by measuring the locus of unique green for various test sizes at four eccentric locations chosen to exploit differences in the underlying mosaic of S cones. In general, the locus of unique green was unaffected by test size, retinal quadrant, or rod input but was influenced by retinal eccentricity. The locus of unique green shifted to shorter wavelengths as retinal eccentricity increased from 1 degrees to 8 degrees. The data do not support a model whereby the S-cone signal is determined by the absolute number of S cones, but a model based on the relative number of S cones cannot be eliminated.