Linearity of hue cancellation in sex-linked dichromacy

The results of several recent studies concur in the finding that for normal trichromats red-green hue-cancellation data obey linearity properties over rather general conditions, but for most observers yellow-blue hue-cancellation data do not. It is of interest to examine the question of cancellation linearity in sex-linked dichromats under the assumption that they represent reduced systems. We measured both the wavelength of the spectral achromatic point over a large range of intensities and yellow-blue hue-cancellation functions over the full spectrum and at several luminance levels in protanopes and deuteranopes. Both sets of data for the two types of dichromat satisfy linearity properties. These results are consistent with a model in which both cone receptor response functions have the same form. Implications for trichromatic opponent-response functions are considered.