The chromatic contrast sensitivity myth

A universally accepted conclusion about contrast sensitivity functions (CSFs) for spatially modulated sinusoidal gratings is that luminance-modulated CSF's are band-pass, whereas equal luminance chromatically-modulated CSF's are low pass. This conclusion does not follow logically from available data. If the existing chromatic CSF's are compared to low level luminance CSF's, as they should be, then both classes of functions are low-pass. In order to be comparable (possibly) to high level luminance CSF's, chromatic CSF's should be centered at a point in chromaticity space that appears highly saturated, and modulation should be along the line that goes through that point from the spectrum locus to the white point. Very tentative results for two subjects with such purity modulated red gratings show small band-pass effects.