Four primaries are required to modulate independently the three types of cone and the rod photoreceptors. In order to work in a 4-primary colorimetric system, it is necessary to have accurate estimates of an individual observer's receptoral spectral sensitivities and prereceptoral filtering. A technique to evaluate whether an individual observer's receptoral sensitivities may be characterized as linear transforms of the Standard Observer's data for the colorimeter primaries is described. If the individual fulfills this prerequisite, the techinique allows compensation for prereceptoral filtering differences between the individual and the Standard Observer For two observers who fulfilled this requirement, temporal contrast sensitivity functions for the three cone types and the rods were measured at different luminance levels using the method of silent substitution Temporal contrast sensitivity functions for cones increased with luminance level from 0.5-50 photopic td. Temporal contrast sensitivity functions for rods increased with luminance level from 0.05 td (0.024 scotopic td) to 5 td (2.413 scotopic td), then decreased at 50 td (24.13 scotopic td). (C) 2000 John Wiley & Sons, Inc. Col Res Appl, 26, S69-S75, 2001.