Temporal integration of rod signals in luminance and chromatic pathways

We assessed how rod excitation (R) affects luminance (L+M+S) and chromatic [L/(L+M)] reaction times (RTs). A four-primary display based on the overlapped images of two spectrally-modified monitors, which allowed specific or combined [L+M+S+R, L/(L+M) + R] photoreceptor stimulation, was used to present a C-target stimulus differing from the background only by the selected stimulation. For the luminance pathway, rod input increased RTs, suggesting a suppressive rod-cone interaction. The responses of the chromatic pathway were faster when rods were involved, suggesting a major role of rods in mesopic color perception.