Sensitivity of macaque retinal ganglion cells and human observers to combined luminance and chromatic temporal modulation.

We measured the sensitivity of macaque retinal ganglion cells and human subjects to luminance and chromatic modulation and to two combined conditions as a function of temporal frequency. For both physiological and psychophysical data, we compared the sensitivities to luminance and chromatic modulation with the sensitivities in the combined conditions, using an additivity measure. When the physiological and the psychophysical data were taken together, the results suggested that under the combined conditions psychophysical sensitivity was the envelope of independent achromatic and chromatic mechanisms with physiological substrates in the magnocellular and the parvocellular pathways, respectively. In the combined conditions tested, sensitivity appeared to be set by a chromatic channel below 3 Hz and an achromatic channel above this frequency. This hypothesis was supported by a comparison of detection sensitivities with discrimination thresholds for the presence of chromatic alternation.