Abstract

Measurements of psychophysical thresholds to chromatic spots presented on a white background purport to demonstrate the existence of chromatic and luminance channels. We measured thresholds to such stimuli of the phasic, magnocellular (MCL) and the tonic, wavelength-opponent parvocellular (POL), cells of the macaque lateral geniculate nucleus. Spectral sensitivity of MCL cells approximated the V function. Wtih 4° spots, blue on-center and red on-center PCL cells were the most sensitive at the spectral ends, while in midspectrum MCL cells were somewhat more sensitive than the most sensitive PCL cells; with achromatic stimuli MCL cells were substantially more sensitive than PCL cells. With small spots, sensitivity of the different opponent cells decreased substantially at the spectral ends to become close to or slightly higher than that of MCL cells. Psychophysical thresholds with human subjects at similar retinal eccentricities with similar spot sizes could be accounted for by assuming the most sensitive cells were responsible for detection, supporting the notion that different cell classes support detection in different stimulus conditions.

© 1985 Optical Society of America