Abstract

The contribution of color to motion can be measured by finding the equivalent luminance contrast of color stimuli: the contrast of a moving luminance grating required to just null the notion of an equiluminous color grating, of the same spatial and temporal frequency, moving in the opposite direction. The equivalent contrast of color stimuli was highest at low temporal and spatial frequencies and was highest for red/green stimuli, intermediate for yellow/blue, and lowest for green/purple falling on the tritanopic confusion line. This new measure provided an excellent basis for identifying color-defective observers, since, unlike normals, they required little or no luminance contrast to null the motion of a chromatic stimulus, whether it was red/green, which they discriminate less well than normals, or blue/yellow, which they discriminate as well as normals. Additional tests showed that neither long-range motion processes, interneuron variability in equiluminance, phase lag, nor second harmonic distortion in the response contributed significantly to the motion perception. The contribution of color to motion appears to derive, at least in part, from an opponent-color input to direction-selection units. This input is absent for color-defective individuals.

© 1987 Optical Society of America