A nonlinear chromatic motion mechanism.

Previous research has demonstrated two categorically distinct mechanisms mediating apparent motion of kinematograms composed of eccentricity-confined, randomly placed Gabor micropatterns: a quasi-linear mechanism operating for high micropattern densities and short time separations, and a nonlinear mechanism operating at low micropattern densities or longer time separations. Here we compare the performance of these two mechanisms using color (isoluminant) and luminance-defined stimuli. When these stimuli are defined only by their color contrast, the response of the quasi-linear mechanism is severely impaired, while the nonlinear mechanism remains fully operative. This result further strengthens the dichotomy between the two kinds of motion perception, and suggests that when color vision supports motion perception it does so primarily, or perhaps entirely, via a nonlinear mechanism.