Color enhances Mach bands detection threshold and perceived brightness.

We have previously argued that unless color and luminance are shown to be processed independently, using isoluminant stimuli may not reveal the full contribution of color to visual functioning. Here we study the interaction of color and luminance in a task, Mach bands detection and perceived brightness, where color by itself is not effective at all. Subjects viewed luminance or color/luminance ramps and had to determine in either case the luminance contrast necessary for detecting Mach bands and, in another experiment, to compare the brightness of the bands in the luminance and in the combined displays. Isoluminant color displays did not generate any Mach bands, but the addition of color to the luminance display lowered Mach bands detection thresholds and enhanced their perceived brightness. It is thus concluded that the failure to perceive Mach bands in an isoluminant display is not indicative of the lack of color contribution to spatial vision but rather indicates that the strong effect that color has on contrast enhancement mechanisms can be revealed if color and luminance are allowed to interact.