Mach-band attenuation by adjacent stimuli: experiment and filling-in simulations.

Mach bands are illusory bright and dark bands seen where a luminance plateau meets a ramp, as in half shadows or penumbras. It has previously been shown that Mach bands are attenuated by placing stimuli, such as bars, nearby. It was shown in an experiment in which Mach-band attenuation for bar and Craik-O'Brien stimuli was compared that they are equally effective in attenuating Mach bands. The results suggest that the abrupt luminance transition of a stimulus adjacent to a ramp is responsible for the attenuation. The findings are interpreted in terms of a recent filling-in model of brightness perception and the results of computer simulations of stimuli are shown.