Detection of incremental and decremental bars at different locations across Mach bands and related stimuli

Two-alternative forced-choice procedures were used to measure the detectabi lity of bright and dark bars at various locations across luminance patterns that produced Mach bands. Detection performance was significantly affected by both dark and bright Mach bands: poor detection performance was observe d at locations near, but nt in, the Mach bands; relatively good detection p erformance at locations with the mach bands was caused by reliable changes in the width, depth, or symmetry of the bands produced by the signal bars. The changes were apparent with signals of lower luminance than that needed for detection in the plateau regions far from the bands, but because the cu es were not sufficiently reliable to allow errorless performance, unusually shaped psychometric functions were obtained. (C) 2000 Optical Scoiety of A merica [S0740-3232(00)01407-1] OCIS codes: 330.5000, 330.4060, 330.5510.