35.4: Luminance and Spatial-Frequency Interaction in the Perception of Contrast

摘要

To study the interaction of luminance and spatial frequency effects on apparent perception of Supra-threshold contrast, four subjects matched the appearance of Gabor patches at different luminances and frequencies. The contrast of a 1- octave Gabor test patch at one of 5 frequencies and at one of 7 mean luminance levels was matched to a standard patch of 3 c/deg at 50 cd/m~2 at a nominal contrast of 0.3. The test patch spatial frequency was randomly changed during each set of experiments, while the luminance was fixed. The subject regularly shifted fixation between the two target in response to a metronome tone every 1.5 sec. Contrast constancy was demonstrated across the whole luminance range for all but the two highest frequencies. For 8 c/deg the perceived test contrast was reduced only below 2 cd/m~2. For 16 c/deg perceived contrast decreased linearly (with a slope of -1/2 on a log scale) with decrease in luminance across the entire luminance range. As at threshold, reduction in luminance across the levels commonly available on a CRT display has only minimal effects on low frequency Supra-threshold contrast perception. Unlike the results of dichoptic presentation, where contrast constancy is maintained over a wide range of luminances, the apparent contrast of high frequency features, in binocular free viewing condition, is rapidly reduced with a local reduction in screen luminance.