Contrast perception across changes in luminance and spatial frequency

Abstract

The interaction of the effects of luminance and spatial frequency on perception of suprathreshold contrast was studied with use of a contrast-matching paradigm. Four subjects matched the appearance of Gabor patches at different luminances and spatial frequencies. The contrast of a 1-octave Gabor test patch at one of five frequencies [1-16 cycles/degree (c/deg) in 1-octave steps] and at one of seven mean luminance levels (0.5-50 cd/m2 in 1/3-log-unit steps) was matched, by the method of adjustment to a standard patch of 3 c/deg at 50 cd/m2 at a nominal contrast of 0.3. For each block of trials the spatial frequency of the test patch was randomly changed (three repetitions at each frequency per block) while the luminance was fixed. The subject regularly shifted fixation between the two targets in response to a metronome tone every 1.5 s. Contrast constancy was demonstrated across the entire luminance range tested for all but the two highest frequencies. For 8 c/deg the perceived test contrast was reduced only when the luminance was less than 2 cd/m2. For 16 c/deg, perceived contrast decreased linearly (with a slope of -1/2 on a log scale) with decreases 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 suprathreshold contrast perception. However, the apparent contrast of high-frequency features, in binocular free-viewing conditions, is rapidly reduced with a local reduction in screen luminance. This effect has important implications for visual models used in image-quality analysis.

Neuronal nonlinearity explains greater visual spatial resolution for darks than lights

“…In fact, the modulation transfer function is probably the most common measure of how faithfully a lens, a human observer or a visual neuron reproduces the spatial frequency of a grating (27)(28)(29). Binary stimuli (light and dark luminance values) are also widely used to estimate spatiotemporal receptive fields (30)(31)(32)(33).…”

Quantitative Analysis of Functional Changes Caused by Pinhole Glasses

“…6,7 Decrease of luminance was related to deterioration of CS. 26,27 Pupil or pinhole size has a large effect on the optical transfer function of the eye, and if the pupil or pinhole size is fixed, transfer rate decreases more as frequency increases. 28,29 Accordingly, in our study, decrease of luminance by pinhole glasses caused general reduction of CS.…”

Contrast sensitivity to radial frequencies modulated by Jn and j n Bessel profiles

“…Only recently did Amidor (11) and Wilkinson et al (12) use the term radial frequency to refer to different meanings of modulations, some of them concerning modulations across the radius. Mainstream research seems to be more directed towards local filtering of spatial characteristics employing Gabor's or DOG functions as elementary stimuli, generally defined in Cartesian coordinates to probe local processing (e.g., [13][14][15][16][17][18][19]. Dodwell (20) has proposed a Lie transformation group model based on Hoffman's suggestion (21).…”