Symmetry and constancy in the perception of negative and positive luminance contrast

Abstract

The perception of suprathreshold luminance contrast was investigated by forced-choice psychophysical procedures that were designed to define contrast equivalence relations. Observers compared the perceived contrast of rectangular bars that were presented for 500 msec at 3.9 deg on opposite sides of the fovea. The results show a nearly symmetrical relation between the perception of negative and positive contrast that is largely invariant over four decades of background luminance. Thus, for any fixed background luminance, equal absolute contrasts evoke approximately equal perceived contrasts. Symmetry also held with variations in the width, the eccentricity, and the focus of the bars. Symmetry was investigated further by determining equivalent contrast relations for negative contrasts as a function of background luminance and by contrast scaling. These results show evidence for nearly perfect contrast constancy for targets of low to moderate contrast and departures form constancy for high-contrast targets. These new findings on negative contrast, symmetry, and contrast constancy are discussed in relation to underlying mechanisms for contrast perception and classic experiments on brightness and lightness constancy.

Directional Asymmetries and Age Effects in Human Self-Motion Perception

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Spatial and Temporal Properties of Cone Signals in Alert Macaque Primary Visual Cortex

“…Light decrements (OFF signals) are both more detectable and more readily discriminated than light increments (Walraven, 1977;Krauskopf, 1980;Whittle, 1986;Bowen et al, 1989;Kremers et al, 1993;Chichilnisky and Wandell, 1996), although the subjective contrast of both, as a function of the background luminance, is essentially symmetric (Burkhardt et al, 1984;Whittle, 1986). The higher salience of decrements is thought to reflect an adjustment by the visual system for the fact that, in the natural world, "the range of increment intensities exceeds the range of decrement intensities (increments may be arbitrarily intense while decrements are bounded by zero)" (Chichilnisky and Wandell, 1996).…”

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