Date Published: May 21, 2019
Publisher: Public Library of Science
Author(s): Richard S. Hetley, Wm Wren Stine, Fred Kingdom.
When one views a square-wave grating and dichoptically changes the average luminance or contrast of the monocular images, at least three perceptual phenomena might occur. These are the Venetian blind effect, or a perceived rotation of the bars around individual vertical axes; binocular luster, or a perceived shimmering; and binocular rivalry, or an alternating perception between the views of the two eyes. Perception of luster and rivalry occur when the “light bars” in the grating dichoptically straddle the background luminance (one eye’s image has a higher luminance than the background and the other eye’s image has a lower luminance than the background), with little impact from the “dark bars.” Perception of rotation, on the other hand, is related to average luminance or contrast disparity, independent of whether or not the “light bars” straddle the background luminance. The patterns for perceived rotation versus binocular luster and binocular rivalry suggest at least two separate mechanisms in the visual system for processing luminance and contrast information over and above their differing physiological states suggested by their different appearances. While luster and rivalry depend directly on the relation between stimuli and the background, perceived rotation depends on the magnitude of the luminance or contrast disparity, as described by the generalized difference model.
Binocular vision allows us to detect differences between the two eyes’ views, extracting information from binocular disparities. (We use terminology from Macknik and Martinez-Conde . Binocular image and monocular image refer to an image pair presented to two eyes or an image presented to one eye, respectively. Dichoptic image refers to a binocular image that has a disparity or disparities between its two monocular images. Monoptic image refers to an image that has no disparity. Fused image, a term from general usage, refers to a participant’s unified perception of the presentation.) Geometric disparities are perhaps the best understood type of disparity giving rise to stereopsis . Luminance and contrast disparities, where the stimuli viewed by each eye are geometrically identical to one another, can give rise to at least three distinct perceptions depending in part on the geometry of the stimulus.
Our results, together with those of Hetley and Stine , expand our understanding of the processing of binocular luminance and contrast information. Hetley and Stine demonstrated for a fused image of a square-wave grating that perceived rotation varied as a function of the interocular difference in average luminance or contrast, while the brightness or perceived contrast varied with the interocular sum. Hence, distinct mechanisms control perceived rotation (the Venetian blind effect) versus brightness or perceived contrast for fused square-wave gratings presented with either average luminance or contrast disparities over and above the physiological states suggested by the different appearances of rotation versus the brightness or perceived contrast of the fused images (cf., ).