Contrast and lustre: A model that accounts for eleven different forms of contrast discrimination in binocular vision

Abstract

Our goal here is a more complete understanding of how information about luminance contrast is encoded and used by the binocular visual system. In two-interval forced-choice experiments we assessed observers' ability to discriminate changes in contrast that could be an increase or decrease of contrast in one or both eyes, or an increase in one eye coupled with a decrease in the other (termed IncDec). The base or pedestal contrasts were either in-phase or out-of-phase in the two eyes. The opposed changes in the IncDec condition did not cancel each other out, implying that along with binocular summation, information is also available from mechanisms that do not sum the two eyes' inputs. These might be monocular mechanisms. With a binocular pedestal, monocular increments of contrast were much easier to see than monocular decrements. These findings suggest that there are separate binocular (B) and monocular (L,R) channels, but only the largest of the three responses, max(L,B,R), is available to perception and decision. Results from contrast discrimination and contrast matching tasks were described very accurately by this model. Stimuli, data, and model responses can all be visualized in a common binocular contrast space, allowing a more direct comparison between models and data. Some results with out-of-phase pedestals were not accounted for by the max model of contrast coding, but were well explained by an extended model in which gratings of opposite polarity create the sensation of lustre. Observers can discriminate changes in lustre alongside changes in contrast.

Interocular difference thresholds are mediated by binocular differencing, not summing, channels

“…However, we found that the results from both experiments were well described by a simpler model in which a single, linear binocular differencing channel is followed by a standard nonlinear transducer that is expansive for small signals but strongly compressive impression of luster, a cue that has been argued to enable detection of interocular differences (Formankiewicz & Mollon, 2009;Yoonessi & Kingdom, 2009;Malkoc & Kingdom, 2012;Jennings & Kingdom, 2016;Kingdom et al, 2018). Recent studies have suggested models for interocular difference detection based on luster (Georgeson et al, 2016;Jennings & Kingdom, 2016) and have furthermore demonstrated that interocular difference detection is an adaptable dimension of vision (Kingdom et al, 2018).…”

“…This leaves open the question why a horizontally oriented Bþ channel is not involved. Recently, Georgeson et al (2016) put forward a model of binocular combination to account for the appearance of dichoptic mixtures of luminance contrasts and discrimination-threshold measures obtained in dichoptic masking experiments. They suggested that three channels were involved, two monocular (call these L and R) alongside the binocular summing Bþ channel.…”

Decoding eye-of-origin outside of awareness

“…It therefore appears that humans have conscious access to information from their binocular visual system besides a mandatory binocular fusion of the two eyes' inputs. This information could include stereo depth from occlusion (McLoughlin and Grossberg, 1998), a binocular differencing channel (Li and Atick, 1994;May et al, 2012), or a 'lustre channel' that codes differences in luminance polarity across the eyes (Georgeson et al, 2016).…”

Binocular functional architecture for detection of contrast-modulated gratings

“…6), but in the first-order model ) the monocular channels are not influenced by the other eye, and always have a weight of 1.0. The idea of computing the max over monocular and binocular channel responses has also been successfully applied to explain dichoptic (first-order) contrast discrimination and contrast matching (Georgeson, Wallis, Meese, & Baker, 2016).…”