Binocular functional architecture for detection of contrast-modulated gratings

Abstract

Running head: Binocular summation for contrast modulationCorresponding author: m.a.georgeson@aston.ac.uk Highlights• Detection of contrast modulation (CM) shows full binocular summation • Similarity or dissimilarity of the carriers has no effect on summation • Out-of-phase envelopes don't cancel, but are a bit less detectable than monocular ones • Model: monocular envelope extraction, then contrast-weighted binocular summation • Monocular CM outputs in parallel with binocular ones; largest response wins AbstractCombination of signals from the two eyes is the gateway to stereo vision. To gain insight into binocular signal processing, we studied binocular summation for luminance-modulated gratings (L or LM) and contrast-modulated gratings (CM). We measured 2AFC detection thresholds for a signal grating (0.75 c/deg, 216msec) shown to one eye, both eyes, or both eyes out-of-phase. For LM and CM, the carrier noise was in both eyes, even when the signal was monocular. Mean binocular thresholds for luminance gratings (L) were 5.4dB better than monocular thresholdsclose to perfect linear summation (6dB). For LM and CM the binocular advantage was again 5-6dB, even when the carrier noise was uncorrelated, anti-correlated, or at orthogonal orientations in the two eyes. Binocular combination for CM probably arises from summation of envelope responses, and not from summation of these conflicting carrier patterns. Antiphase signals produced no binocular advantage, but thresholds were about 1-3dB higher than monocular ones. This is not consistent with simple linear summation, which should give complete cancellation and unmeasurably high thresholds. We propose a three-channel model in which noisy monocular responses to the envelope are binocularly combined in a contrast-weighted sum, but also remain separately available to perception via a max operator. Vision selects the largest of the three responses. With in-phase gratings the binocular channel dominates, but antiphase gratings cancel in the binocular channel and the monocular channels mediate detection. The small antiphase disadvantage might be explained by a subtle influence of background responses on binocular and monocular detection.3

Binocular summation revisited: Beyond √2.

“…Understanding how the visual system integrates different cues across the eyes, and how the findings for contrast apply to different domains, will require further study. However, we note that the same general framework for signal combination and suppression that we discuss here and in our other work ( Georgeson, Wallis, Meese, & Baker, 2016 ; Meese et al, 2006 ) has been successfully applied to understand binocular combination of cues such as motion ( Maehara, Hess, & Georgeson, 2017 ) and contrast modulation ( Georgeson & Schofield, 2016 ), as well as summation across space ( Meese & Summers, 2007 ), time, and orientation ( Meese & Baker, 2013 ), and also to make accurate predictions regarding neural responses ( Baker & Wade, 2017 ).…”

Binocular combination of luminance profiles

“…Different from our model that operates in 2D space along the whole signal path, the models proposed in Zhou et al ( 2014 ) and Georgeson and Schofield ( 2016 ) assumed a FRF (filter-rectify-filter) structure for each eye to extract the second-order signal (a vector) from a 2D stimulus representation, and then, the two eyes' second-order signals were contrast-weighted and summed (vector summation) for binocular output.…”

“…The final output was assumed to be the maximum of the three channels. Its monocular channels play a key role in preventing cancellation at the antiphase disparity (180°), providing more reasonable predictions of CM detection data when the CM gratings were 180° out of phase in the two eyes (Georgeson & Schofield, 2016 ). However, when CM phase disparity is 0°–90°, its binocular channel always wins in the maximum operation, making the elaborated model identical to Zhou et al's model.…”

“…When TCE ≫ threshold and is equal in the two eyes, all five nested models (see Model section) have the property that the two eyes have equal weight in the binocular combination. With this property, all five models predict “linear” summation of CM gratings with identical CC in the two eyes (Georgeson & Schofield, 2016 ; Zhou et al, 2014 ), although the models themselves are nonlinear in general. In other words, the data in Figure 6A cannot distinguish among models—any model with a symmetric structure in the two eyes, can predict them.…”

“…The contrast-weighted summation model proposed by Zhou et al ( 2014 ) is similar to our first nested model in predictions of the results of Experiments 3a–3d. Georgeson and Schofield ( 2016 ) elaborated the Zhou model by adding two monocular channels in parallel to the binocular one. The final output was assumed to be the maximum of the three channels.…”