Neurons in Striate Cortex Signal Disparity in Half-Matched Random-Dot Stereograms

Abstract

Human stereopsis can operate in dense "cyclopean" images containing no monocular objects. This is believed to depend on the computation of binocular correlation by neurons in primary visual cortex (V1). The observation that humans perceive depth in half-matched random-dot stereograms, although these stimuli have no net correlation, has led to the proposition that human depth perception in these stimuli depends on a distinct "matching" computation possibly performed in extrastriate cortex. However, recording from disparityselective neurons in V1 of fixating monkeys, we found that they are in fact able to signal disparity in half-matched stimuli. We present a simple model that explains these results. This reinstates the view that disparity-selective neurons in V1 provide the initial substrate for perception in dense cyclopean stimuli, and strongly suggests that separate correlation and matching computations are not necessary to explain existing data on mixed correlation stereograms.

Current models cannot account for V1's specialisation for binocular natural image statistics

“…In order to quantify this, we compute the regression slope (type II regression, [Draper and Smith, 2014]) between the correlated and anticorrelated response. We will refer to this metric as the relative anticorrelated response of the cell (note that this is different from the metric used to quantify anticorrelated attenuation in [Cumming and Parker, 1997], but the same as that used by [Henriksen et al, 2016b]). Figure 4b shows graphically how the relative anticorrelated response quantifies the degree to which dispartiy tuning is reduced for anticorrealted stimuli.…”

“…One interesting property of these neurons has been hard to capture with the model: when presented with anticorrelated random dot patterns, neuronal responses are less strongly modulated by disparity than in correlated patterns [Cumming and Parker, 1997]. This anticorrelated attenuation is thought to represent the fact that these stimuli cannot arise in natural viewing and hence represent a specialisation for the statistics of natural binocular inputs [Haefner and Cumming, 2008, Henriksen et al, 2016b].…”

Specialization of mid-tier stages of dorsal and ventral pathways in stereoscopic processing

“…This explanation is possible because stimuli with non-preferred motion parameters decrease the strength of disparity selectivity for cRDSs in MT (Palanca and DeAngelis, 2003). At least in V1, neurons with weaker disparity selectivity for cRDSs exhibit responses closer to the correlation-based prediction (Henriksen et al 2016b). However, we found no correlation between area ratio and the disparity selectivity Figures S4C,D).…”

“…Adding expansive nonlinearity to disparity energy models can achieve the transformation under some conditions (Doi and Fujita, 2014;Lippert and Wagner, 2001). Although the additional nonlinearity must be only part of the full mechanism, it has psychophysical (Doi et al, 2013;Henriksen et al, 2016a) and physiological support (Henriksen et al, 2016b). A key constraint of this mechanism is that the energy-model units should have even-symmetric, but not odd-symmetric, disparity tuning.…”

Interocular correlation sensitivity and its relationship with stereopsis

“…This computation could be mediated by on and off channels subserving image similarities and differences between the two eyes (Kingdom, 2012 ; Li & Atick, 1994 ; May, Zhaoping, & Hibbard, 2012 ). For a given disparity, the degree of correlation in the signals between the two eyes provides, in normal observers, a measure of the strength of the depth percept (Cisarik & Harwerth, 2008 ; Doi, Tanabe, & Fujita, 2011 ; Henriksen, Cumming, & Read, 2016a ; Henriksen, Read, & Cumming, 2016b ; Julesz & Tyler, 1976 ; Tyler & Julesz, 1980 ). We were interested in providing a measure of the quality of binocular vision without disparity processing.…”