Matching and correlation computations in stereoscopic depth perception

Abstract

A fundamental task of the visual system is to infer depth by using binocular disparity. To encode binocular disparity, the visual cortex performs two distinct computations: one detects matched patterns in paired images (matching computation); the other constructs the cross-correlation between the images (correlation computation). How the two computations are used in stereoscopic perception is unclear. We dissociated their contributions in near/far discrimination by varying the magnitude of the disparity across separate sessions. For small disparity (0.03°), subjects performed at chance level to a binocularly opposite-contrast (anti-correlated) random-dot stereogram (RDS) but improved their performance with the proportion of contrast-matched (correlated) dots. For large disparity (0.48°), the direction of perceived depth reversed with an anti-correlated RDS relative to that for a correlated one. Neither reversed nor normal depth was perceived when anti-correlation was applied to half of the dots. We explain the decision process as a weighted average of the two computations, with the relative weight of the correlation computation increasing with the disparity magnitude. We conclude that matching computation dominates fine depth perception, while both computations contribute to coarser depth perception. Thus, stereoscopic depth perception recruits different computations depending on the disparity magnitude.

Weighted parallel contributions of binocular correlation and match signals to conscious perception of depth

“…In one series of experiments, we examined how the magnitude of binocular disparity affected the performance of disparity discrimination for graded anti-correlation [30]. When the disparity of the centre relative to the surround was +0.038 (a disparity within a range of fine stereopsis), the psychometric functions agreed with the prediction of the matching computation (figure 3b, leftmost).…”

“…This agrees with the manifestation of the correlation signal in vergence eye movement and psychophysical depth discrimination. aRDSs evoke only modestly inverted vergence response or depth judgement compared with cRDSs [18,30,37,85]. Compared with V1, a smaller fraction (approx.…”

“…The subjects' performance in the two experiments can be captured with a computational model in which correlation and matching computations operate in parallel and their signals are combined with variable relative weights (figure 3a) [30]. The model transforms a bivariate input (disparity sign, binocular match level) into a binary choice (near versus far).…”

Temporal channels and disparity representations in stereoscopic depth perception

“…The relative role of the two representations differs between fine and coarse depth perception (Doi, Tanabe, & Fujita, 2011). The match-based representation dominates fine depth perception, whereas both match-based and correlation-based representations contribute to coarse depth perception.…”

“…Two types of neural representations of binocular disparity-correlation-based and match-based representations-underlie stereoscopic depth perception (Cumming & Parker, 1997;Doi, Tanabe, & Fujita, 2011;Janssen, Vogels, Liu, & Orban, 2003;Krug, Cumming, & Parker, 2004;Kumano, Tanabe, & Fujita, 2008;Parker, 2007;Tanabe, Umeda, & Fujita, 2004). These representations are characterized by disparity tuning functions of the neurons underlying perceptual decisions.…”