Coding of Stereoscopic Depth Information in Visual Areas V3 and V3A

Abstract

The process of stereoscopic depth perception is thought to begin with the analysis of absolute binocular disparity, the difference in position of corresponding features in the left and right eye images with respect to the points of fixation. Our sensitivity to depth, however, is greater when depth judgments are based on relative disparity, the difference between two absolute disparities, compared to when they are based on absolute disparity. Therefore, the visual system is thought to compute relative disparities for fine depth discrimination. Functional magnetic resonance imaging studies in humans and monkeys have suggested that visual areas V3 and V3A may be specialized for stereoscopic depth processing based on relative disparities. In this study, we measured absolute and relative disparity tuning of neurons in V3 and V3A of alert fixating monkeys and we compared their basic tuning properties with those published previously for other visual areas. We found that neurons in V3 and V3A predominantly encode absolute, not relative, disparities. We also found that basic parameters of disparity tuning in V3 and V3A are similar to those from other extrastriate visual areas. Finally, by comparing single-unit activity with multi-unit activity measured at the same recording site, we demonstrate that neurons with similar disparity selectivity are clustered in both V3 and V3A. We conclude that areas V3 and V3A are not particularly specialized for processing stereoscopic depth information compared to other early visual areas, at least with respect to the tuning properties that we have examined.

Neural Activity in Cortical Area V4 Underlies Fine Disparity Discrimination

“…The representation of stereoscopic depth is in an imperfect relative frame of reference. The incompleteness matches the properties of a fraction of V4 neurons whose tuning curve for center disparity shifts with 90% of surround disparities (Umeda et al, 2007; for V2, see Thomas et al, 2002; for V3/V3A, see Anzai et al, 2011). The reference frame of fine stereoscopic depth perception might reflect the properties of the disparity representations in V4.…”

Deep Hierarchies in the Primate Visual Cortex: What Can We Learn for Computer Vision?

“…Note that the visual system is not organized in a strictly sequential hierarchy but there are shortcuts between levels of the hierarchy. There is a stream V1 → V2 (→ V3 5 ) → V4 to the ventral pathway and another stream V1 → V2 → MT to the dorsal pathway (figure 2). 5.…”

“…There is a stream V1 → V2 (→ V3 5 ) → V4 to the ventral pathway and another stream V1 → V2 → MT to the dorsal pathway (figure 2). 5. Not much is known about the role of V3, therefore we have not given any detailed information in this paper about V3.…”

Geospatial statistics of high field functional MRI reveals topographical clustering for binocular stereo depth in early visual cortex

“…By comparison, in extrastriate cortex of macaque, optical imaging reveals a near-to-far organization for disparity within the thick stripes of V2 14 and neurophysiology of extrastriate areas V2 15 , V3/V3A 16 and V5/MT 17 show evidence of clustering of neurons with similar disparity preferences.…”

“…By contrast, little is known of the organization for stereoscopic disparity in the human early visual cortex, despite the fact that there are some long-standing proposals for a disparity-based ordering in mammalian cortex 40 . Based on the literature from the macaque monkey, V2 14,15 , V3 16 and V3A 16 have a clustering of disparity selective neurons, and therefore could be expected to show clusters of voxels preferentially activated by a disparity-defined stimulus. Perhaps not surprisingly and consistent with recent work in human cortex 27 , we found that V3A shows the strongest evidence for cortical domains for processing stereoscopic depth, likely resulting from an ordered connectivity of disparity-selective neurons.…”