Abstract
Stereoscopic vision delivers a sense of depth based on binocular information but additionally acts as a mechanism for achieving correspondence between patterns arriving at the left and right eyes. We analyse quantitatively the cortical architecture for stereoscopic vision in two areas of macaque visual cortex. For primary visual cortex V1, the result is consistent with a module that is isotropic in cortical space with a diameter of at least 3 mm in surface extent. This implies that the module for stereo is larger than the repeat distance between ocular dominance columns in V1. By contrast, in the extrastriate cortical area V5/MT, which has a specialized architecture for stereo depth, the module for representation of stereo is about 1 mm in surface extent, so the representation of stereo in V5/MT is more compressed than V1 in terms of neural wiring of the neocortex. The surface extent estimated for stereo in V5/MT is consistent with measurements of its specialized domains for binocular disparity. Within V1, we suggest that long-range horizontal, anatomical connections form functional modules that serve both binocular and monocular pattern recognition: this common function may explain the distortion and disruption of monocular pattern vision observed in amblyopia.This article is part of the themed issue ‘Vision in our three-dimensional world’.
Highlights
Binocular stereoscopic vision is wholly dependent on the ability of the nervous system to register the presence of small differences in the exact positioning of visual features on the left and right retinae
On the basis of the measurements of sensitivity to horizontal disparity in cortical area V1, we suggest that V1 is organized for stereoscopic processing into a functional module about 3–4 mm across
The only cortical area so far discovered whose neurons appear to suppress fully the inverted stereo signal is in temporal cortex [21], area V4 in the ventral stream appears to suppress the inverted response partially [22], as do the neurons in V1 [85] to a lesser degree. This suggests that further research into ventral stream function is needed to resolve these questions. This analysis and review has focused on the important role of stereoscopic vision as a detector of patterns that correspond between the left and right eyes
Summary
Binocular stereoscopic vision is wholly dependent on the ability of the nervous system to register the presence of small differences in the exact positioning of visual features on the left and right retinae. In a crowded set of features with multiple similar features, the brain must find the correct matches between pairs of features (shown by the linking arrow between the left and right eye images in figure 1b), otherwise depth cannot be recovered accurately. Julesz highlighted this ‘correspondence problem’, as it became subsequently known [4], with his invention of the random-dot stereogram. Unless the neural mechanisms can establish this local matching, the brain will be unable to detect any higher-order structural relationships, which in the case of stereo vision reveal the size and shape of the figure defined by the differences in binocular disparity, as well as the figure’s depth profile. This paper will analyse the architecture and neural connections of the visual cortex that underlie the establishment of stereoscopic correspondence in binocular vision
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