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Spatial Stereoresolution for Depth Corrugations May Be Set in Primary Visual Cortex

Lookup NU author(s): Dr Fredrik Allenmark, Professor Jenny Read

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Abstract

Stereo "3D" depth perception requires the visual system to extract binocular disparities between the two eyes' images. Several current models of this process, based on the known physiology of primary visual cortex (V1), do this by computing a piecewise-frontoparallel local cross-correlation between the left and right eye's images. The size of the "window" within which detectors examine the local cross-correlation corresponds to the receptive field size of V1 neurons. This basic model has successfully captured many aspects of human depth perception. In particular, it accounts for the low human stereoresolution for sinusoidal depth corrugations, suggesting that the limit on stereoresolution may be set in primary visual cortex. An important feature of the model, reflecting a key property of V1 neurons, is that the initial disparity encoding is performed by detectors tuned to locally uniform patches of disparity. Such detectors respond better to square-wave depth corrugations, since these are locally flat, than to sinusoidal corrugations which are slanted almost everywhere. Consequently, for any given window size, current models predict better performance for square-wave disparity corrugations than for sine-wave corrugations at high amplitudes. We have recently shown that this prediction is not borne out: humans perform no better with square-wave than with sine-wave corrugations, even at high amplitudes. The failure of this prediction raised the question of whether stereoresolution may actually be set at later stages of cortical processing, perhaps involving neurons tuned to disparity slant or curvature. Here we extend the local cross-correlation model to include existing physiological and psychophysical evidence indicating that larger disparities are detected by neurons with larger receptive fields (a size/disparity correlation). We show that this simple modification succeeds in reconciling the model with human results, confirming that stereoresolution for disparity gratings may indeed be limited by the size of receptive fields in primary visual cortex.


Publication metadata

Author(s): Allenmark F, Read JCA

Publication type: Article

Publication status: Published

Journal: PLoS Computational Biology

Year: 2011

Volume: 7

Issue: 8

Print publication date: 18/08/2011

Date deposited: 07/11/2011

ISSN (print): 1553-734X

ISSN (electronic):

Publisher: Public Library of Science

URL: http://dx.doi.org/10.1371/journal.pcbi.1002142

DOI: 10.1371/journal.pcbi.1002142


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