Encoding of Binocular Disparity by Simple Cells in the Cat's Visual Cortex.
Ohzawa, Izumi, Gregory C. DeAngelis, and Ralph D. Freeman.
Group in Vision Science, School of Optometry, University of California,
Berkeley, CA 94720-2020.
APStracts 2:0334N, 1995.
SUMMARY AND CONCLUSIONS
1. Spatiotemporal receptive fields (RFs) for left and right eyes were studied
for simple cells in the cat's striate cortex to examine the idea that
stereoscopic depth information is encoded via structural differences of RFs
between the two eyes. Traditional models are based on neurons that possess
matched RF profiles for the two eyes. We propose a model that requires a
subset of simple cells with mismatched RF profiles for the two eyes in
addition to those with similar RF structure. 2. A reverse correlation
technique, which allows a rapid measurement of detailed RF profiles in the
joint space-time domains, was used to map RFs for isolated single neurons
recorded extracellularly in the anesthetized paralyzed cat. 3. Approximately
30% of our sample of cells shows substantial differences between spatial RF
structure for the two eyes. Nearly all of these neurons prefer orientations
between oblique and vertical, and are therefore presumed to be involved in
processing horizontal disparities. On the other hand, cells that prefer
orientations near horizontal have matched RF profiles for the two eyes.
Considered together, these findings suggest that the visual system takes
advantage of the orientation anisotropy of binocular disparities present in
the retinal images. 4. For some cells, the spatial structure of the RF changes
over the time course of the response (inseparable RF in the space-time
domain). In these cases, the change is similar for the two eyes, and therefore
the difference remains nearly constant at all times. Since the difference of
the RF structure between the two eyes is the critical determinant of a cell's
relative depth selectivity for the proposed model, space-time inseparability
of RFs is not an obstacle for consistent representation of stereoscopic
information. 5. RF parameters including amplitude, RF width, and optimal
spatial frequency are generally well matched for the two eyes over the time
course of the response. The preferred speed and direction of motion are also
well matched for the two eyes. These results suggest that the encoding of
motion-in-depth is not likely to be a function of simple cells in the striate
cortex. 6. The results presented here are consistent with our model in which
stereoscopic depth information is encoded via differences in the spatial
structure of RFs for the two eyes. This model provides a natural binocular
extension of the current notion of monocular spatial form encoding by a
population of simple cells. Note, however, that our findings do not exclude
the possibility that positional shifts of RFs also play a role in determining
the disparity selectivity of cortical neurons.
Received 14 April 1995; accepted in final form 30 October 1995.
APS Manuscript Number J252-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95