Encoding of Binocular Disparity by Complex Cells in the Cat's Visual
Cortex.
Izumi Ohzawa, Gregory C. DeAngelis and Ralph D. Freeman.
Group in Vision Science, School of Optometry, University of California,
Berkeley, California 94720-2020.
APStracts 4:0062N, 1997.
ABSTRACT
To examine the roles that complex cells play in stereopsis, we have recorded
extracellularly from isolated single neurons in the striate cortex of
anesthetized paralyzed cats. We measured binocular responses of complex cells
using a comprehensive stimulus set that encompasses all possible combinations
of positions over the receptive fields for the two eyes. For a given position
combination, stimulus contrast could be the same for the two eyes (two bright
or two dark bars) or opposite (one bright and one dark). These measurements
provide a binocular receptive field (RF) profile that completely characterizes
complex cell responses in a joint domain of left and right stimulus positions.
Complex cells typically exhibit a strong selectivity for binocular disparity,
but are only broadly selective for stimulus position. For most cells,
selectivity for disparity is more than twice as narrow as that for position.
These characteristics are highly desirable if we assume that a disparity
sensor should exhibit position invariance while encoding small changes in
stimulus depth. Complex cells have nearly identical binocular RFs for bright
and dark stimuli as long as the sign of stimulus contrast is the same for the
two eyes. When stimulus contrast is opposite, the binocular RF is also
inverted such that excitatory subregions become suppressive. We have developed
a disparity energy model that accounts for the behavior of disparity-sensitive
complex cells. This is a hierarchical model that incorporates specific
constraints on the selection of simple cells from which a complex cell
receives input. Experimental data are used to quantitatively examine
predictions of the model. Responses of complex cells generally agree well with
predictions of the disparity energy model. However, various types of
deviations from the predictions are also found, including a highly elongated
excitatory region beyond that supported by a single energy mechanism.
Complex cells in the visual cortex appear to provide a next level of
abstraction in encoding information for stereopsis based on the activity of a
group of simple-type subunits. In addition to exhibiting narrow disparity
tuning and position invariance, these cells seem to provide a partial solution
to the stereo correspondence problem that arises in complex natural scenes.
Based on their binocular response properties, these cells provide a
substantial reduction in the complexity of the correspondence problem.
Received 7 November 1996; accepted in final form 4 February 1997.
APS Manuscript Number J877-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 20 February 1997