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Abstract:
Hubel and Wiesel (1962) proposed that complex cells in visual
cortex are driven by a pool of simple cells with the same preferred
orientation but different spatial phases. However, a wide variety
of experimental results over the past two decades have challenged
the pure hierarchical model, primarily by demonstrating that many
complex cells receive monosynaptic input from unoriented LGN cells,
or do not depend on simple cell input. We recently showed, using a
detailed biophysical model, that nonlinear interactions among
synaptic inputs to an excitable dendritic tree could provide the
nonlinear subunit computations underlying complex cell responses
(Mel, Ruderman, Archie 1997). Our present work extends this result
to the case of complex cell binocular disparity tuning, by
demonstrating it in an isolated model pyramidal cell (1) disparity
tuning at a resolution much finer than the the overall dimensions
of the cell's receptive field, and (2) systematically shifted
optimal disparity values for rivalrous pairs of light and dark
bars---both in good agreement with published reports (Ohzawa,
Deangelis, Freeman, 1997). Our results reemphasize the potential
importance of intradendritic computation for binocular visual
processing in particular, and for cortical neurophysiology in
general.
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