Binocular receptive field models,
disparity tuning, and characteristic disparity
Yudong Zhu and Ning Qian, Neural Computation, 1996, 8:1611-1641
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Abstract
Disparity tuning of visual cells in the brain depends on the structure
of their binocular receptive fields (RFs). Freeman and coworkers have
found that binocular RFs of a typical simple cell can be
quantitatively described by two Gabor functions with the same Gaussian
envelope but different phase parameters in the sinusoidal modulations
\cite{Freeman90}. This phase-parameter based RF description, however,
has recently been questioned by
\citeasnoun{Wagner93} based on their identification of a
so-called characteristic disparity (CD) in some cells' disparity
tuning curves. They concluded that their data favor the traditional
binocular RF model which assumes an overall positional shift between a
cell's left and right RFs. Here we set to resolve this issue by
studying the dependence of cells' disparity tuning on their
underlying RF structures through mathematical analyses and computer
simulations. We model the disparity tuning curves in Wagner and
Frost's experiments and demonstrate that the mere existence of
approximate CDs in real cells cannot be used to distinguish the
phase-parameter based RF description from the traditional
position-shift based RF description. Specifically, we found that
model simple cells with either type of RF description do not have a
CD. Model complex cells with the position-shift based RF description
have a precise CD, and those with the phase-parameter based RF
description have an approximate CD. We also suggest methods for
correctly distinguishing the two types of RF descriptions. A hybrid
of the two RF models may be required to fit the behavior of some real
cells and we show how to determine the relative contributions of the
two RF models.
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