The Journal of Neuroscience, September 15, 2001, 21(18):7293-7302
Responses of Macaque V1 Neurons to Binocular Orientation
Differences
Holly
Bridge1 and
Bruce
G.
Cumming2
1 University Laboratory of Physiology, Oxford, OX1 3PT,
United Kingdom, and 2 Laboratory of Sensorimotor Research,
National Eye Institute, National Institutes of Health, Bethesda,
Maryland 20892-4435
Interocular differences in orientation occur during binocular
viewing of a surface slanted in depth. These orientation disparities could be exploited by the visual system to provide information about
surface slant, but gradients of positional disparity provide an equally
effective means to the same end. We examined the encoding of
orientation disparities in V1 neurons that were recorded from two awake
fixating monkeys. Monocular orientation selectivity was measured
separately in each eye. Although the preferred monocular orientation in
the left and right eyes was highly correlated (r = 0.98), 19 of 61 cells showed a significant interocular difference in
preferred orientation (IDPO). By itself, an IDPO does not imply a
specific binocular selectivity for orientation differences. We
therefore examined the response to 25 binocular combinations of
orientations by pairing each of five orientations in one eye with five
in the other. Forty-four of 64 neurons showed responses that reflected
the monocular orientation tuning selectivity; the preferred orientation
disparity changed when the monocular orientation was changed in either
eye. The remaining third (20 of 64) responded to a consistent
orientation disparity in a way that was not simply predictable from
monocular orientation selectivity. However, nearly all of these neurons
were selective for positional disparity, and several characteristics of
the responses suggest that the apparent selectivity for orientation
disparities was just a consequence of the positional disparity
sensitivity. Neither the data presented here nor previous data from the
cat (Blakemore et al., 1972; Nelson et al., 1977) support the idea that
a population of neurons early in the visual system has a separate
encoding scheme for orientation disparities.
Key words:
orientation disparity; positional disparity; energy
model; cortical area V1; awake macaque; electrophysiology
Copyright © 2001 Society for Neuroscience 0270-6474/01/21187293-10$05.00/0
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