Integration of Motion and Stereopsis in Cortical Area MT of the Macaque
David C. Bradley, Ning Qian and Richard A. Andersen, Nature,
1995, 373:609-611.
Abstract
The primate visual system incorporates a highly specialized subsystem
for the analysis of motion in the visual field. A key element of this
subsystem is the middle temporal (MT) cortical area, which contains a
majority of direction-selective neurons. MT neurons are also
selective for binocular disparity (depth), which is perplexing given
that they are not sensitive to motion through depth. What is the role
of disparity in MT? Our data suggest an important link between
disparity and transparent motion perception. Motion signals in
different directions tend to inhibit each other within a given MT
receptive field. This inhibition has an averaging effect which
minimizes MT responses to random motion signals created by light
intensity changes and other non-motion stimuli (motion noise). But,
in the absence of disparity cues, inhibition may also occur between
surfaces moving in different directions through the same part of the
visual field (transparent motion), thus impairing the dectection of
either surface. Here we show that inhibition in MT occurs mainly
between motion signals with similar disparities. Transparent surface
movements at different depths are thus represented independently in MT
(that is, without inhibiting each other) whereas spurious motion signals
from a given surface tend to cancel out. To our knowledge, these
results provide the first evidence for a functional integration of
motion and disparity in MT.
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