My laboratory
studies cortical circuits that mediate visual perception
and visually guided behavior. This work involves a
creative fusion of the disciplines of neurophysiology and
psychology. Monkeys are trained to perform demanding
visual discrimination tasks, and we record from single or
multiple neurons in visual cortex during performance of
these tasks. Thus, we can directly compare the ability of
neurons to discriminate between different visual stimuli
with the ability of the behaving animal to make the same
discrimination. In addition, the techniques of electrical
microstimulation and/or reversible inactivation are used
to establish causal links between physiology and
behavior.
Our research currently has two main foci: 1) Mechanisms
of stereoscopic depth perception. The image formed on
each retina is a two-dimensional projection of the
three-dimensional (3D) world. However, objects at
different depths project onto slightly disparate points
on the two retinas. The brain is able to extract these
binocular disparities from the retinal images and create
a vivid sensation of depth, such as when one views a
3D-art poster. My lab studies the mechanisms by which
binocular disparity information is encoded, processed,
and read out by the brain in order to perceive depth and
compute 3D surface structure. We are just beginning to
elucidate the brain areas that contribute to stereoscopic
depth perception under different conditions, and much
remains to be learned about this interesting cognitive
process. 2) Mechanisms of visual feature integration. At
early stages in the visual system, local visual features
(i.e., oriented line segments) are encoded by neurons
with very small receptive fields. How are these local
features assembled into complex representations of 3D
objects? One interesting and controversial hypothesis is
that feature integration occurs through temporal coding;
two neurons selective for local image features are
hypothesized to synchronize their activities when these
two units respond to parts of a single object, but not
when they respond to parts of different objects. Our work
is aimed at conducting rigorous tests of hypotheses such
as this. We train monkeys to perform visual
discrimination tasks that require feature integration,
and we record from multiple neurons in visual cortex
during the task.
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