Richard Born, M.D.
Harvard Medical School
will speak on
Reassembling the Visual World: The Integration of Motion Cues by
Cortical Neurons
Abstract:
A critical step in the interpretation of the visual world is the
integration of the various local motion signals generated by moving
objects. This process is complicated by the fact that local velocity
measurements can differ depending on contour orientation and spatial
position. Specifically, any local motion detector can measure only
the component of motion perpendicular to a contour that extends
beyond its field of view. This "aperture problem" is particularly
relevant to direction-selective neurons early in the visual pathways,
where small receptive fields permit only a limited view of a moving
object. I will describe experiments showing that neurons in the
middle temporal visual area (MT/V5) reveal a dynamic solution to the
aperture problem. MT neurons initially respond primarily to the
component of motion perpendicular to a contour's orientation, but
over a period of approximately 60 ms the responses gradually shift to
encode the true stimulus direction, regardless of orientation. I will
also describe a behavioral correlate of these neural responses: The
initial velocity of pursuit eye movements deviates in a direction
perpendicular to local contour orientation, suggesting that the
earliest neural responses influence the oculomotor response. This
behavior has afforded us the ability to probe a number of the
integrative properties of the visual motion system, including the
influence of cognitive factors.
The lecture will take place in
Room 401, 44 Cummington St.
on Friday, December 13, 2002
at 11:00 am
Hosted by the
Brain and Vision Research Laboratory