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Hoover:
Please post the attached ad on CVNet.
Thank you,
Barb Arnold
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POSTDOCTORAL POSITIONS AVAILABLE
CENTER FOR VISUAL SCIENCE
UNIVERSITY OF ROCHESTER
Training in Visual Science with emphasis on approaches that link visual
performance to underlying neural mechanisms: cortical mechanisms of
perception (Charles J. Duffy, Associate Professor, Neurobiology and
Anatomy, Neurology, Ophthalmology, Brain & Cognitive Sciences and Center
for Visual Science and Robert C. Emerson, Research Associate Professor of
Ophthalmology and Center for Visual Science).
Duffy currently has active projects on the neurophysiology and
psychophysics of optic flow field analysis for visuospatial orientation.
Two neurophysiology laboratories are engaged in single neuron recording
from cerebral cortex of awake monkeys. One laboratory is for single neuron
recording in awake monkeys that are trained to fixate on large screen optic
flow simulations of the visual motion seen in observer self-movement. The
second laboratory uses similar single neuron and visual stimulation
techniques combined with large-scale translational movement of the animal
in the room to provide both visual and non-visual cues about self-movement.
The psychophysics laboratory is devoted to studies of visual motion
processing in aging and dementia. In this laboratory human subjects stand
on a force platform for the recording of postural responses to optic flow
stimuli. Subjects can also be seated to view extensive series of optic
flow fields designed to quantify visual motion processing capacity relevant
to spatial orientation. Current interests: Visual-vestibular interactions
in cortical area MST of monkeys, MST neuronal responses to optic flow and
object motion stimuli, MST neuronal responses to optic flow in pursuit eye
movements, the impact of optic flow on hemispatial neglect after stroke,
and visual motion processing in aging and Alzheimer's disease.
Emerson uses nonlinear systems analysis with customized random
spatiotemporal stimuli (white noise) to study processes in the brain that
are necessary for perception of moving objects, and for maintaining a
linear range of contrast coding over the extensive range of contrast found
in the visual world. He clarified the spatial and temporal mechanisms of
motion selectivity in single complex neurons of the cat's striate cortex by
providing the first direct demonstration of the dependence of velocity
selectivity on inseparable nonlinear interactions in space and time. This
mechanism accomplishes the same smoothness of response that we associate
with the perception of a moving object, independent of its spatial and
textural properties. Modeling has shown that the smoothness is likely to
depend on a single neuron computing a phase-independent motion-energy
signal by using quadrature-phase filters followed by soft thresholds. This
nonlinear property is computed in multiple subunits across the receptive
field of a motion-selective neuron. More recently, Emerson has refuted the
purely linear view of simple cells by demonstrating that simple cells use
similar nonlinear subunits to achieve directional selectivity. They
linearize a simple cell's representation of a moving object by lowering the
normally high (nonlinear) threshold that all cortical neurons show, thus
preserving phase-sensitive signals for the preferred direction of motion.
Currently, Emerson is studying differences in preferred velocity between
the two eyes that would suggest neural selectivity for motion in depth.
Elemental motion responses from randomized haploscopic stimuli are
reassembled to predict a complete array of motion-in-depth responses that
could not be measured directly because of time limitations. Similar
measurements, after changing the contrast of the stimulus, will demonstrate
mechanisms of changes in gain and in temporal properties that allow the
visual system to operate efficiently over the wide range of contrasts that
occur in the visual environment.
Support is provided by the Training Grant funded by the National Eye Institute.
ELIGIBILITY: Ph.D, MD, or OD. US citizenship or permanent residency is
required.
MORE INFORMATION ABOUT THE CENTER AND FACULTY: http://www.cvs.rochester.edu/.
FOR FURTHER DETAILS CONTACT:
Barbara Arnold
barba@cvs.rochester.edu
Center for Visual Science
University of Rochester
Rochester, NY 14627-0270
716-275-8659 Fax: 716-271-3043
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Barbara Arnold email: barba@cvs.rochester.edu
Center for Visual Science phone: 716 275 8659
Room 274 Meliora Hall fax: 716 271 3043
University of Rochester
Rochester NY 14627-0270
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