Oxyopias 1997
December 5, 12:00 noon, 489 Minor Hall
Geoffrey Boynton
Department of Psychology, Stanford University
Host: Ben Backus
Linking Human Brain Activity with Psychophysical Performance using fMRI
Wed Dec 3, 4PM, room 489 Minor Hall
Yves Fregnac
University of Paris, C.N.R.S., France
Host: Ralph Freeman
Synaptic view of space and time in visual cortical neurons
Nov 14, 12:00 noon, 489 Minor Hall
Wayne Verdon
School of Optometry, UC Berkeley
Host: Gunilla Hagerstrom-Portnoy
Is the rod electroretinogram reduced in rod monochromatism?
Abstract
The ganzfeld electroretinogram (ERG) is a complex gross response to
flash stimulation of the retina. It is easily recorded in humans using a
non-invasive contact lens electrode. ERG waveforms have several
sub-components which are associated with the responses of different retinal
cell types.
The ERG is a standard clinical test to diagnose rod
monochromatism.Rod monochromats have few or no functional cones, but
supposedly normal rods. Therefore we expect an extinguished cone ERG and
normal rod ERG in rod monochromats. The extinguished cone ERG is found,
but clinical observation shows that the dark adapted ERG is reduced in
amplitude in rod monochromacy compared to that of the normal eye. This
finding has gone unexplained for decades.
There are several possible causes for the relative reduction in the
rod monochromat's dark adapted ERG response. Our investigation leads us to
look at the Lamb & Pugh phototransduction parameters, PII (bipolar cell)
responses, inner retinal contributions to the ERG (the oscillatory
potentials) and to re-examine the responses of dark adapted cones in the
normal eye.
We find that the rod PIII components of normal eyes and achromatic
eyes behave identically. In the normal eye we find a surprising difference
in the dark adapted versus light adapted cone response to moderate flash
energies, but that the difference is not present at high flash energies.
This new finding can account partially for the clinical observation. This
result has strong implications for the use of moderate flash energies (such
as recommended by the International Society of Clinical Electrophysiology
in Vision) in interpreting the ERG in disorders that affect cone function
more than rod.
Nov 7,12:00 noon,489 Minor Hall
Bart Anderson
Dept of Brain & Cognitive Science, MIT
The insufficiency of binocular disparity for understanding stereoscopic depth
October 31, 12:00 noon, 489 Minor Hall
Clay Radke
UC Berkeley, Chemical Engineering
Host: Ken Polse
Tear mixing under a soft lens: Measurement and model
Abstract
Clay Radke and Kenneth Polse
Soft contact lens extended lens wear (SCLEW) may lead to several corneal
complications, some of which can result in substantial vision loss. There
is considerable evidence that at least one factor contributing to adverse
corneal responses accompanying SCLEW is corneal hypoxia present during eye
closure. With the development of high oxygen transmissibility (Dk/L)
lenses, clinicians and investigators were optimistic that soft lenses could
be worn safely for overnight wear. Unfortunately, preliminary clinical
studies using high-Dk/L materials have shown that not all adverse corneal
responses have been eliminated, and therefore it seems that there are other
factors responsible for SCLEW keratopathies.
At least one additional factor that seems particularly important in
avoiding adverse ocular responses is adequate tear exchange during open-eye
wear following sleeping with the lens. With current SCLEW, clinicians have
observed that when subjects open their eyes after sleeping with lenses,
there is an accumulation of debris trapped at the tear-lens interface. For
some patients, once the eye is open, the debris may take several minutes to
several hours to be eliminated. A clue to the possible significance of
this trapped debris comes from studies of rigid-gas-permeable extended wear
(RGPEW) in which trapped debris is usually removed after only 1 or 2
blinks. With RGPEW many of the more worrisome complications accompanying
SCLEW (e.g., infection, infiltrative keratitis, etc.) are rarely observed.
Based on these findings, clinicians and investigators have suggested that
prolonged contact between trapped debris and the corneal epithelium may be
partly responsible for changes in epithelial physiology that accompany
extended wear (e.g., increased epithelial permeability, microcysts,
superficial keratitis, and bacterial adherence to epithelial cells).
We hypothesize that persistent trapped debris remaining under the contact
lens after overnight wear contributes to SCLEW keratopathies. To explore
this hypothesis a method to measure tear mixing under a contact lens and a
model that helps to define the factors controlling tear mixing are needed.
In this seminar, we report on a technique for measuring tear mixing and a
model that defines tear mixing under a contact lens. The technique for
estimating tear mixing uses fluorophotometry to measure the change in
concentration of a high MW (FITC-Dextran) compound under a soft contact
lens. Using fluorescein intensity data, we have developed a composite
exponential model to describe the exponential rate at which the dye flows
from the post-lens compartment, which provides an expression for tear
mixing under the lens.
The model described is based on the principle that fluid motion in the
post-lens tear film during blinking follows simple hydrodynamic lubrication
theory. Mixing due to this fluid flow is proposed to originate from
dispersion: a combination of diffusion normal to the moving lens and
parallel flow under the lens. The new dispersive mixing model displays an
exponential decay of tracer concentration and is in agreement with the
FITC-Dextran data obtained using the fluorophotometry technique. Thus the
dispersive mixing model can be used to explore the role of various lens
and ocular factors that affect tear flow under the lens. Ultimately the
model may be used to develop new materials and lens designs that will
provide improved tear flow under soft contact lenses.
October 17 ,12:00 noon,489 Minor Hall
Bruce Cumming
Host Ralph Freeman
The relationship between stereopis and neuronal activity in V1
Abstract:
There is considerable divergence in views about the role of V1 cortical
neurons in stereopsis. The analysis of much experimental work on disparity
selectivity uses simple local-filtering models based on the summation of
inputs from different locations on the two retinae. Others have asserted
that neurons in V1 play a central role in the solution of the binocular
correspondence problem. The incompatibility of these two views is
highlighted, and some experimental tests that distinguish them
unambiguously are discussed.
Recordings were made from single neurons in cortical area V1 of awake,
behaving primates. Both animals and humans were tested psychophysically on
the stereoscopic percepts elicited by the stimuli.
We presented local binocular matches inside the neuronal receptive field
that were inconsistent with the globally-perceived stereoscopic depth (as
reported perceptually). In one case, the individual bars of sinusoidal
stimuli presented within a sharply-defined circular window evoke responses
from disparity-selective cortical neurons. A configuration was used in
which the perceived disparity of the entire pattern was constrained by the
window to be different from the local disparity of the bars within the
receptive field. In another case, anti-correlated random-dot stereograms
were used to place binocularly consistent stimulation within the receptive
field of V1 cortical neurons. No depth is perceived with these
anti-correlated random-dot patterns. In both cases, the responses of V1
neurons was in accord with the local filtering model and not with the view
that these neurons are able to solve the binocular correspondence problem.
These experiments suggest that the responses of V1 neurons in the
awake, behaving primate are consistent with some of the simplest versions
of the local filtering models. Therefore, considerable processing beyond
area V1 is required to extract that signals that actually dominate the
perceptual experience of stereoscopic vision.
October 10, 12:00 Noon, 489 Minor Hall
Shinsuke Shimojo
Computational and Neural Systems, Division of Biology
California Institute of Technology, Pasadena, CA
Host: Cliff Schor
Attention, Time and Awareness in Vision
Abstract
I will demonstrate two visual motion illusions, both of which were
discovered recently in my psychophysics laboratory, and indicating an
intriguing relationship among attention, time and awareness in visual
perception. One is the "line motion" illusion, in which a line segment
which is physically presented simultaneously nonetheless appear to
unfold or extend from the attended portion to the unattended portion in
the visual field. The other is "spoke" illusion, in which increasing
rate of apparent motion stimuli leads to reversal of direction in
perceived motion due to the limited temporal resolution of visual
information processing. Variations of these basic illusions and
psychophysical data all together suggest that: (a)each of multiple
cortical representations/pathways has its own temporal efficiency or
capacity, (b)this efficiency, however, is modulated by factors such as
attention and complexity of stimuli, and (c)these temporal properties
could indeed be reflected in our conscious experience of visual motion.
September 26, 12:00 noon, 489 Minor Hall
Luciano da Fontoura Costa
Institute of Physics and Informatics, University of Sao Paulo, Brazil
Host Ralph Freeman
Neuromorphometry - Brief Review, New Techniques, and Perspectives
Abstract
The objectives of the current talk are: (i) to briefly
review the importance and state-of-the-art regarding the morphometric
analysis of neural cells (neuromorphometry); and (ii) to describe new
developments and perspectives in this incipient area. The techniques to
be presented and discussed include: fractal dimension, spatial coverage
and complexity measurements, convex hull, Hough transform, Fourier
transfomr, orientation histograms, entropy, multiscale characterization
through wavelets, multiscale bending energy, multiscale curvature, 3D
measures, fields, active contours, and automated generation of
dendrograms. Aspects regarding the classification of neural cells,
including some real case-examples, will also be briefly
discussed.
Friday, August 29, Noon Rm 489, Minor Hall
Mark Mon Williams
University of Queensland in Australia
Host: Dan Harvitt
A curious illusion suggests complex interactions in distance perception
Abstract
Binocular perception of the distance to, and between, point light
targetsdepends on vergence angle: increasing vergence angle decreases
apparent distance and vice versa. We tested whether this effect occurs in
more structured visual environments by manipulating vergence angle using an
ophthalmic prism. Placing a prism 'base-out' requires increased convergence
for target fixation; 'base-in' requires decreased convergence: the
triangulation account of distance perception predicts that apparent target
distance should decrease and increase respectively. The expected result was
not observed. Instead a consistent illusion of perceived distance was
obtained: egocentric target distance was judged to be significantly greater
regardless of prism orientation or target distance. We provide an
explanation for this phenomenon: the explanation is founded on the natural
responses of a perceptual system which reaches a self-consistent
representation of external 3-Dimensional space on the basis of mutually
interacting cues to distance. A model based on this idea allowed us to
predict modulations of the over-estimate with simple manipulations of the
viewing environment. Further experiments confirmed these predictions.
Friday, May 2, 12:00 noon, 489 Minor Hall
Greg DeAngelis
Department of Neurobiology, Stanford University School of Medicine, Stanford, CA
Host: Ralph Freeman
Processing of motion and depth in primate area MT
Friday, April 25, 12:00 noon, 489 Minor Hall
Charles Gray
University of California, Davis
Host: Ralph Freeman
Response synchronization in visual cortex: mechanisms and functions
Wednesday, April 23 ,11:00-12:00 , 101 Barker Hall
Dara Frank, PhD
Medical College of Wisconsin
UCB Visiting Miller Professor
School of Optometry/Department of Molecular & Cell Biology
Host: Suzanne Fleiszig
New insights into Pseudomonas aeruginosa pathogenesis
Friday, April 18, 12:00 noon, 489 Minor Hall
S.P. Srinivas
School of Optometry, UC Berkeley
Host: Joe Bonanno
Receptor mediated volume regulation in corneal endothelium
Friday, April 11, 12:00 noon, 489 Minor Hall
Bruno Olshausen
Center for Neuroscience, University of California, Davis, CA
Host: Ralph Freeman
Sparse coding with an over complete basis set: a strategy employed by V1?
Friday, April 4, 12:00 noon, 101 LSA
Gordon Fain
University of California, Los Angeles
Calcium constitutive activation and the mechanism of dark adaptation in photoreceptors
Monday, March 24, 4:00 PM, 489 Minor Hall
Fred Miles
National Institutes of Health, Bethesda, MD
Host: Cliff Schor
Short-latency eye movements as a probe for the early cortical processing of binocular visual signals
Friday, March 21, 12:00 noon, 489 Minor Hall
Gordon Legge
Dept. of Psychology
University of Minnesota, Minneapolis, MN
Mr. Chips: An ideal-observer model of reading
Friday, March 7, 12:00 noon, 101 LSA
Ken Miller
University of California, San Francisco
Orientation selectivity in primary visual cortex: development and mature circuitry
Friday, February 28, 12:00 noon, 101 LSA
Robert Desimone
National Institutes of Health
Bethesda, MD
Neural mechanisms for attention and memory in monkeys
Friday, February 14, 12:00 noon, 101 LSA
Frank Werblin
University of California, Berkeley
Morphological transformation in the retina
Friday, February 7, 12:00 noon, 489 Minor Hall
Erik Lumer
The Neurosciences Institute, San Diego, CA
Host: Ralph Freeman
Neural mechanisms of perceptual integration and rivalry during binocular vision: Insights from modeling studies
Friday, January 31, 2:00 noon, 489 Minor Hall
Al Seckel
California Institute of Technology, Pasadena, CA
Host: Martin Banks
You won't believe your eyes! What illusions reveal in brain and cognitive science
Friday, January 17, 4:00 PM, 489 Minor Hall
Bill Geisler
University of Texas, Austin, Texas
Host: Martin Banks
The role of primary visual cortex in pattern identification
Friday, January 10, 12:00 noon, 101 LSA
Robert Knight
Dept. of Neurology, School of Medicine, UC Davis
Attention mechanisms in humans
|
