University of California, San Diego
The Department of Psychology is Honored
to Present a Talk by
Geoff Boynton
Salk Institute
"Individual Differences in Acuity Predict Cortical Maps in Primary Visual and Somatosensory Cortex"
Presented on May 27, 2004
Location: The Crick Conference Room
Mandler Hall, room 3545
- Abstract:
- In the human primary visual cortex (V1), the cortical representation
of a foveal stimulus is much larger than in the periphery. This is
qualitatively consistent with visual acuity, which is much higher at
the center of gaze. To study this quantitatively, we compared visual
acuity thresholds in ten subjects with the topology of their primary
visual cortices, measured with fMRI. We found that subjects with
overall better visual acuity tend to have a larger primary visual
cortex, and subjects with the most rapid falloff in acuity with
eccentricity show a corresponding pattern in V1. A similar finding
was found in the somatosensory system, where cortical somatosensory
maps of the hand reflect individual differences in tactile acuity.
- About the Speaker:
- We are interested in the neural correlates of human visual perception. We
make use of a relatively new technique for measuring brain responses in
humans called Functional Magnetic Resonance Imaging or fMRI. This
technique uses a standard clinical MRI scanner to measure changes in the
blood flow and oxygenation of the vasculature in the brain that correlate
with neuronal responses. Our laboratory uses fMRI to determine where and
how the brain responds by making fMRI measurements in the visual cortex of
human observers while they view various visual stimuli.
Some of my previous work as a postdoctoral fellow at Stanford University involved studying brain responses in people with developmental dyslexia. We found that those with developmental dyslexia showed lower fMRI responses than control subjects in a motion processing area of the brain, called area MT+, and that these differences correlate well with behavioral measurements using a speed discrimination task. These results are consistent with the hypothesis that developmental dyslexia is associated with a deficit in the magnocellular pathway of the visual system.
Our current research includes studying the effects of spatial and feature-based attention on responses in early visual areas. Until recently, it was believed that the first stages of visual processing (in humans and other primates) operate in a passive, feed-forward manner that is independent of the attentional state of the observer. However, using fMRI, we discovered that directing both spatial and feature-based attention to specific parts of the visual field can modulate responses as early as in the primary visual cortex. This discovery requires us to think differently about the nature of the neural circuitry in the early stages of human vision.
For More Information About This Speaker:
- http://www.snl-b.salk.edu/
Dr. Boynton's lab webpage.
- http://www.snl-b.salk.edu/boynton/fMRI-mpegs.html
fMRI mpeg movies.
