Vision Research Discussion Group
Monday, October 4, 2004
Presented by the Vision Research Discussion Group
The Vision Research Discussion Group (VisioNYC) is a group of vision scientists from the Greater New York area, meeting at the Academy.
This seminar includes two short presentations from speakers outside the area, one on systems/computational aspects, and the other on cellular and molecular aspects of the normal and diseased visual systems.
Peter Sterling, University of Pennsylvania, "Psychophysics to Biophysics: Efficient Circuits from Stochastic Synapses."
Steven Yantis, Johns Hopkins University, "Visual Attention and Cognitive Control in the Human Brain."
8:00–9:00: Refreshments and informal discussions.
"Psychophysics to Biophysics: Efficient Circuits from Stochastic Synapses"
We detect a small, brief spot when the contrast is ~3%. This behavior depends on a single ganglion cell with the same sensitivity as the behavior, suggesting that information encoded in the ganglion spike train is transmitted to cognitive levels without loss. Within the retina, coding is also efficient, because circuits use many ribbon synapses that release vesicles at high rates. Loss of information occurs only when the ganglion cell converts its graded potential into spikes. Thus, although synapses operate chastically, the larger circuits achieve nearly perfect efficiency.
"Visual Attention and Cognitive Control in the Human Brain"
Selective attention is the cognitive mechanism that grants sensory input access to awareness and memory. We have investigated the time course of voluntary attentional control signals in human cortex using rapid event–related fMRI during tasks that require shifts of attention between locations, features, or objects, or between vision and audition. Within each domain, cortical activity in sensory regions is strongly modulated by attention. Furthermore, we observe both transient and sustained changes in activity in posterior paritetal and superior prefrontal cortex that are time locked to shifts of attention. These temporal profiles suggest a consistent role for these attentional control structures in the initiation and maintenance of new attentive states within multiple sensory domains.