James W. Pennebaker, Chair The University of Texas at Austin, SEA 4.212, Austin, TX 78712 • (512) 475-7596
"Imaging the dynamics of disparity encoding and disparity-based decision-making in human visual cortex"
Mon, December 3, 2012 • 12:00 PM - 1:00 PM • SEA 4.244
Anthony M. Norcia, Ph.D.
Department of Psychology
Reception with Refreshments at 11:30 AM
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Abstract: Our two side-by-side eyes view the world from different vantage points, creating slightly different retinal images. These retinal image "disparities" comprise an important cue for depth. How this cue is extracted and used to guide perceptual judgments about depth has been the subject intense research ever since the invention of the stereoscope by Wheatstone in 1838. The invention of the random-dot stereogram (RDS) by Julesz in the 1960's opened the modern era of research on stereopsis - the RDS allows one to present the disparity cue in isolation from all other cues for depth. By combining the cue-isolation of the RDS with MRI, fMRI and high-density EEG recordings, we can now visualize the unfolding of human stereo processing over time and cortical area with unprecedented fidelity. Using these methods, we find that disparity is encoded in a progressively richer fashion as one moves from early visual areas to second-tier extra-striate cortex including hV3A and Lateral Occipital cortex where a spatially antagonistic center-surround organization emerges. To study the transition from stimulus-related to response related activity, we have analyzed responses that are time-locking to the behavioral response in a speeded disparity discrimination task. Using this method, we find that hV4 is the earliest area whose variability is correlated with the behavioral reaction time.