Psychological and Brain Sciences Brown Bag Seminar: Alex White, University of Washington
Capacity Limits for Visual Word Recognition in Brain and Behavior
Alex White, Ph.D., Postdoctoral Research Associate, Department of Psychology, University of Washington
Abstract: Vision begins with parallel processing: the retinas encode many stimulus elements simultaneously, across the visual field. If parallel and independent processing continued all the way through the system, you would be able to read this abstract all at once. In the first part of my talk I will present behavioral evidence that, to the contrary, a fundamental processing bottleneck makes it impossible to recognize more than one word at a time. I will then present a neuroimaging study designed to identify the source of that bottleneck. The data show that early visual areas encode multiple words in parallel, and that neuronal responses to attended words are higher than to ignored words. Within the left hemisphere “visual word form area” (VWFA), a critical component of the reading circuitry, we find a hierarchy of sub-regions. A posterior portion of the VWFA can encode two words in separate spatial channels. The anterior portion of the VWFA has response properties consistent with a bottleneck. Therefore, although it is impossible to recognize two words at once, the visual system – including word-selective areas ¬ – processes both in parallel. The bottleneck lies at a relatively late stage in the ventral stream.