Presentation
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High specificity of top-down modulation in the visual word form area
Poster A73 in Poster Session A, Thursday, October 6, 10:15 am - 12:00 pm EDT, Millennium Hall
Alex White1, Kendrick Kay2, Jason Yeatman3; 1Barnard College, Columbia University, 2University of Minnesota, 3Stanford University
Reading requires communication between visual cortex and language regions. The “visual word form area” (VWFA) in ventral occipito-temporal cortex is, like other areas that surround it, optimally driven by particular types of visual stimuli — in this case, written words. It is not completely selective for words, however, and it shows an intriguing pattern of top-down modulations. In this fMRI study we investigated the interaction of bottom-up visual factors and top-down cognitive factors in the VWFA. We presented participants with strings of letters and strings of visually similar shapes. We also manipulated the task demands: for each stimulus type participants did a task in which the stimuli were task-relevant and attended (lexical decision and gap localization, respectively), and a task in which the stimuli were irrelevant and ignored (a fixation color change task). We hypothesized that both stimulus types should evoke larger responses when attended than ignored, throughout visual cortex. The result was more complex: in the VWFA, letter strings evoked much larger responses when they were task-relevant than when they were irrelevant. However, non-letter shapes evoked smaller responses when they were task-relevant than when they were irrelevant. Activity in the VWFA was also correlated with a putative Broca’s area in the left pre-central sulcus, most strongly during the lexical task. These patterns of results were largely absent in all other visual areas. To conclude, we propose that communication between visual cortex and language regions is under voluntary control, and it selectively enhances the representation of written words in VWFA.
Topic Areas: Speech Motor Control, Control, Selection, and Executive Processes