The reading brain: characterize the distinctiveness and functional specificity of the visual word form area
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Date
2023-02
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Abstract
The visual word form area (VWFA) is an experience-dependent region in the left ventral temporal cortex (VTC) that responds to written words and letters. However, after more than three decades of investigation, the nature and even the existence of this region is still under debate. Some studies suggest that the VWFA is not dedicated to visual words/not distinct from other VTC regions; others argue that the VWFA is not even visual and is instead part of the amodal language and/or attention networks. But without a clear definition of the VWFA and its VTC neighbors, and a without direct comparison of high-level visual, linguistic, or attentional neural responses in these regions, these debates still linger, preventing progress in the field. Here, we scanned 63 adults on: visual localizers to delineate subject-specific VTC category-selective fROIs; an auditory language localizer to assess linguistic processing within VTC vs. amodal/canonical frontotemporal language fROIs; and spatial working memory (SWM) task to assess attentional load-based responses. We found that only the VWFA shows a significantly greater response to visual words compared to all other high-level visual stimuli, auditory language conditions, and SWM conditions. Moreover, while the VWFA is unique within the VTC in showing word-selectivity, its selectivity to auditory language is on par with various other VTC fROIs. Further, any language selectivity within the VTC is dwarfed by visual selectivity even to non-preferred stimulus categories of the fROI, suggesting that the VTC is not part of the key language network. Additionally, all VTC fROIs, except RSC, were modulated by attention on the SWM task. Overall, we used precision fMRI with multiple tasks to thoroughly examine the response properties of the VWFA, finding that while it does show some linguistic and attentional sensitivities, it is clearly a visual region and distinct from adjacent VTC visual regions only in its neural preferences for orthography; it is also distinct from canonical language or dorsal attention networks, caring more about visual aspects of words than higher-level linguistic content. We propose that the role of the VWFA is more akin to a visual look-up dictionary of letters and words to facilitate perceptual processing, and that this percept is transferred to the canonical language network for high-level linguistic processing. We hope that the field can now move forward to addressing other interesting questions, including the origins and mechanisms of this region and more importantly, how human brains enable complex human cognition.
Description
Biological Sciences: 2nd Place (The Ohio State University Edward F. Hayes Advanced Research Forum)
Keywords
reading, visual word form area, neuroimaging, fMRI, high-level vision