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Skilled deaf, but not hearing, readers exhibit neural tuning in the right Visual Word Form System
Poster Session C, Friday, October 25, 4:30 - 6:00 pm, Great Hall 3 and 4
Karen Emmorey1, Stephen McCullough1, Brennan Terhune-Cotter1, Laurie S. Glezer1; 1San Diego State University
Neuroimaging studies indicate that successful visual word recognition relies on a hierarchical organization in left ventral occipitotemporal cortex in which neurons are tuned along a posterior-to-anterior gradient to increasingly complex word features (e.g. from oriented bars, to letters, to bigrams, etc.). The hierarchical nature and neural selectivity of this region, termed the ‘visual word form system’ (VWFS), appears to be specific to the left hemisphere in hearing adult readers. In addition, both hearing and deaf skilled readers exhibit selectivity to whole words in an anterior location of the VWFS, termed the visual word form area (VWFA). However, unlike skilled hearing readers, skilled deaf readers also appear to engage the right VWFA. Although recruitment of the right hemisphere has been implicated in poor reading for hearing people, this does not appear to be the case for skilled deaf readers. For example, the N170 ERP response to printed words (likely generated by the VWFS) is bilateral for skilled deaf readers, and the amplitude of the right hemisphere N170 is positively correlated with reading and spelling ability for deaf readers, suggesting that recruitment of the right hemisphere is not maladaptive for these readers. We aimed to examine the hierarchical organization to written words in the VWFS bilaterally for skill-matched deaf and hearing readers to determine whether deafness (and phonological ability) modulates the laterality of word-selectivity gradients. Using fMRI, we employed the same design used in other studies of the VWFS, presenting stimuli that represented a scale of orthographic regularity: consonant strings, pseudowords, and real words. Participants performed a low-level task (detect a color change) that imposed a constant strategic processing load across all stimuli. Our results replicate previous findings showing a hierarchical structure solely in the left VWFS in skilled hearing readers. In skilled deaf readers, we find this same hierarchical structure in the left VWFS. As the deaf readers in this study had relatively limited knowledge of spoken phonology, this result shows that orthographic tuning in the VWFS is not altered by imprecise phonological representations. Importantly, we also find the same hierarchical structure in the right VWFS only for deaf readers. Unlike studies that show right hemisphere activation in people with dyslexia, the bilateral processing and tuning to written words seen here is not maladaptive since all participants were skilled readers. These results add critical information to our understanding of the neural architecture for reading. Our findings support the hypothesis that in hearing people, both the right and left VWFS are initially engaged in written word reading, but with strong phonological processing, successful reading development shifts to the left hemisphere. We show here that deaf skilled readers exhibit hierarchical organization bilaterally, which suggests a potential unique neural signature for reading in deaf adults. Moreover, the bilateral engagement of the VWFS in single word reading indicates that a shift to the left hemisphere does not need to transpire for successful reading to occur. Our study provides evidence for a strong role for spoken phonology in determining laterality for reading in hearing people.
Topic Areas: Reading, Signed Language and Gesture