Bilateral Word Selectivity Gradients in the Visual Word Form System in Skilled Deaf Readers.

Abstract

In hearing people visual word recognition relies on a hierarchical organization in left ventral occipitotemporal (vOT) cortex. While right hemisphere recruitment has been implicated in poor reading, this may not be the case for deaf readers as there is evidence that for skilled deaf readers the right vOT is also engaged during word recognition. However, the nature of representations along the vOT hierarchy and the degree of laterality in skilled deaf readers remain largely unknown. This study aimed to examine the hierarchical organization for written words in the vOT 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 as previous studies, presenting stimuli that represent a scale of orthographic regularity: consonant strings, pseudowords, and real words. For hearing readers, our results replicate previous findings showing a hierarchical structure solely in the left visual word form system (VWFS). For deaf readers, we find this same hierarchical structure in the left VWFS, but we also observe a similar hierarchical structure in the right VWFS. Unlike studies that show maladaptive right hemisphere activation in people with dyslexia, the bilateral tuning to written words seen in our study is not maladaptive since all participants were skilled readers. The bilateral hierarchical organization of the VWFS represents a unique neural signature for successful reading in deaf adults and suggests that the typical developmental shift from bilateral to predominantly left-lateralized processing is not necessary for successful reading.