Reading ability in both deaf and hearing adults is linked to neural representations of abstract phonology derived from visual speech

Learning to read provides access to life-long educational and vocational opportunities. Some, but not all, deaf children find learning to read challenging, due to reduced access to language, whether spoken or signed. In hearing children, the ability to access and manipulate well-specified, abstract ‘phonological representations’ of spoken language is important for developing strong reading skills. However, the role that phonology plays in deaf children learning to read is much less clear. Positive associations between speechreading (lip reading) and text reading have been observed in deaf and hearing children, and deaf adults, suggesting that speechreading may play a role in reading development, regardless of hearing status. Further support for this hypothesis would be provided by evidence that similar neural representations of phonology are evoked by visual speech and other language forms (auditory speech and text), and that these neural representations are related to reading proficiency. We used fMRI and Representational Similarity Analysis (RSA) to identify shared neural representations of phonology. A group of deaf adult participants (N=22), with a mixture of sign language and spoken language backgrounds and reading abilities, were presented with single lexical items as visual speech and text. Adult hearing participants (N=25) were presented with the same words, but as visual speech and auditory speech. We hypothesised that common neural representations of phonological structure of English words would be found in each group in the superior and middle temporal cortex (STC/MTC) and that these shared representations would be more similar across different language forms in better readers. Our data supported these predictions providing neurobiological evidence of the contribution of visual speech to abstract phonological representations, that relate to reading proficiency, in both deaf and hearing adults.