How does literacy affect speech processing? Not by enhancing cortical responses to speech, but by promoting connectivity of acoustic-phonetic and graphomotor cortices

Previous research suggest that literacy, specifically learning alphabetic letter-to-phoneme mappings, modifies online speech processing, and enhances brain responses to speech in auditory areas associated with phonological processing (Dehaene et al., 2010). However, alphabets are not the only orthographic systems in use in the world, and hundreds of millions of individuals speak languages that are not written using alphabets. In order to make claims that literacy per se has broad and general consequences for brain responses to speech, one must seek confirmatory evidence from non-alphabetic literacy. To this end, we conducted a longitudinal fMRI study in India probing the effect of literacy in Devanagari, an abubgida, on functional connectivity and cerebral responses to speech in 91 variously literate Hindi-speaking individuals. Twenty-two completely illiterate participants underwent six months of reading and writing training. Devanagari literacy increases functional connectivity between acoustic-phonetic and graphomotor brain areas, but we find no evidence that literacy changes the way speech is processed, either in cross-sectional or longitudinal analyses. These findings shows that a radical reconfiguration of the neurofunctional substrates of online speech processing is not a universal result of learning to read, and raise the possibility that writing, not only reading, may be instrumental in moulding literate speech perception.