Dissociating phonological tuning from reading skill: Evidence from the temporoparietal cortex in deaf and hearing adults

Abstract

Phonological processing is widely considered central to reading development in hearing individuals, with the temporoparietal cortex (TPC) regarded as essential for encoding phonological information from print. Hearing people who struggle to read show altered activation and less precise phonological representations in this region. Notably, skilled deaf readers show this same profile, suggesting that precise phonological representations in the TPC are not necessary for proficient reading. This raises the question of what the TPC encodes when phonological access differs. Using fMRI, we compared skilled deaf and hearing readers viewing real words (RWs), pseudowords (PWs), and pseudohomophones (PHs)—letter strings that are orthographically novel but phonologically identical to real words (e.g., brane). Because PHs carry no lexical or semantic identity, they can isolate whole word phonological representations accessed through print. We examined BOLD signal differences within individually localized TPC ROIs. Deaf and hearing readers showed distinct response patterns. Hearing readers showed equivalent responses to PHs and RWs, both greater than PWs ((RW = PH) < PW), indicating that lexical-level phonological representations were accessed from print. Deaf readers showed the largest response to RWs and equivalent responses to PHs and PWs (RW < (PH = PW)), indicating that whole-word phonological forms were not reliably accessed from print. These findings suggest that in skilled deaf readers phonological information from print is encoded with reduced precision and/or less automatically, supporting the proposal that deaf readers achieve literacy through a potentially unique reading architecture where the direct orthographic-to-semantic pathway carries the primary functional load.