The deaf utilize phonological representations in visually presented verbal memory tasks

The phonological abilities of congenitally deaf individuals are inferior to those of people who can hear. However, deaf individuals can acquire spoken languages by utilizing orthography and lip-reading. The present study used functional magnetic resonance imaging (fMRI) to show that deaf individuals utilize phonological representations via a mnemonic process. We compared the brain activation of deaf and hearing participants while they memorized serially visually presented Japanese kana letters (Kana), finger alphabets (Finger), and Arabic letters (Arabic). Hearing participants did not know which finger alphabets corresponded to which language sounds, whereas deaf participants did. All of the participants understood the correspondence between Kana and their language sounds. None of the participants knew the correspondence between Arabic and their language sounds, so this condition was used as a baseline. We found that the left superior temporal gyrus (STG) was activated by phonological representations in the deaf group when memorizing both Kana and Finger. Additionaly, the brain areas associated with phonological representations for Finger in the deaf group were the same as the areas for Kana in the hearing group. Overall, despite the fact that they are superior in visual information processing, deaf individuals utilize phonological rather than visual representations in visually presented verbal memory.