Impact of exposure to a signed language on spoken phonemic discrimination in adult CI users: A functional near-infrared spectroscopy study

We examined neural activation patterns underlying phonemic discrimination in a spoken language in deaf CI users (N=18, age=18-24 years) who were exposed to a signed language at different ages and in hearing individuals (N=18, age=18-21 years). In deaf CI users, early-life language exposure, irrespective of modality, was associated with greater neural activation of language areas that are critically involved in phonological processing. For deaf CI users with later age of implantation, early age of exposure to a signed language was associated with increased activation in the left hemisphere’s classic language regions for native language (English) versus non-native language (Hindi) phonemic contrasts. For deaf CI users with earlier age of implantation, no significant change related to the age of exposure to a signed language was observed. These findings lend support to the hypothesis that early sign exposure does not negatively impact language processing in a spoken language in deaf CI users but may potentially offset the negative effects of language deprivation that children without any sign language exposure experience prior to implantation.