Bimodal bilingualism as multisensory training?: Evidence for improved audiovisual speech perception after sign language exposure

• We investigated brain activation to audiovisual stimuli before and after sign exposure.
• Increased behavioral accuracy in audiovisual categorization after sign exposure.
• Greater activation in SMG and anterior insula after sign exposure.
• Mouthing-lipreading scores correlated with increased L-SMG activation.

The aim of the present study was to characterize effects of learning a sign language on the processing of a spoken language. Specifically, audiovisual phoneme comprehension was assessed before and after 13 weeks of sign language exposure. L2 ASL learners performed this task in the fMRI scanner. Results indicated that L2 American Sign Language (ASL) learners’ behavioral classification of the speech sounds improved with time compared to hearing nonsigners. Results indicated increased activation in the supramarginal gyrus (SMG) after sign language exposure, which suggests concomitant increased phonological processing of speech. A multiple regression analysis indicated that learner’s rating on co-sign speech use and lipreading ability was correlated with SMG activation. This pattern of results indicates that the increased use of mouthing and possibly lipreading during sign language acquisition may concurrently improve audiovisual speech processing in budding hearing bimodal bilinguals.