RESUMEN
We examined the impact of exposure to a signed language (American Sign Language, or ASL) at different ages on the neural systems that support spoken language phonemic discrimination in deaf individuals with cochlear implants (CIs). Deaf CI users (N = 18, age = 18-24 yrs) who were exposed to a signed language at different ages and hearing individuals (N = 18, age = 18-21 yrs) completed a phonemic discrimination task in a spoken native (English) and non-native (Hindi) language while undergoing functional near-infrared spectroscopy neuroimaging. Behaviorally, deaf CI users who received a CI early versus later in life showed better English phonemic discrimination, albeit phonemic discrimination was poor relative to hearing individuals. Importantly, the age of exposure to ASL was not related to phonemic discrimination. Neurally, early-life language exposure, irrespective of modality, was associated with greater neural activation of left-hemisphere language areas critically involved in phonological processing during the phonemic discrimination task in deaf CI users. In particular, early exposure to ASL was associated with increased activation in the left hemisphere's classic language regions for native versus non-native language phonemic contrasts for deaf CI users who received a CI later in life. For deaf CI users who received a CI early in life, the age of exposure to ASL was not related to neural activation during phonemic discrimination. Together, the findings suggest that early signed language exposure does not negatively impact spoken language processing in deaf CI users, but may instead potentially offset the negative effects of language deprivation that deaf children without any signed language exposure experience prior to implantation. This empirical evidence aligns with and lends support to recent perspectives regarding the impact of ASL exposure in the context of CI usage.
RESUMEN
This study aimed to investigate the development of audiovisual speech perception in monolingual Uzbek-speaking and bilingual Uzbek-Russian-speaking children, focusing on the impact of language experience on audiovisual speech perception and the role of visual phonetic (i.e., mouth movements corresponding to phonetic/lexical information) and temporal (i.e., timing of speech signals) cues. A total of 321 children aged 4 to 10 years in Tashkent, Uzbekistan, discriminated /ba/ and /da/ syllables across three conditions: auditory-only, audiovisual phonetic (i.e., sound accompanied by mouth movements), and audiovisual temporal (i.e., sound onset/offset accompanied by mouth opening/closing). Effects of modality (audiovisual phonetic, audiovisual temporal, or audio-only cues), age, group (monolingual or bilingual), and their interactions were tested using a Bayesian regression model. Overall, older participants performed better than younger participants. Participants performed better in the audiovisual phonetic modality compared with the auditory modality. However, no significant difference between monolingual and bilingual children was observed across all modalities. This finding stands in contrast to earlier studies. We attribute the contrasting findings of our study and the existing literature to the cross-linguistic similarity of the language pairs involved. When the languages spoken by bilinguals exhibit substantial linguistic similarity, there may be an increased necessity to disambiguate speech signals, leading to a greater reliance on audiovisual cues. The limited phonological similarity between Uzbek and Russian might have minimized bilinguals' need to rely on visual speech cues, contributing to the lack of group differences in our study.