Phonetic Discrimination in the First and Second Half-year of Life: An Investigation of Monolingual and Bilingual Infants using Event-Related Functional Near-infrared Spectroscopy (fNIRS)

How do infants learn the sounds of their native language? Do they need to use general-auditory or language-specific mechanisms to make sense of the distributional nature of their phonetic input? To answer this question, this study investigated the neural correlates of phonetic discrimination in monolingual and bilingual infants (2-6 and 10-14 months) and adults using a new lens afforded by functional Near-Infrared Spectroscopy (fNIRS) neuroimaging. All participants heard syllables phonetically contrastive in their native English and Hindi (non-native) in an oddball paradigm while being imaged with fNIRS. Age comparisons of infant brain activation in multiple sites revealed that left Broca‟s area showed a developmental decline in response to native-language experience only. Bilateral STG showed robust recruitment at both ages in response to both stimulus languages. These findings were robust across monolinguals and bilinguals. Together, the results suggest that all infants use neural tissue predisposed for linguistic-phonetic processing in early life.MAS