Monolingual, Non-tone Bilingual, and Tone Bilingual Infants: Language Experiences Alter Speech and Nonspeech Perception.

Studies on first-year infants' pitch perception have witnessed shifts of perceptual focus from acoustic to linguistic information and from a wide range of contrasts to those relevant to their native language. Nevertheless, how linguistic experience interacts with this developmental process remains an open question. This study compared the neural discrimination of speech/lexical and nonspeech/violin tone contrasts by 5- to 6- and 11- to 12-month-old infants across three types of language backgrounds: monolingual infants learning a non-tone language (Mono), bilingual infants learning two non-tone languages (Bi-NT), and bilingual infants learning a non-tone and a tone language (Bi-Tone). Although Mono infants do not show significant responses to the lexical tone contrast, both Bi-NT and Bi-Tone infants showed positive mismatch responses at both ages, indicating an enhancement effect brought by a complex language environment as early as 5 months after birth. Regarding the violin tone perception, distinct patterns were observed across language backgrounds: a perceptual decrease for Mono infants, no significant response for Bi-NT infants, and a perceptual increase for Bi-Tone infants over the first year. These patterns suggest that pitch perception may be affected across domains by language experiences at this stage, where interactions in cognitive processing between speech and nonspeech prosodic information may occur.