Developmental change in tone perception in Mandarin monolingual, English monolingual, and Mandarin-English bilingual infants: Divergences between monolingual and bilingual learners

Most languages use lexical tone to discriminate the meanings of words. There has been recent interest in tracking the development of tone categories during infancy. These studies have focused largely on monolingual infants learning either a tone language or a non-tone language. It remains to be seen how bilingual infants learning one tone language (e.g., Mandarin) and one non-tone language (e.g., English) discriminate tones. Here, we examined infants' discrimination of two Mandarin tones pairs: one salient and one subtle. Discrimination was investigated in three groups: Mandarin-English bilinguals, English monolinguals, and Mandarin monolinguals at 6 months and 9 months of age in a cross-sectional design. Results demonstrated relatively strong Mandarin tone discrimination in Mandarin monolinguals, with salient tone discrimination at 6 months and both salient and subtle tone discrimination at 9 months. English monolinguals discriminated neither contrast at 6 months but discriminated the salient contrast at 9 months. Surprisingly, there was no evidence for tone discrimination in Mandarin-English bilingual infants. In a second experiment, 12- and 13-month-old Mandarin-English bilingual and English monolingual infants were tested to determine whether bilinguals would demonstrate tone sensitivity at a later age. Results revealed a lack of tone sensitivity at 12 or 13 months in bilingual infants, yet English monolingual infants were sensitive to both salient and subtle Mandarin tone contrasts at 12 or 13 months. Our findings provide evidence for age-related convergence in Mandarin tone discrimination in English and Mandarin monolingual infants and for a distinct pattern of tone discrimination in bilingual infants. Theoretical implications for phonetic category acquisition are discussed.