Phonemic category development in a teenage Mandarin-Japanese 2L1 bilingual: A longitudinal study with monolingual and 2L1 adult bilingual comparisons

Aims: This longitudinal case study examines phonemic category development in a Mandarin-Japanese 2L1 bilingual at 11;2 and 11;10. Methodology: The recordings for this study were collected when the participant was 11;2 and 11;10 years old, respectively. Each recording session comprised recordings in both Mandarin and Japanese, with a 4-day interval between the recordings for each language. Therefore, there were two recordings for each language condition. Data Analysis: For Mandarin and Japanese vowels, the focus was on F1 and F2. For stops, voice onset time (VOT) and onset F0 were analyzed. In addition, two Univariate General Linear Models examined whether VOT was a cue for stop differentiation in Mandarin, and two Multivariate General Linear Models assessed whether both VOT and onset F0 were cues for stop differentiation in Japanese. The results of this study were also compared with those from a previous study examining adult Japanese monolinguals and Mandarin-Japanese 2L1 adult bilinguals. Findings and Conclusions: The participant separated the vowels in the two languages more distinctly and adjusted the use of VOT and F0 as cues for Japanese stop differentiation from the first session to the second. This indicates a marked development in understanding the phonemic differences between Mandarin and Japanese, both in terms of vowels and stops. Compared to Mandarin-Japanese 2L1 adult bilinguals and adult Japanese monolinguals, the participant gradually aligns with Mandarin-Japanese 2L1 adult bilinguals’ phonemic patterns while diverging from adult Japanese monolinguals. Originality: This longitudinal study focuses on a teenage 2L1 bilingual, whereas most previous studies have concentrated on either young 2L1 bilingual children or adult 2L1 bilinguals. In addition, this study compares the teenage 2L1 bilingual with both adult monolinguals and adult 2L1 bilinguals, whereas most previous studies compare 2L1 bilingual children with either age-matched monolingual children or monolingual adults. Significance: This study reveals that significant phonemic adjustments and strategic refinements occur during the teenage years, suggesting that this period is possibly crucial for achieving efficient bilingual language management, although this may indicate some movement from monolingual patterns toward 2L1 adult bilingual patterns.