Third-language learning affects bilinguals’ production in both their native languages: A longitudinal study of dynamic changes in L1, L2 and L3 vowel production

This study examined the impact of a study abroad (SA) English program on English and native vowel production. Basque-Spanish bilingual adolescents were assessed on their vowel production in English, Basque and Spanish before the SA program, the day after the program was completed, and four months later. The results revealed that after the SA program, participants’ English vowels were acoustically closer to English norms, revealing the effectiveness of SA programs in improving English vowel pronunciation. Yet, four months later, these benefits had faded, showing that regular input and active language use are required to maintain accurate pronunciation. SA also had effects on native production: bilingual participants showed assimilatory acoustic drift in both their languages towards the English vowel system; the extent of this drift was negatively correlated with improvements in English pronunciation. However, four months later, participants showed a ‘return’ drift towards their native norms. The results also revealed that usage frequency and switching habits played a ‘protective’ role: Frequent switching in bilinguals made the dominant native language less vulnerable to foreign-language influence. Our results suggest that factors related to the frequency and circumstances of native language use are key to authenticity in native language production