Only a few studies have acoustically examined how first language (L1) and second language (L2) speech develops once bilingual speakers return to their L1 environment after a prolonged stay in an L2 context, and not much is known about the long-term effects of L1 re-immersion on both languages in phonetic terms. In this study, we analyzed acoustic data from 17 Japanese–English returnee bilingual speakers collected over the course of five years of L1 re-immersion. We ask whether these speakers exhibit changes at the phonetic level in their two languages, and whether these changes pattern with L1 reversal and L2 attrition. An examination of voice onset time, vowel formants, and three rhythmic measures showed that speakers exhibited language-specific values for each of the features. However, apart from some shifts in the L1 Japanese vowel space, we did not observe consistent longitudinal changes in these phonetic features, meaning our acoustic data only partially align with L1 reversal and L2 attrition. Where our data do point in this direction, they complement earlier results from a global foreign-accent rating study with the same speakers, and align with other acoustic studies that looked at L1 reversal but over shorter time spans. Our data tentatively suggest that L1 speech reversal in this returnee population emerges relatively quickly and continues over time, while L2 speech attrition unfolds more gradually.
Laméris et al. (Sat,) studied this question.