Abstract
This study analyzes the production of native (L1) and foreign (L2) vowels by 42 L1 English learners of French (ELoF) at the start and end of a 6-month residence abroad (RA) in a French-speaking country. Data are also reported from a delayed post-test, which takes place 10 months after a subsection of participants (n = 27) return to the L1 English environment. Results reveal systemic phonetic drift in ELoF's L1 English vowels over the RA, and this accompanies the phonetic development occurring in the participants' L2 French vowel system, a phenomenon we label "tandem drift." This L1-L2 link is also supported by interspeaker variation: the individuals whose L2 French vowels shift the most are also the participants who exhibit the most substantial L1 phonetic drift in the same direction. Results for the L1 re-immersion time point suggest a partial-but not complete-reversal of phonetic drift, whereas no reversal of the L2 gains made over the RA is apparent. Nevertheless, at the individual level, the learners whose L2 gains reverse the most upon L1 re-immersion are also most likely to exhibit reverse phonetic drift in their L1. Overall, these findings indicate a relationship between L2 speech learning and L1 phonetic drift, which we argue is driven by the global phonetic properties of both L2 and L1 becoming linked at a representational level. Although these representations appear malleable, it is clear that recent changes are not guaranteed to reverse despite substantial re-exposure to L1 input. Implications for the distinction between drift and attrition are discussed.