L1 drift and L2 category formation in second language learning.

Assimilatory phonetic drift in L1 has been shown to occur in early second language learners when separate L2 categories have not been established. The direction and likelihood of drift is affected by degree of L1:L2 difference [2], and the need to maintain L1 distinctions [10]. We assessed the impact of explicit L2 phonetic training on L1:L2 interaction when novel L2 sounds could lead to a more crowded L1-L2 phonetic space. Native English-speaking college students completed a lesson on Spanish:English stop voicing contrasts midway through their first semester of introductory Spanish. Training led to improved Spanish VOT values, improved L1 and L2 category differentiation for most subjects, and L1 phonetic drift in voiceless and/or voiced stops for individual speakers. Thus, explicit instruction can facilitate L2 category learning even when this produces crowding among L1 and L2 categories. Furthermore, L1 drift is a common but not necessarily inevitable part of the process.