It is well known that second language (L2) learners have difficulties in acquiring speech sound contrasts not present in their native language. Some documented difficulties include the English /l/-/ɹ/ contrast for Japanese learners and the English /i/-/ɪ/ contrast for Spanish and Korean learners. This may be related to the observation that native listeners categorize speech sounds using multiple acoustic cues but that, for any given contrast, they pay more attention to certain cues over others; this is referred to as perceptual cue weighting.
Most studies of L2 acquisition of sound categories have focused either on comparing the learning of different contrasts or on the learning of appropriate cue weights for particular contrasts. Most studies have also used cross-sectional approaches to investigate the development of L2 speech acquisition. Moreover, relatively little has been reported on age-related differences in L2 speech acquisition. Taken together, this has limited our understanding of (1) how individuals’ cue weighting strategies change over time, (2) how cue weights are acquired across contrasts, (3) how developmental changes in perception are related to those in production within individual learners, (4) how L2 speech acquisition influences L1 categories over time, and (5) whether adult and child learners show different developmental patterns. The goal of this project is to address these issues using longitudinal data to better understand how individual second language learners differ in their developmental trajectories in the acquisition of novel speech sound contrasts over time.