Tracking L2 English Vowel Perception and Production Among Graduate Professionals Over 18 Months.

This study investigates changes in English vowel perception and production among 22 advanced-proficiency second-language (L2) learners from diverse first-language (L1) backgrounds over 18 months at a large U.S. university, with a particular focus on the influence of the L2 English-speaking environment and the impact of the COVID-19 pandemic. The study employed Bayesian mixed-effects models to analyze participants' vowel identification accuracy using a perception oddity task and vowel production (intelligibility) accuracy using listener-based ratings at 1, 3, 6, and 18 months after arrival. The sudden shift to online instruction due to the COVID-19 pandemic, which occurred between Months 6 and 18, and the subsequent return of some participants to their home countries added an additional layer of complexity to the investigation. The findings revealed that the participants demonstrated high initial accuracy in identifying L2 vowels, with improvement observed for most contrasts over the first 6 months. Vowel intelligibility, in contrast, did not improve much, with only one contrast showing increased accuracy at the last data point. Individual trajectories showed variability in both perception and production, emphasizing the unique change trajectories of advanced-proficiency learners.