Segmental acquisition in adult ESL learners: A longitudinal study of vowel production

Research on second language (L2) phonetic learning indicates that, even in adults, segmental acquisition remains possible through L2 experience. However, the findings of previous cross-sectional studies of vowel and consonant learning have proved difficult to interpret. In this longitudinal investigation of 44 recent arrivals in Canada, productions of 10 English vowels in CVC context were elicited at 2-month intervals and evaluated by trained and untrained listeners. Improved intelligibility was observed, even in the absence of focused instruction on vowels. The results support the proposal that L2 phonetic learning is initially rapid but tends to plateau within a few months. However, this finding is complicated by different learning trajectories across vowels, differential L1 influences, and possible effects of word frequency.