The acquisition of new vowel contrasts by Korean learners of English: A longitudinal study


Most studies of second language (L2) learning of sound categories have focused on either comparing learning of different contrasts (Flege, 1995) or learning of appropriate cue weights to particular contrasts (Escudero et al., 2009), using cross-sectional approaches. This has limited our ability to understand (1) how individuals’ cue weighting strategies change over time and (2) how cue weights are learned across contrasts, especially between easier and harder contrasts that rely on the same acoustic cues. This study addresses both of these issues by examining the developmental changes in perceptual cue weighting of two English front vowel contrasts by Korean learners of English during their first 8 months of immersion in Canada. Twenty six native Korean listeners (12 adults & 14 children) participated in cue weighting experiments upon their arrival in Canada (Time 1). They were tested on their perceptual weighting again approximately 4 (Time 2) and 8 months (Time 3) later. Stimuli were resynthesized speech continua (Kawahara et al., 2008) based on natural recordings of the endpoints of both /bɪt/-/bit/ and /bɛt/-/bæt/ contrasts produced by a male native Canadian English speaker. Five steps varying in formant frequency were crossed with 5 duration steps and presented in a two alternative forced-choice identification task. We found that adult learners had an initial advantage in L2 speech acquisition over children at least for the /i/-/ɪ/ contrast, but after 8 months the children had significantly improved. Both groups of Korean learners showed differential acquisition patterns between the two English vowel contrasts; that is, they used both spectral and duration cues to distinguish /i/-/ɪ/ but only duration to distinguish /ɛ/-/æ/, suggesting that they had more difficulty in distinguishing between /ɛ/ and /æ/, and the acquisition of this contrast seems to lag behind. By examining cue weights over time, we were able to partially confirm the hypothesized developmental stages first proposed for Spanish learners of English (Escudero, 2000). However, we identified several unpredicted patterns: (1) some Korean learners used spectrum and duration in the opposite directions as native English listeners and (2) some learners relied only on spectrum at Time 1 and did not pass through a duration only stage. Furthermore, learners tended to rely on one cue or the other throughout acquisition. For the first time we used longitudinal data to examine individual’s cue weights over time for two vowel contrasts. There were two important findings: (1) individual differences in cue weighting are not merely random variability in the learner’s response patterns, but are systematically associated with the developmental trajectories of individual learners and (2) those trajectories vary according to the vowel contrast.

Chungnam National University, Daejeon, South Korea