A longitudinal study of individual differences in the acquisition of novel vowel contrasts


Most second language (L2) speech learning studies 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 with relative difficulty. 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 learners of English (12 adults & 14 children) participated in cue weighting experiments upon their arrival in Canada. They were tested on their perceptual weighting again approximately 4 and 8 months 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 children had significantly improved. Both Korean groups 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 categorizing /ɛ/-/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 initially relied only on spectrum and did not pass through a duration only stage. Furthermore, learners tended to rely on one cue or the other throughout acquisition.

Georgia State University, Atlanta, USA