Intelligibility and acoustic correlates of Japanese accented English vowels

To produce near-native American English (AE) vowels, Japanese speakers must extend their five vowel system with at least six new vowels. Three experiments have been conducted to acquire both perceptual and acoustic measures about Japanese accented English (JE) vowels. Six non-back vowels of AE in several phonetic environments were recorded from four Japanese male talkers with moderate English skills. Intelligibility was assessed by a panel of six Americans as the percent of JE vowels identified as intended. The first experiment was an open-set identification task. Two vowels, /i/ and /e/ were fully intelligible (>98%) while others ranked from 81% (/ε/) to 23% (/∧/) intelligible. The second experiment used minimal-pair responses to assess intelligibility in terms of three acoustic properties of vowels, the spectral target, dynamic formants and duration. The results indicated that the spectral property was not communicated effectively, dynamics were partially effective, and duration was used effectively. In the third experiment a stepwise multiple linear regression analysis determined how these acoustic properties contributed to the intelligibility. For the two vowels analyzed, /x/ and /æ/, the direction and extent of the formant movement of JE vowels in relation to the AE targets was the vowel property that contributed the most to intelligibility