The Relationship between English Speech Rhythm and Vowel Reduction in Production : Comparison between Japanese EFL Learners and Native English Speakers

Abstract

It has often been said that Japanese EFL learners have-difficulty in producing English speech rhythm, which has a close relationship to vowel reduction such as schwa. This seems to be a phenomenon caused by Japanese speech rhythm with little vowel reduction and little variability in vowel durations between successive morae. This study fries to investigate how English speech rhythm and vowel reduction are related in terms of the vowel duration and the formant space. Vowel durations of speech samples are measured, and pairwise variability index (PVI) values are calculated and compared quantitatively between Japanese EFL learners and native speakers of English. The first formant (F1) and the second formant (F2) of the unstressed vowels are also computed and the dispersion of F1/F2 is compared between the two groups in order to examine the qualitative difference of schwa. The data obtained in the study give marked contrast between them in both PVI and F1/F2 formant distribution. Vowel reduction produced by Japanese EFL learners shows a signficantly lower PVI and a greater distance from the centroid in the F1/F2 ,formant space than does that of native English speakers. The results suggest that then is a good possibility that English speech rhythm produced by Japanese EFL learners is influenced by their native tongue mora-timed rhythm.