Perceptual assimilation of American English vowels by Japanese listeners

Abstract

The present study examined Japanese (J) speakers' perceptual assimilation of 11 American English (AE) vowels produced by four male speakers in two sets of materials: /hVba/ disyllables spoken in citation-form (lists) and in /hVb/ syllables embedded in a short carrier sentence. J listeners were asked to select the J vowel category to which each AE vowel was most similar and to rate its category goodness on a 7-point scale. While the overall pattern of assimilation to the five Japanese (J) vowel qualities (spectral assimilation pattern) was partially predictable on the basis of cross-language phonetic similarities, there were some unexpected results, and spectral assimilation patterns differed across disyllable and sentence conditions for 4 of the 11 vowels. There were also large differences across the two sets of materials in assimilation of long and short AE vowels to J long (2-mora) and short (1-mora) vowel categories (temporal assimilation pattern). The long AE vowels were perceived as similar to long J vowels only when they were produced and presented in sentence context. In a second study in which the final /a/ portions of the disyllables were electronically shortened, assimilation of long AE vowels to long J categories did not differ from the original disyllable condition. This suggests that the better temporal differentiation of long and short AE vowels in the sentence condition was due to the presence of a larger rhythmic context. Acoustical analysis of the stimuli indicated that some, but not all, of the differences in spectral and temporal perceptual assimilation patterns across speakers and conditions could be accounted for by differences in acoustic structure (production differences). Implications for theories of L2 speech learning and for training studies of L2 vowels are discussed.