Effects of consonantal context on perceptual assimilation of American English vowels by Japanese listeners

This study investigated the extent to which adult Japanese listeners' perce ived phonetic similarity of American English (AE) and Japanese (J) vowels v aried with consonantal context. Four AE speakers produced multiple instance s of the 11 AE vowels in six syllabic contexts /b-b, b-p, d-d, d-t, g-g, g- k/ embedded in a short carrier sentence. Twenty-four native speakers of Jap anese were asked to categorize each vowel utterance as most similar to one of 18 Japanese categories [five one-mora vowels, five two-mora vowels, plus /ei, ou/ and one-mora and two-mora vowels in palatalized consonant CV sylla bles, C(j)a(a), C(j)u(u), C(j)o(o)]. They then rated the "category goodness " of the AE vowel to the selected Japanese category on a seven-point scale. None of the 11 AE vowels was assimilated unanimously to a single J respons e category in all context/speaker conditions; consistency in selecting a si ngle response category ranged from 77% for /eI/ to only 32% for /ae/.. Medi an ratings of category goodness for modal response categories were somewhat restricted overall, ranging from 5 to 3. Results indicated that temporal a ssimilation patterns (judged similarity to one-mora versus two-mora Japanes e categories) differed as a function of the voicing of the final consonant, especially for the AE vowels, /i, u,I, epsilon, Lambda, upsilon/. Patterns of spectral assimilation O'udged similarity to the five J vowel qualities) of /I, epsilon, ae, Lambda/ also varied systematically with consonantal co ntext and speakers. On the basis of these results, it was predicted that re lative difficulty in the identification and discrimination of AE vowels by Japanese speakers would vary significantly as a function of the contexts in which they were produced and presented. (C) 2001 Acoustical Society of Ame rica.