Current theories of cross-language speech perception claim that patterns of perceptual assimilation of non-native segments to native categories predict relative difficulties in learning to perceive (and produce) non-native phones. Cross-language spectral similarity of North German (NG) and American English (AE) vowels produced in isolated hVC(a) (di)syllables (study 1) and in hVC syllables embedded in a short sentence (study 2) was determined by discriminant analyses, to examine the extent to which acoustic similarity was predictive of perceptual similarity patterns. The perceptual assimilation of NG vowels to native AE vowel categories by AE listeners with no German language experience was then assessed directly. Both studies showed that acoustic similarity of AE and NG vowels did not always predict perceptual similarity, especially for "new" NG front rounded vowels and for "similar" NG front and back mid and mid-low vowels. Both acoustic and perceptual similarity of NG and AE vowels varied as a function of the prosodic context, although vowel duration differences did not affect perceptual assimilation patterns. When duration and spectral similarity were in conflict, AE listeners assimilated vowels on the basis of spectral similarity in both prosodic contexts.

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Strange et al. [J. Acoust. Soc. Am. 115, 1791-1807 (2004)] reported that North German (NG) front-rounded vowels in hVp syllables were acoustically intermediate between front and back American English (AE) vowels. However, AE listeners perceptually assimilated them as poor exemplars of back AE vowels. In this study, speaker- and context-independent cross-language discriminant analyses of NG and AE vowels produced in CVC syllables (C=labial, alveolar, velar stops) in sentences showed that NG front-rounded vowels fell within AE back-vowel distributions, due to the "fronting" of AE back vowels in alveolar/velar contexts. NG [I, e, epsilon, inverted c] were located relatively "higher" in acoustic vowel space than their AE counterparts and varied in cross-language similarity across consonantal contexts. In a perceptual assimilation task, naive listeners classified NG vowels in terms of native AE categories and rated their goodness on a 7-point scale (very foreign to very English sounding). Both front- and back-rounded NG vowels were perceptually assimilated overwhelmingly to back AE categories and judged equally good exemplars. Perceptual assimilation patterns did not vary with context, and were not always predictable from acoustic similarity. These findings suggest that listeners adopt a context-independent strategy when judging the cross-language similarity of vowels produced and presented in continuous speech contexts.

This study investigated the extent to which adult Japanese listeners' perceived phonetic similarity of American English (AE) and Japanese (J) vowels varied with consonantal context. Four AE speakers produced multiple instances 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 Japanese 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 syllables, 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 response category in all context/speaker conditions; consistency in selecting a single response category ranged from 77% for /eI/ to only 32% for /ae/. Median ratings of category goodness for modal response categories were somewhat restricted overall, ranging from 5 to 3. Results indicated that temporal assimilation patterns (judged similarity to one-mora versus two-mora Japanese categories) differed as a function of the voicing of the final consonant, especially for the AE vowels, /see text/. Patterns of spectral assimilation (judged similarity to the five J vowel qualities) of /see text/ also varied systematically with consonantal context and speakers. On the basis of these results, it was predicted that relative 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.

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