Contextual variation in the acoustic and perceptual similarity of North German and American English vowels

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, ε, inverted c sign] 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.