Context and speaker effects in the perceptual assimilation of German vowels by American listeners

To directly assess the influence of consonantal context and speaker differences on cross-language perceptual similarity of vowels, speakers of American English (AE) were asked to categorize and rate the goodness of fit of North German (NG) vowels to native categories. Four speakers produced the 14 NG monophthongs in 5 CVC contexts in a carrier sentence. Twelve listeners were presented with each speaker's utterances with vowels and consonantal contexts randomly sequenced. Overall perceptual assimilation patterns showed large variations in the perceived similarity of NG vowels even for those vowels which are considered phonetically similar across languages. The front rounded NG vowels, which do not occur as distinctive phonemes in AE, were almost always assimilated to back rounded AE vowels. Significant context and speaker effects were shown for most of the NG vowels. This suggests that context-free descriptions of cross-language phonetic similarity of vowels will not be adequate in predicting relative perceptual difficulty in learning to differentiate non-native vowels. These results also have implications for theories about the nature of the representation of native-language phonetic categories.