Non-native vowel production accuracy and variability in relation to overall intelligibility

Abstract

Previous research suggests that accuracy (i.e., distance to the average location of native productions) has less effect on adaption to non-native speech than category variability [e.g., Wade et al., Phonetica 64, 122-144 (2007)]. Here we investigate the relationship between overall intelligibility of Mandarin-accented English for native English listeners and (a) vowel production accuracy, and (b) vowel production consistency. Intelligibility estimates were based on sentence-in-noise recognition accuracy scores. Vowel accuracy and consistency estimates were based on formant measurements of point vowels (/i/, /u/, /ae/, and /a/) extracted from words in the sentence materials that were presented to listeners for intelligibility testing (8-20 samples/vowel/talker). If listeners have expectations about a vowel category location based on accumulated exemplar storage, then greater accuracy (smaller Euclidean distance to native category mean) should be positively related to intelligibility. If listeners are sensitive to vowel category distributions, then greater consistency (smaller standard deviation of f1 or f2 within categories) should be beneficial to intelligibility. A mixed effects linear model revealed that only consistency was a significant predictor of intelligibility. Accuracy was not a significant predictor. This result suggests that intra-speaker variability is detrimental to L2 intelligibility, regardless of distance to native categories.