How similar are the formants in the speech of bilingual speakers?

This study investigated whether a stronger accent in the L2 of Cantonese-English bilingual speakers with high levels of English proficiency correlates with greater convergence of corresponding vowels (four monophthongs (/i a (a) c u/ and five diphthongs /ai au ei ci ou (eu)/) between their two languages in identical phonetic environments. No consistent effect of accent rating was found in either acoustic or perceptual similarity measures. Much individual variation and vowel-specific patterns were observed. The results demonstrate that the formant patterns in one language or one vowel cannot predict those in another language or another vowel, even with highly comparable materials and speakers with a relatively strong accent. Possible reasons and implications for the lack of correlation between accentedness and vowel convergence are discussed.