Discrimination of English Vowel Contrasts in Chinese Listeners in Relation to L2-to-L1 Assimilation

The Perceptual Assimilation Model (PAM)-L2 framework posits that the discriminability of L2 speech contrasts can be predicted from how L2 phones are assimilated to L1 categories. This study examined how such assimilation types relate to variability in L2 vowel discrimination within the PAM-L2 framework, with particular attention to assimilation overlap. Chinese listeners were tested with six English vowel contrasts (/i-ɪ/, /e-ɛ/, /æ-ɛ/, /ɑ-ɔ/, /ɔ-ʌ/, /u-ʊ/) using an assimilation task with goodness ratings and an AXB discrimination task. The vowel contrasts formed three Uncategorized-Categorized and two Uncategorized-Uncategorized contrasts, with both types exhibiting either partial or complete overlap, along with one Category-Goodness contrast. Discrimination results showed that partial versus complete overlap accounted for some differences in discrimination accuracy and absence of overlap between dominant L1 response categories likely facilitated discrimination even when secondary categories overlapped. Large differences in perceived goodness appeared to facilitate discrimination for a vowel contrast with complete overlap. The results are discussed in particular relation to the PAM-L2 account of the assimilation overlap-discrimination relationship, and additionally how the influence of overlap may be modulated by category-goodness differences in contributing to variability in L2 vowel discrimination.