Word-Final /s/-/z/ Omission in Vietnamese English

Southeast Asian learners of English, including those from Vietnam, frequently omit word-final consonants in their English speech. Previous work on Vietnamese learners of English is limited, and errors are typically usually attributed to first-language transfer effects. No large-scale empirical study on Vietnamese learners has been carried out to aid the development of an evidence-based pedagogy. This study uses authentic spoken data to compare lexical and morphological word-final /s/ and /z/ in the speech of sixteen Vietnamese adult learners of English. We discuss the relative impact of frequency of use, whether the instance of a target /s/ or /z/ is in a root or bound morpheme, and whether the preceding phoneme is a consonant or vowel. An overall omission rate of 28.4% of expected instances was found. Morphological {-s} when it is preceded by a consonant has the highest error rate (50.7%). A multilevel binary logistic regression was performed to ascertain the relative effects. Morphological words containing /s/ or /z/ were significantly more likely to be pronounced with the /s/ or /z/ absent than lexical words containing a /s/ or /z/, as were those in clusters compared to those with a preceding vowel. The results indicate that phonological effects and morphological effects are stacked and not multiplicative and that the observed omission rates are not solely attributable to L1 transfer effects. Frequency of use is also highly correlated with accuracy.