The roles of L1 transfer, L2 exposure, and morphological salience in bilingual children's L2 English morphological development.

Introduction: The present study aims to advance our understanding of bilingual children's L2 morpheme acquisition variability by examining the child-internal factor of L1 transfer, child-external factor of L2 exposure, as well as the linguistic factor of morphological salience. Method: Drawing on naturalistic conversational data from a corpus of bilingual children's language samples, we analyzed the production accuracy of five English inflectional morphemes in 21 language samples from Spanish-English bilingual children and 25 language samples from Mandarin-English bilingual children. The two groups were age-matched and gender-balanced, with a mean age of 5 years and 1 month (range: 3; 8-7; 5). Binomial logistic mixed-effects models were employed to examine the accuracy of L2 morpheme production as influenced by L1 transfer, L2 input quantity (months of English exposure), input quality (morphological richness & lexical diversity), and the morphological salience of the target morphemes. Results: The results revealed a significant effect of L1 transfer, with Spanish-English bilinguals demonstrating higher accuracy than Mandarin-English bilinguals, particularly for English plural -s and articles. Besides, months of English exposure emerged as a significant positive predictor of L2 morpheme production accuracy. As regards input quality, while lexical diversity positively contributed to morpheme accuracy in both groups, morphological richness negatively affected morpheme production accuracy among Mandarin-English bilinguals. In addition, our descriptive analyses of morphological salience factors indicate that, across both groups of children, perceptual salience, morphophonological regularity, syntactic category and semantic complexity influence morpheme production accuracy to different degrees. Discussion: The study suggests that L1 transfer plays a critical role in L2 English morpheme production accuracy and underscores the importance of L2 input quantity and quality, such as lexical diversity, in explaining variability in bilingual children's morpheme acquisition. Additionally, difficulties in producing English morphemes may be associated with factors related to morphological salience. Overall, the findings underlie the importance of L1 transfer, L2 exposure, morphological salience in bilingual children's L2 morpheme acquisition.