Untangling Bilingualism: Using Code-Switching to Understand Bilingual Language Development

Switching between two languages, or code-switching, is common in bilingual communities. However, little is known about the code-switching young bilinguals hear in their daily lives and how they process it. This dissertation investigated these two aspects of code-switching and proposed new models for defining bilingualism. Bilingualism is difficult to define and model. In Chapter 2, I proposed that bilingualism researchers can integrate psychometric models, such as the factor mixture model and the grade-of-membership model, which incorporate both categorical and continuous properties. Such models can unify traditional approaches of defining bilingual groups with newer views of bilingualism as a continuous variable. These models will allow researchers to address a variety of research questions, advance theory, and lead to a deeper understanding of bilingualism. In Chapter 3, I analyzed French–English parents’ code-switching in day-long at-home audio recordings, provided when their infant was 10 and 18 months old. Code-switching was relatively infrequent: an average of 7 times per hour (6 times/1,000 words) at 10 months, increasing to 28 times per hour (18 times/1,000 words) at 18 months. Parents code-switched more between sentences than within a sentence, and this pattern became more pronounced when infants were 18 months. Parents appeared to code-switch most frequently to bolster their infant’s understanding and teach vocabulary, suggesting that code-switching may support successful bilingual language development. In Chapter 4, I investigated how bilingual children process code-switching, examining how 3-year-old bilinguals process sentences with code-switches at an uninformative determiner-adjective pair before the target noun (e.g., “Can you see el buen [sp. the good] duck?) compared to single-language sentences (e.g., “Can you see the good duck?”). Children were unexpectedly accurate at identifying the target noun in both sentence types, contrasting with previous findings that code-switching leads to processing difficulties. Surprisingly, exploratory results suggested that code-switching may have boosted comprehension for certain children. In sum, this dissertation has illustrated how code-switching may support bilinguals’ language development. I discovered that parents code-switch to support their child’s learning and showed that children do not always have difficulty processing code-switching. Bilingualism is a multi-faceted phenomenon, and nuanced research is needed to capture this variability