Code-switching is a common phenomenon in bilingual communities, but little is known about bilingual parents’ code-switching when speaking to their infants. In a pre-registered study, we identified instances of code-switching in day-long at-home audio recordings of 21 French–English bilingual families in Montreal, Canada, who provided recordings when their infant was 10 and 18 months old. Overall, rates of infant-directed code-switching were low, averaging 7 times per hour (6 times per 1,000 words) at 10 months and increasing to 28 times per hour (18 times per 1,000 words) at 18 months. Parents code-switched more between sentences than within a sentence; this pattern was even more pronounced when infants were 18 months than when they were 10 months. The most common apparent reasons for code-switching were to bolster their infant's understanding and to teach vocabulary words. Combined, these results suggest that bilingual parents code-switch in ways that support successful bilingual language acquisition.

Aims and Objectives: Bilingualism is a complex construct, and it can be difficult to define and model. This paper proposes that the field of bilingualism can draw from other fields of psychology, by integrating advanced psychometric models that incorporate both categorical and continuous properties. These models can unify the widespread use of bilingual and monolingual groups that exist in the literature with recent proposals that bilingualism should be viewed as a continuous variable. Approach: In the paper, we highlight two models of potential interest: the factor mixture model and the grade-of-membership model. These models simultaneously allow for the formation of different categories of speakers and for continuous variation to exist within these categories. We discuss how these models could be implemented in bilingualism research, including how to develop these models. When using either of the two models, researchers can conduct their analyses on either the categorical or continuous information, or a combination of the two, depending on which is most appropriate to address their research question. Conclusions: The field of bilingualism research could benefit from incorporating more complex models into definitions of bilingualism. To help various subfields of bilingualism research converge on appropriate models, we encourage researchers to pre-register their model selection and planned analyses, as well as to share their data and analysis scripts. Originality: The paper uniquely proposes the incorporation of advanced statistical psychometric methods for defining and modeling bilingualism. Significance: Conceptualizing bilingualism within the context of these more flexible models will allow a wide variety of research questions to be addressed. Ultimately, this will help to advance theory and lead to a fuller and deeper understanding of bilingualism.

Models of monolingual literacy propose that reading acquisition builds upon children’s semantic, phonological, and orthographic knowledge. The relationships between these components vary cross-linguistically, yet it is generally unknown how these differences impact bilingual children’s literacy. A comparison between Spanish-English bilingual and English monolingual children (ages 6–13, N=70) from the U.S. revealed that bilinguals had stronger associations between phonological and orthographic representations than monolinguals during English reading. While vocabulary was the strongest predictor of English word reading for both groups, phonology and morpho-syntax were the best predictors of Spanish reading for bilinguals. This comparison reveals distinct developmental processes across learners and languages, and suggests that early and systematic biliteracy exposure at home and through afterschool programs can influence children’s sound-to-print associations even in the context of language-specific (monolingual) reading instruction. These findings have important implications for bilingual education as well as theories that aim to explain how learning to read across languages has a positive impact on the acquisition of literacy.

Bilingual children hear sentences that contain words from both languages, also known as code-switching. Investigating how bilinguals process code-switching is a crucial component in understanding bilingual language acquisition, because young bilinguals experience processing costs and reduced comprehension when encountering code-switched nouns. Studies have yet to investigate if processing costs are present when children encounter code-switches at other parts of speech within a sentence. The current study examined how 30 young bilinguals (age range: 37 – 48 months) process sentences with code-switches at an uninformative adjective before the target noun (e.g., “Can you find le bon [the good] duck?) compared to single-language sentences (e.g., “Can you find the good duck?”). Surprisingly, bilingual children accurately identified the target object in both sentence types, contrasting with previous findings that sentences containing code-switching lead to processing difficulties. The functional information a code-switch carries may contribute to bilingual children’s sentence processing.