PROJECT SUMMARY
Many infants in the United States and around the world grow up in bilingual environments, and their experience
is defined by caregivers' dynamic switching between two languages. Contrary to popular belief, only a tiny
minority of bilingual children grow up in a strict “one-person-one-language” environment. Instead, most
bilingual children regularly hear two languages from the same person, within the same conversation, and often
within the same sentence (e.g., “Look at the perro!”). Little is known about how young bilinguals learn through
the inherent alternations between languages. Our primary goal is to understand how bilingual infants and
toddlers learn two languages in the context of everyday switching across sentences, conversations, and
people. Based on findings from our previous NICHD-funded R03, we will test the overarching hypothesis
that language switching in bilingual environments is a key contributor to bilingual infants' language learning and
language outcomes. The proposed international, cross-lab project will test the same Spanish-English and
French-English bilingual children at 12, 24, and 36 months of age, using complementary behavioral,
household, and longitudinal measures of young bilinguals' learning from language switches. Aim 1 will use
eye-tracking and pupillometry experiments to investigate how bilingual infants and toddlers process and learn
from language switching across sentences (Exps. 1-2), conversations (Exps. 3-4), and people (Exps. 5-6). Aim
2 (Exp. 7) will use multi-day recordings of household language to investigate whether and how language
switching at home shapes early language processing and contributes uniquely to language and cognitive
outcomes. The proposed experiments will be conducted simultaneously with two distinct bilingual populations:
Spanish-English bilinguals in New Jersey, and French-English bilinguals in Montréal. Based on intersecting
sociolinguistic, demographic, and experiential differences between these communities, this approach will
address the crucial puzzle of generalizability in bilingualism research, i.e., whether findings are specific to one
population or whether they warrant generalized conclusions. In summary, the proposed studies will illuminate
an important, real-life challenge for language development: how bilingual infants and toddlers process familiar
words and learn new words from the complexities of dual-language input, both from moment to moment and in
aggregate. Findings will enable us to (a) generate a novel and comprehensive theoretical model of the
emergence of bilingualism in infants and toddlers, and (b) create and disseminate evidence-based guidelines
for fostering early bilingualism. Bilingual parents almost invariably assume that some bilingual environments
are better than others, and – like educators, pediatricians, and speech-language pathologists – they strive to
optimize children's dual-language learning and minimize the risk of language delays. Our complementary
measures of the dynamics of bilingual input and learning may lead to better ways of supporting infants' and
toddlers' pathways to bilingual proficiency.
