Testing theories of the vocabulary spurt with monolingual and bilingual infants.

Sometime before their second birthday, many children have a period of rapid expressive vocabulary growth called the vocabulary spurt. Theories of the underlying mechanisms differ: Accumulator models emphasize the accumulation of experience with words over time to yield a spurtlike pattern, while cognitive models attribute the spurt to cognitive changes. To test these theories, English-French monolingual and bilingual children with different exposure to each language were studied. Dense, longitudinal data were analyzed from 45 infants aged 16-30 months, whose expressive vocabulary was measured on a total of 617 occasions in English and/or French. Single-language (English and/or French), concept (number of concepts lexicalized across both languages), and word (sum of both languages) vocabulary scores were computed. Infants' exposure to each language and their exposure balance were measured using a language exposure questionnaire. Logistic curves were fitted to each infant's data to estimate the timing (midpoint) and steepness (slope) of the vocabulary spurt in single-language, concept, and word vocabularies. Seventy-six percent of infants showed a spurt in at least one vocabulary type, and bilinguals were less likely to show one in their nondominant than their dominant language. For single-language vocabulary, infants with more exposure to a language had earlier spurts. For combined vocabularies (concept and word), monolinguals and unbalanced bilinguals had earlier and steeper spurts than balanced bilinguals. Results better support the predictions of accumulator models than cognitive theories and show that infants follow different vocabulary acquisition trajectories based on their language background. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Patterns of language switching and bilingual children's word learning: An experiment across two communities.

Language switching is common in bilingual environments, including those of many bilingual children. Some bilingual children hear rapid switching that involves immediate translation of words (an 'immediate-translation' pattern), while others hear their languages most often in long blocks of a single language (a 'one-language-at-a-time' pattern). Our two-site experimental study compared two groups of developing bilinguals from different communities, and investigated whether differences in the timing of language switching impose different demands on bilingual children's learning of novel nouns in their two languages: do children learn differently if they hear a translation immediately vs. if they hear translations more separated in time? Using an at-home online tablet word learning task, data were collected asynchronously from 3- to 5-year-old bilinguals from French-English bilingual families in Montreal, Canada (N = 31) and Spanish-English bilingual families in New Jersey, USA (N = 22). Results showed that bilingual children in both communities readily learned new words, and their performance was similar across the immediate-translation and one-language-at-a-time conditions. Our findings highlight that different types of bilingual interactions can provide equal learning opportunities for bilingual children's vocabulary development.