Project Summary. Over the last several decades, developmental language scientists have sought to understand the effects of dual language input on children’s vocabulary outcomes. Much of this work has been correlational and has focused on static standardized measures of vocabulary size in typically developing bilingual children, excluding late talkers – children with atypically small vocabularies. Yet, about 25% of bilingual 2-year-olds are late talkers compared to only 10-15% of white monolingual cohorts. Although an important predictor of later outcomes, vocabulary size reveals little about children’s semantic structure – how word meanings are represented, organized, and connected. Computational and empirical studies in monolinguals suggest that children’s semantic structure 1.) reflects the statistical regularities and semantic relationships in their language environments; and 2.) predicts word learning over and above vocabulary size. Critically, it remains unclear how children’s lexicons reflect dual language input, and whether different semantic structures yield distinct adaptations to word learning in dual language contexts. Therefore, the primary objective of this proposal is to examine interactions between dual language input, semantic structure, and word learning in bilingual TD and LT toddlers. We will test 80 Spanish-English matched typical- and late-talking bilingual toddlers aged 24 – 30 months. In Aim 1, we will use semantic network approaches to model children’s lexicons in both languages and characterize the relationship between dual language input and children’s semantic structure. In Aim 2, we will examine the relationship between semantic structure and statistical word learning in single and dual language contexts. We will also analyze whether children’s semantic network properties in both languages modeled in Aim 1 predict word learning performance across semantic and dual language experimental conditions. In Aim 3, we will analyze late- talker status as a predictor and compare 40 typical talkers to 40 late talkers to examine whether the relationships among dual language input, semantic structure, and word learning differ between groups. This career development proposal includes an expert team of mentors from Psychology, Computer Science, Communication Sciences and Disorders, Education and Public Health. The candidate will receive training in observational methodology and parent-child interactions; experimental and eye-tracking methodology for toddlers; and network science approaches. The long-term goals of this work and specialized training are to examine language trajectories longitudinally in bilingual learners; and to develop novel clinician- and parent-mediated interventions for bilingual children via behavior and network science approaches. The career goals align closely with the strategic objectives of NIDCD, including to capitalize on advances in basic research to enhance our understanding of normal function and disorde...