How do infants become word meaning experts? This registered report investigated the structure of infants' early lexical representations by manipulating the typicality of exemplars from familiar animal categories. 14- to 18-month-old infants (N = 84; 51 female; M = 15.7 months; race/ethnicity: 64% White, 8% Asian, 2% Hispanic, 1% Black, and 23% multiple categories; participating 2022–2023) were tested on their ability to recognize typical and atypical category exemplars after hearing familiar basic-level category labels. Infants robustly recognized both typical (d = 0.79, 95% CI [0.54, 1.03]) and atypical (d = 0.70, 95% CI [0.46, 0.94]) exemplars, with no significant difference between typicality conditions (d = 0.14, 95% CI [−0.08, 0.35]). These results support a broad-to-narrow account of infants' early word meanings. Implications for the role of experience in the development of lexical knowledge are discussed.

Questions about early word knowledge pervade the literature on both typical and atypical language trajectories. To determine which words an infant knows, researchers have relied on two types of measures—caregiver‐report and eye‐gaze behavior. When these measures are compared, however, their results frequently fail to converge, making it difficult to ascertain whether a given infant knows a given set of words. What are the reasons for these misalignments in gold‐standard tasks that are designed to investigate the same underlying construct, and can convergent validity be improved? The current study was designed to investigate multiple methodological features of caregiver‐report and looking‐while‐listening (LWL) tasks hypothesized to contribute to their alignment. American English‐learning infants (18–20 months; N = 52) completed an LWL task assessing their understanding of eight early‐acquired words. Caregivers reported their child's knowledge of the same eight words, as well as their confidence in their responses and the amount of time they spend with their child. Overall, caregivers’ reports of word knowledge did not predict infants’ eye‐gaze behavior. However, the measures were more likely to be aligned when caregivers reported higher confidence in their responses. Caregivers’ reports about both the target and the distractor word on each trial were related to infants’ eye‐gaze behavior, suggesting that LWL tasks capture knowledge about the labels of both objects tested, not just the label of the target object. The results suggest several critical methodological modifications that could be implemented to improve the measurement validity of both caregiver‐report and eye‐gaze measures of word comprehension. Summary: This study provides novel insights to improve the validity of infant vocabulary measurement by highlighting factors that explain differences between caregivers' reports and eye‐gaze behavior. Caregivers’ reports of individual word knowledge failed to converge with infants’ eye‐gaze behavior during a looking‐while‐listening (LWL) task. Caregivers’ reports of individual word knowledge aligned more strongly with their infant's eye‐gaze behavior when caregivers reported more confidence in their responses. Caregivers’ reports of both the target and the distractor words predicted infants’ eye gaze behavior.

The role of function in toddlers' object labeling has been debated for decades in developmental science. We aimed to clarify the relation between toddlers' understanding of functions and words using a set of everyday objects that varied in the number of associated functions (e.g., balls can be bounced, thrown, or rolled while toothbrushes primarily brush teeth). Forty 23- to 25-month-old monolingual English-learning toddlers completed a preferential looking paradigm in which objects were used in conventional and unconventional ways, designed to measure expectations about object functional expectations. We also measured toddlers' lexical knowledge about these objects using a looking-while-listening task. Finally, we assessed productive vocabulary size using the MacArthur-Bates Communicative Development Inventory: Words and Sentences. The results suggest that toddlers have expectations about the functions of some objects, but not others. In particular, these expectations were stronger for objects that are tightly linked with their functions in everyday experiences, and for children who have larger vocabularies. These findings also suggest that toddlers' ability to demonstrate functional knowledge may depend on the specific objects included in the task.

This study examined how bilingualism and speaker variability influence children’s receptive and expressive cross-situational word learning (CSWL) performance. Effects of bilingualism were assessed both categorically (monolingual vs. bilingual) and continuously (length of bilingual experience). Ninety-five children aged 5–9 years completed a CSWL task under single-speaker and multiple-speaker conditions. Receptive performance was comparable between monolingual and bilingual children and was not influenced by speaker variability. However, within the bilingual sample, greater length of bilingual experience predicted stronger receptive learning. Expressive performance revealed a different pattern: monolinguals produced novel words more accurately than bilinguals. Within bilingual children, longer bilingual experience was associated with higher expressive accuracy. Speaker variability did not significantly affect expressive outcomes, nor did its effects interact with the language group or the length of bilingual experience. These findings suggest that children form representations during CSWL that support partial productions of newly learned words, while also indicating that expressive outcomes may be more sensitive to bilingual experience than receptive outcomes. Together, the results underscore the importance of considering both outcome modality and fine-grained measures of language experience when evaluating bilingual influences on novel word learning.