Vocabulary composition trajectories in late talkers, late bloomers, and typically developing toddlers

There is enormous early variability in vocabulary size for toddlers in their second year of life, making it hard to determine who is in the range of typical word learning, and who will continue to have persistent language delays that may require intervention. Though total vocabulary size is often used, in the present study we analyze the proportions of different word categories contributing to three talker groups' overall vocabularies during a year-long longitudinal study. Every month, 84 toddlers participated in a novel noun generalization task and their parents filled out the MacArthur-Bates Communicative Development Inventory (CDI), which yielded five categories: nouns, verbs, adjectives, grammar function words, and other words. Using their initial and final CDI scores, we divided our participants into persistent late talkers, late bloomers, and typically developing children. Results indicated that bloomers and persistent late talkers
differed in their initial proportion of adjectives as well as nouns, suggesting possible avenue for future investigation. Persistent late talkers showed delayed trajectories in every category (Figure 1). By further breaking down nouns into those solids and non-solids categorized by shape or material (or both), we investigated how each group’s noun composition related to their word-learning biases. Interesting relationships between vocabulary and these biases will be discussed. Results suggest analyzing the structure of young toddlers’ vocabularies may help differentiate
these groups for early identification, and may further indicate that these populations utilize
different strategies in accruing language. Future studies could investigate how to utilize
knowledge of vocabulary composition to aid intervention efforts.