Differences in Early Vocabulary Development from 18–36-month-old Late Talkers and Typically Developing Toddlers of Matched Age and Expressive Vocabulary Levels

Objectives: This study aimed to examine information about two-word combinations of 18–36-month-old toddlers and identify predictors of the two-word combinations in 18–36-month-old late talkers, and age-matched, and expressive vocabulary-matched typically developing toddlers. Methods: A total of 1,051 toddlers participated in this study, including 25–36-month-old late-talkers (LT) (N = 43), typically developing age-matched (AM) toddlers (N = 847), and typically developing expressive vocabulary-matched (VM) toddlers aged 18–24 months (N= 161). The study examines the data collected from Korean MacArthur-Bates Communicative Development Inventories (K M-B CDI; Pae & Kwak, 2011). The dataset was obtained through the Wordbank website (wordbank.stanford.edu). Results: There were significant differences in the two-word combination utterance for each group. The most frequently represented group of the two-word combinations was the AM group with 12.6%, followed by the LT group with 4.7%, and the VM group with 0.6%. The factor significantly correlated with the two-word combinations was consistently found to be receptive vocabulary in all groups. In addition, the receptive vocabulary factor showed significant explanatory power for the two-word combinations only in the AM group. Conclusion: The LT group showed more two-word combinations yields than the younger VM group, suggesting that the age effect cannot be ignored for two-word combinations. Regarding the production of word classes, the percentage of noun production was the highest out of all the word classes, however the LT group’s production was significantly lower than the AM groups. In addition, the LT group lacked the proportion of adjectives compared with the VM group, which suggests that adjectives may be particularly difficult as they are used for describing abstract properties.