The Phonological Similarity Pattern of Words Contributing to Expressive Vocabulary in 18- to 36-Month-Old Toddlers

Objectives: In this study, the Korean MacArthur-Bates Communicative Development inventory (K M-B CDI), a standardized parent-report questionnaire, was used for analyzing the vocabulary development phonological similarity pattern of 18- to 36-month-old toddlers. Methods: We investigated the extent to which phonological similarity explains the expressive vocabulary according to the time differences in Experiment 1 and the group characteristics in Experiment 2. In Experiment 1, a total of 18 toddlers aged 18-36 months participated in this study. In Experiment 2, a total of 151 toddlers (typically developing children [TD]= 134, late talkers [LT]= 17) participated. Phonological similarity scores were calculated depending on the similarity rate between two words. Phonological similarity was divided into three conditions and defined as P1 (66%), P2 (75%), and P3 (80%). We obtained overall expressive vocabulary and phonological similarity through the K M-B CDI. Results: In Experiment 1, P1, which shares relatively fewer phonemes between words, seems to be the best predictor of overall expressive vocabulary consistently. In Experiment 2, all the phonological similarity conditions explained the overall expressive vocabulary scores in the TD group, but P1 was a significant explaining factor for expressive vocabulary in LT group. Conclusion: Although expressive vocabulary increased sharply, P1, which shares relatively fewer phonemes between words, consistently appeared to be the best predictor of overall expressive vocabulary. At least until the age of three, words with low phonological similarity are more easily distinguished, and this ability also seems to contribute to expressive vocabulary.