Lexical characteristics of expressive vocabulary in toddlers with autism spectrum disorder.

PURPOSE: Vocabulary is a domain of particular challenge for many children with autism spectrum disorder (ASD). Recent research has drawn attention to ways in which lexical characteristics relate to vocabulary acquisition. The current study tested the hypothesis that lexical characteristics account for variability in vocabulary size of young children with ASD, applying the extended statistical learning theory of vocabulary delay in late talkers (Stokes, Kern, & Dos Santos, 2012) to toddlers with ASD.

METHOD: Parents reported the words produced by toddlers with ASD (n = 57; age 21-37 months) or toddlers without ASD (n = 41; age 22-26 months) on the MacArthur-Bates Communicative Development Inventories. The average phonological neighborhood density, word frequency, and word length of each toddler's lexicon were calculated. These lexical characteristics served as predictors of vocabulary size.

RESULTS: Findings differed for toddlers with and without ASD and according to subsamples. Word length was the most consistent predictor of vocabulary size for toddlers with ASD.

CONCLUSIONS: Distinct relationships between lexical characteristics and vocabulary size were observed for toddlers with and without ASD. Experimental studies on distributional cues to vocabulary acquisition are needed to inform what is known about mechanisms of learning in neurodevelopmental disorders.