Learning language in autism: maternal linguistic input contributes to later vocabulary.

It is well established that children with typical development (TYP) exposed to more maternal linguistic input develop larger vocabularies. We know relatively little about the linguistic environment available to children with autism spectrum disorders (ASD), and whether input contributes to their later vocabulary. Children with ASD or TYP and their mothers from English and French-speaking families engaged in a 10 min free-play interaction. To compare input, children were matched on language ability, sex, and maternal education (ASD n = 20, TYP n = 20). Input was transcribed, and the number of word tokens and types, lexical diversity (D), mean length of utterances (MLU), and number of utterances were calculated. We then examined the relationship between input and children's spoken vocabulary 6 months later in a larger sample (ASD: n = 19, 50-85 months; TYP: n = 44, 25-58 months). No significant group differences were found on the five input features. A hierarchical multiple regression model demonstrated input MLU significantly and positively contributed to spoken vocabulary 6 months later in both groups, over and above initial language levels. No significant difference was found between groups in the slope between input MLU and later vocabulary. Our findings reveal children with ASD and TYP of similar language levels are exposed to similar maternal linguistic environments regarding number of word tokens and types, D, MLU, and number of utterances. Importantly, linguistic input accounted for later vocabulary growth in children with ASD.