Clarifying the developmental association between gesture and later vocabulary for autistic children.

Gestures serve as both a communication and a word-learning tool, with typically developing children consistently showing that early gestures are positively associated with later vocabulary skills. However, many autistic children experience delays and challenges in both gesture and vocabulary skills, and studies also show mixed gesture-vocabulary associations; thus, it is unclear whether gestures in autistic children support emerging vocabulary skills. To address previous conflicting findings, the current conceptual replication study uses linear models with a large sample (N = 451) of 12- to 24-month-old English-raised infants to investigate whether gestures are associated with expressive and receptive vocabulary. Using the infant-sibling design, gesture-vocabulary associations and group moderation were investigated in three groups: infant-siblings of autistic children who later meet the criteria for autism themselves (HL-ASD, n = 73), infant-siblings who did not meet criteria for autism (HL-Neg, n = 238), and a control group without a family history of autism (LL-Neg, n = 140). Both LL-Neg and HL-ASD groups showed positive associations between 12-month gestures and 18-month receptive vocabulary; however, only the LL-Neg group showed a positive association between 12-month gestures and 18-month expressive vocabulary. For 12-month gestures and 24-month receptive and expressive vocabulary, the LL-Neg and HL-Neg groups showed positive association, whereas the HL-ASD group did not. Similarly, the LL-Neg and HL-Neg groups showed positive associations between 18-month gestures and 24-month vocabulary, but the HL-ASD did not. Overall, the LL-Neg group showed significant gesture-vocabulary associations across all tested models, while the HL-ASD only showed one significant positive association.