Responding to Joint Attention Mediates the Relation between Early Imitation and Later Expressive Language in Infants at High and Low Risk for Autism Spectrum Disorder

Abstract

Infant siblings of children with autism (HR infants) are at greater risk for language delay than infants with typically developing older siblings (LR infants). This study examined the early developmental pathways that underlie language growth in HR and LR infants using a prospective longitudinal design. Two early social-communicative skills that predict expressive language in both children with autism and those with typical development are motor imitation (i.e., imitating the actions of others) and responding to joint attention (i.e., following the direction of another person's interest; RJA). We hypothesized that: (1) RJA would mediate the association between imitation and expressive language over the first two years of life, and (2) mediation would be stronger for HR infants than LR infants. Imitation, RJA, and expressive vocabulary were assessed in 84 infants (50 HR) between 12 and 18 months. Results revealed that 15-month RJA mediated the association between 12-month imitation and 18-month expressive vocabulary, even after controlling for earlier levels of RJA and language. A conditional direct effect was also found; after accounting for the mediation effect, 12-month imitation directly affected 18-month expressive vocabulary for LR, but not HR, infants. These results support a developmental sequence for language development that can inform future intervention efforts for children at risk for developmental challenges.