Provide critical insight into the underlying mechanism by which walk onset impacts language development in the four groups of infants, ultimately enhancing the design of effective interventions to facilitate language development in children with ASD.  

Researchers have documented a spurt in language development following the transition from crawling to walking in typically-developing (TD) infants. Theorists have described this association as an epigenetic phenomenon, whereby the acquisition of one skill creates experiences that reorganize skills in other developmental domains. Under this theoretical framework, walk onset changes the context in which infants develop. It offers infants opportunities to move with more autonomy and willfulness, more freedom to explore objects and more opportunities to engage in social interactions. These new possibilities in turn have significant implications for language development. While the relation between walk onset and language development in TD infants is amply studied, limited studies have been conducted in children with autism spectrum disorder (ASD). Communication-related deficits, such as delay in first-word production and lack of communicative gestures (e.g., hand gestures, eye contacts), are among the most reported first concerns of parents of young children with ASD. Given the importance of language development in child development, it is critically important to understand the factors that impede and enhance language acquisition. Studying children at risk for communication-related deficits can provide rich insights into these factors, revealing insights that can inform the design of interventions to promote language development.  

Using the infant siblings of children with ASD [who are at elevated likelihood (EL) of developing ASD] and infants with no family history of ASD, a recent study found no significant language growth in EL infants with an eventual ASD diagnosis despite the occurrence of walk onset. The absence of a language spurt following walk onset may be an early marker of ASD and perhaps a particularly robust early marker because it focuses on two skills with known delays in children with ASD. One speculation is that ASD infants did not engage in the same quantity or type of social interactions as their TD counterparts. However, without a formal investigation, we cannot conclude if this explanation holds. Therefore, the proposed study aims to fill this important research gap by investigating the bidirectional influences of infant-caregiver interactions on language development in infants at elevated risk of ASD who will and will not receive an ASD diagnosis. In this study, we will recruit 120 EL infants who have a biological sibling with a confirmed diagnosis of ASD. The EL infants will be further classified into three outcome groups: infants who eventually receive an ASD diagnosis (EL-ASD), infants with language delay (EL-LD) and infants with no ASD diagnosis (EL-No ASD). Additionally, we will recruit 55 typicallydeveloping infants as a comparison group. A longitudinal observational study design will be employed to examine changes in infants’ locomotion status, infant-caregiver interactions, the intonational contour of caregiver’s utterances, and receptive and expressive language across the transition from crawling to walking. The findings from this proposed study can provide critical insight into the underlying mechanism by which walk onset impacts language development in the four groups of infants, ultimately enhancing the design of effective interventions to facilitate language development in children with ASD.