Patterns of Repetitive Behavior with Objects in Infants Developing ASD

Background:   Prior studies examining early manifestations of ASD have largely focused on social communication. However, it is increasingly recognized that repetitive behaviors also emerge early. Studies of infant siblings indicate that, at 12 months of age, infants who later developed ASD showed significantly more repetitive behaviors with objects (Ozonoff et al., 2008) and stereotyped motor mannerisms (Elison et al., 2014). However, it is unknown whether such behaviors are evident prior to the first birthday nor how they develop over the first years of life.

Objectives:   We evaluated infant behaviors with objects from 9 through 36 months to determine whether infants later diagnosed with ASD show distinct early patterns.

Methods:   Infant siblings of children with ASD (high-risk) or typical development (low-risk) were administered a task designed to elicit repetitive object use (Ozonoff et al., 2008) at 9, 12, 15, 18, 24, and 36 months of age. Of 151 infants, 59 were classified as low-risk typically developing (LR-TD), 76 as high-risk non-ASD (HR-Non-ASD), and 16 as high-risk ASD (ASD) at 36 months. Behavior was coded using seven codes, four of which were hypothesized to be developmentally typical (bang, drop/throw, shake, functional/symbolic play), and three hypothesized to be atypical (spin, rotate, unusual visual inspection). Employing a Generalized Estimating Equations approach using a negative binomial distribution with log link, we evaluated group differences in repetitive behavior frequencies between 9 and 36 months.

Results:   The interaction between type of repetitive behavior, visit, and outcome was significant (Wald χ²=308.29, df=60, p<.001). The groups showed few persistent differences in typical behaviors (Figure 1). The ASD and HR-Non-ASD groups displayed significantly less shaking at 9 months and more banging at 12 months relative to the LR-TD group, and the ASD group displayed significantly less dropping/throwing at 24 months relative to the LR-TD group. From 12-18 months, the LR-TD and HR-Non-ASD groups engaged in significantly more functional/symbolic play than the ASD group.

Regarding atypical behaviors (Figure 2), at 9 months, the ASD group engaged in significantly more unusual visual inspection than the LR-TD and HR-Non-ASD groups, persisting through 36 months. The ASD group also engaged in significantly less spinning than the LR-TD and HR-Non-ASD groups at 9 months. There were no differences in rotating, although trends for the ASD group being higher were evident at 15 and 18 months.

Conclusions: Unusual visual inspection of objects is present and stable as early as 9 months of age in infants developing ASD. This replicates and extends, in an independent sample, prior findings from 12-month-olds developing ASD (Ozonoff et al., 2008), demonstrating that unusual visual inspection is present earlier than previously thought and is one of the earliest behavioral predictors of ASD outcome yet documented. The groups showed few persistent differences in developmentally typical repetitive behaviors, suggesting that those developing ASD are not broadly repetitive overall, but display specific atypical repetitive behaviors with objects. These results suggest that close monitoring of unusual visual inspection may be an important aspect of early detection efforts and could be incorporated into screening and diagnostic tools.