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Evidence for an Infant Construct of Social Motivation and Predictive Validity for Autism Spectrum Disorder
Objectives: To investigate the evidence for a social motivation construct in infants, we leveraged existing data to 1) derive a parent-report index of social motivation in infants and 2) quantify the extent to which early social motivation accounts for variation related to ASD outcome at age 24 months.
Methods: Behavioral data were analyzed from over 400 participants in the Infant Brain Imaging Study, a prospective, multisite study of infants at high and low familial risk for ASD. High-risk infants have an older sibling with ASD; low-risk infants have no first-degree relatives with ASD. Participants were assessed at 6, 12, and 24 months of age, and items were selected from multiple parent-report measures, including the Vineland Adaptive Behavior Scales, First Year Inventory, Infant Behavioral Questionnaire-revised, and Macarthur-Bates CDI, based on face validity for indexing social motivation. Social motivation was operationalized as the disposition to preferentially orient to social stimuli; to seek, want, and like social interactions; and to exert effort to maintain social engagement (Chevallier, 2012). Item scores were uniformly weighted and summed to generate a “social motivation index” (SMI) score. A clinical-best-estimate procedure including the Autism Diagnostic Observation Schedule (ADOS) was used to diagnose ASD at age 24 months.
Results: The SMI demonstrated a continuous, unimodal score distribution, good internal consistency (Cronbach’s α=0.75-0.89) at all three ages (Fig. 1), and significant cross-age correlations (6-12 months: r=.58, p<.001, n=171; 12-24 months: r=.45, p<.001, n=183; 6-24 months r=.27, p<.001, n=210), suggesting trait-like stability (Fig. 2). Lower SMI scores were observed by age 6 months for infants later diagnosed with ASD (6 months: t(298)=-3.15, p=.002) and 6-month SMI scores significantly correlated with ADOS calibrated severity scores at 24 months (r=-.21, p<.001). A binary logistic regression model testing the effect of sex and 6-month SMI on categorical ASD diagnosis at 24 months was significant (χ2(2)=18.52, p<.001), with sex and SMI each accounting for 5% of the variance. The effect of SMI remained significant when the 6-month Mullen Early Learning Composite, a measure of general cognitive development, was added to the model. The 6-month Vineland Socialization subscale, a parent-report metric of social function, did not significantly predict ASD diagnosis when substituted for SMI in the model.
Conclusions: These findings provide initial evidence for a measurable social motivation construct in infancy which shows predictive validity for ASD by 6 months of age. ASD-related SMI score differences suggest that further characterization of social motivation in infancy could promote earlier identification of children with ASD who would benefit from intervention.