Infant Emotional Responsiveness and Autism Risk

Background:  Emotional responsiveness is important for maintaining positive interactions between social partners. Individuals with autism spectrum disorder (ASD) show impairments in emotional responsiveness. A crucial component of emotional responsiveness is responsive social smiling, in which one social partner’s smile appears to be contingent on the other’s smile. In typically developing children, responsive social smiling develops within the first six months of life; however, less is known about early smiling behaviors, particularly responsive social smiling, in infants at elevated risk for ASD. 

Objectives:  We utilized a micro-coding approach to investigate the relation between smiling during early parent-infant interactions and later ASD diagnosis in children at varying risk for ASD.

Methods:  Participants were 64 children at high- or low-risk for ASD from diverse ethnic/racial backgrounds. High-risk children had at least one older sibling with ASD, while low-risk children had no known family history of ASD. Smiling behaviors were measured at 6 months of age during the Face-to-Face/Still Face paradigm. We focused on the Face-to-Face (parent interacts with infant normally for 3 minutes) and Reunion (parent re-initiates interaction with infant for 3 minutes after period of non-responsiveness) episodes. Parent and infant smiling was reliably coded for presence or absence on a frame-by-frame basis. Two smiling variables were calculated across episodes: Frequency of Smile Onsets and Contingent Responsive Smiling (smiles occurring within 1-second of partner’s smile, controlling for overall level of infant and parent smiling). ASD diagnosis occurred at 36 months based on results from gold-standard autism diagnostic measures and clinical judgment. Children were divided into three groups: Low-Risk (n=24), High-Risk/No ASD (n=31), and ASD (n=9). 

Results:  Diagnostic group differences in parent and infant smiling variables were assessed by conducting a series of one-way ANOVAs. There were no diagnostic group differences in either of the parent smiling variables, suggesting that parents of high- and low-risk children smile at comparable levels and are similarly responsive during interactions with their infants. There were, however, differences between diagnosis groups in infant smiling behaviors. While there was no difference in the overall frequency of infant smiling, there was a group difference in contingent responsive smiling, F(2,61)=3.58, p=.03. Post hoc analyses revealed a significant difference between the High-Risk/No ASD (M=.08, SD=.08) and Low-Risk (M=.13, SD=.08) groups, p=.04. The ASD group did not significantly differ from either group. 

Conclusions:  This is one of the first studies to utilize a micro-coding approach to examine infant responsive social smiling in relation to autism risk. Interestingly, the overall level of infant smiling did not differ by infant risk group or eventual diagnosis; rather, responding to another’s smile within a 1-second window differentiated the infants with a family history of ASD from typically developing controls. Infants eventually diagnosed with ASD did not differ from unaffected children on either smiling variable. Although it is difficult to interpret these results given the small number of diagnosed children in our sample, this suggests that responsive social smiling may represent an endophenotype related to genetic risk for ASD, rather than a specific risk factor for the disorder.