Smiling in Infants with and without ASD during Infant-Caregiver Face-to-Face Interactions

Background: Disrupted social engagement is a core feature of autism spectrum disorders (ASD). Individuals with ASD, even intellectually capable adults, have markedly impaired reciprocal social interaction abilities, displaying reduced eye-contact and difficulty using non-verbal cues. By contrast, typically-developing (TD) infants exhibit remarkable sensitivity to social contingencies present in face-to-face interactions very early in development. By approximately 2 months of age, TD infants are already active participants in dyadic interactions and engage in “social smiling”: smiles that are linked to vocalizations and affective changes in caregivers. The emergence of social smiling and sensitivity to contingencies between one’s own behavior and the behavior of an interactive partner may mark a pivotal moment in infant development, as success in reciprocal social interaction likely plays a key role in shaping future social and communicative outcomes. Consequently, examining smiling early in life may not only provide an early diagnostic marker of ASD, but may also inform how early deviation from the normative course of social development impacts the unfolding of social deficits characteristic of ASD.

Objectives: This study investigates whether TD infants and infants who later receive a diagnosis of ASD differ in: (1) frequency and duration of smiles; and (2) contextual influences on smiling, namely whether smiles are more likely to be elicited when looking towards versus away from a social partner. 

Methods: Three-to-five-month-old TD infants (n=16; mean age = 4.16 months) and infants who later received a diagnosis of ASD (n=13; mean age = 4.08 months) participated in this study. Using eye-tracking technology, we recorded 30-second face-to-face interactions between the infants and their caregivers.  Infant facial expressions (including smiling), gaze direction, and caregiver facial expressions and vocalizations were coded as in Lavelli & Fogel (2005).  Measures analyzed in the present study include: (1) the proportion of time infants spent smiling; and (2)

the proportion of time infants spent smiling while gazing towards versus away from their caregivers.

Results: Analyses revealed a marginally significant interaction (p = .07) between diagnostic group and gaze direction while smiling. Follow-up analyses showed that TD infants spent significantly more time smiling when looking at their caregivers’ faces than when looking away (p = .004). By contrast, infants with ASD showed no difference in time spent smiling while looking at their caregivers’ faces versus looking away (p=.629).

Conclusions: Results indicate that smiling in TD infants is modulated by social context, with smiles occurring more frequently when gazing at caregivers. This suggests that smiling in TD infants may reflect emotional engagement directed towards a social partner. Conversely, smiling behavior in infants with ASD was not modulated by social context, as they were equally likely to smile when gazing away from and towards their caregivers. These results highlight atypicalities in social smiling, which are likely indicative of an early disruption in typical processes of social development. Future directions include continuing these analyses in a larger sample and examining additional measures of sensitivity to social contingencies during face-to-face interactions.