Glee in threes: Positive affect synchrony in parent-infant triads is moderated by maternal hair cortisol and parenting stress.

Background: Positive affect synchrony, or the reciprocal exchange of positive affect during free play, can scaffold infants' socioemotional development. However, parental stress may compromise the expression and exchange of positive affect within families. The current study assesses whether parenting stress and hair cortisol are associated with positive affect synchrony during a triadic play interaction.

Method: Within 70 different-sex dyads consisting of first-time parents and their six-month-old infants who participated in a four-minute laboratory-based free-play task, facial affect of each member of the triad was observationally microcoded at the second-by-second level. Hair samples were collected from mothers and fathers for cortisol assay, and parents completed a self-report measure of parenting stress.

Results: Using dynamic structural equation modeling (DSEM), we found positive between-level and within-level affect synchrony across all family members, with one exception: infants' affect did not predict fathers' affect at the following timepoint. Mother-to-infant affect synchrony was greater in mothers with higher hair cortisol. Similarly, mothers with higher parenting stress tended to have greater infant-to-mother affect synchrony, and had infants that displayed less overall positive affect across the interaction.

Conclusion: We found evidence for bidirectional, time-lagged synchrony in the momentary positive affect of mothers, fathers, and infants. Maternal hair cortisol concentration and parenting stress seem to increase affect synchrony between mothers and infants- suggesting that parental stress may correlate with greater affective attunement, but less overall positive affect in infants.