Affect synchrony and emotion coregulation are separable processes: Evaluation of relational stress and mother-infant synchrony.

Establishing and repairing ruptures in mother-infant positive affect synchrony are thought to support infants' self-regulation and social competence. Yet, despite rich theorizing, little is known about associations between mother-infant positive affect synchrony and emotion coregulation. This study used the Still Face Paradigm (SFP), which consists of separate initial play, Still Face (SF) stressor, and reunion phases, to assess levels and changes of within-dyad synchrony before and after an experimentally induced relational stressor in a sample of 77 mother-infant (M = 5.6 months; 53% female) dyads. We hypothesized that, on average, dyads would exhibit positive affect synchrony before and after the SF and that within-dyad affect synchrony would increase following the SF. Guided by biobehavioral synchrony and mutual regulation models, we also hypothesized that post-SF increases in synchrony and greater post-SF synchrony would be associated with greater infant negative affect reactivity and recovery. Infant negative affect and infant and maternal positive affect were coded in 3-s epochs for each phase of the Still Face Paradigm. Analyses used residual dynamic structural equation modeling, which disentangled mother- and infant-led synchrony, and multilevel regression. Hypotheses regarding typical within-dyad processes were generally supported: Mother-led positive affect synchrony increased from baseline to the poststressor reunion play, and there was evidence of both infant- and mother-led positive affect synchrony during the reunion. Yet, neither infant negative reactivity nor recovery was associated with changes in positive affect synchrony or post-SF levels of synchrony. Results highlight that synchrony is sensitive to relational stress but challenge traditional assumptions that "more" synchrony promotes emotion coregulation. (PsycInfo Database Record (c) 2025 APA, all rights reserved).