Cardiac dynamics during social evaluative feedback: Evidence from intersubject representational similarity analysis.

In everyday interactions, social evaluative feedback can elicit defensive responses that vary across individuals, underscoring the need to clarify the psychophysiological mechanisms underlying this variability. This study examined the cardiac correlates of defensive responses to social feedback, focusing on how cardiac activity reflects individual differences in self-protective behavior. Participants completed a mobile-based reciprocal artwork evaluation task while cardiac activity was continuously monitored via photoplethysmography using a wearable smartwatch. During the task, participants received positive, negative, or neutral feedback from partners and subsequently evaluated the creativity of the partner's artwork, indexing defensive behavioral responses. Feedback-evoked heart rate responses were analyzed using temporal intersubject representational similarity analysis (IS-RSA) to assess how dynamic cardiac similarity patterns related to individual differences in behavioral tendencies across feedback conditions. Results revealed that social feedback systematically influenced subsequent evaluations of the partner's artwork. Negative feedback elicited transient heart rate deceleration, whose magnitude was inversely associated with resting heart rate variability. IS-RSA further revealed that individuals who made more favorable judgments following positive feedback exhibited greater intersubject cardiac similarity during the early post-feedback period. Follow-up group analyses indicated that this convergence reflected transient heart rate deceleration among individuals with stronger behavioral bias. Together, these findings elucidate the physiological basis of self-protective bias in social contexts and highlight the role of individual psychophysiological variability.