How Emotion Contagion Changes as Strangers Become Acquainted: A Longitudinal Conversation Study

People’s emotional states often become more similar after social interactions, a process known as emotion contagion. Emotion contagion is considered both a by-product of shared goals and a tool for strengthening social bonds. Although cross-sectional evidence suggests emotion contagion is positively related to bond strength, few studies have investigated this relationship longitudinally as people become acquainted. Perhaps emotion contagion increases as people become closer (a within-dyad effect), reflecting relationship closeness. Or perhaps some dyads have a stable mutual liking and a tendency towards emotion contagion that does not change over time (a between-dyad effect). Our study disentangled these two accounts. Pairs of unacquainted participants had conversations weekly for six weeks over Zoom. Participants reported pre- and post-conversation emotion states and closeness to their partner after each conversation. Emotion contagion, measured in three different ways, declined over time as dyads became interpersonally closer (evidence for a within-dyad effect). This decline may indicate increased comfort with emotional divergence. Notably, dyads that reported greater average interpersonal closeness exhibited larger changes in emotion states during their conversations, aligning with previous between-dyad findings. Thus, the association between emotion contagion and feelings of interpersonal closeness depends on whether we consider change within a dyad or compare between dyads.