Interpersonal Synchrony During a Client-Therapist Role-Play Interaction: The Role of Modalities, Facets, and Relational Context

Interpersonal synchrony (IS), the temporal coordination between individuals during interaction, is a complex phenomenon that manifests across different modalities (e.g., behavioral and physiological) and coordination facets (e.g., strength and flexibility). In psychotherapy, IS is increasingly considered a potential embodied marker of the client-therapist relationship. However, little is known about how relational context shapes IS coordination patterns, or how they relate to perceived relationship quality. This study aimed to identify IS coordination patterns associated with two relational contexts (emotion-focused vs. solution-focused conversations) and to examine how these patterns relate to subjective perceptions of the client-therapist relationship. 168 psychology students (84 dyads) participated in two consecutive 13-min client-therapist role-play conversations with different goals: exploring emotions (emotion-focused) and brainstorming solutions (solution-focused). Windowed Cross-Lagged Correlation was used to quantify IS from upper-body movement (using Motion Energy Analysis), high-frequency heart rate variability, and electrodermal activity (average and slope). For each modality, six IS facets were extracted, representing three facet families: strength, flexibility, and leading-following dynamics. IS was above chance level across all modalities and facets in both conditions (ds ≈0.26-1.09). Although the context manipulation was effective at a subjective level, no condition differences in IS were observed after correction for multiple testing. Analyses accounting for dyads' interaction history (i.e., sequence of conditions) revealed context-dependent effects in two modalities: movement strength and EDA_Slope leading-following dominance. Both modalities were also related with the perceived emotional bond, but not with perceived collaboration, and these associations varied as a function of relational context. These findings suggest that contextual factors, including conversation goals and dyadic history shape coordination dynamics. Implications for modality and facet selection, and context manipulation in IS research are discussed.