How role reversal and interpersonal closeness shape verbal communication cooperation: an fNIRS hyperscanning study.

Role reversal refers to the exchange of original role responsibilities between interaction partners in social interactions, aiming to achieve perspective shifting and task completion. It plays a crucial role in facilitating interpersonal cooperation. However, research on the neural mechanisms underlying the effects of role reversal on cooperation, particularly under varying interpersonal closeness contexts, remains limited. This study employed hyperscanning technique based on Functional Near-infrared Spectroscopy with a cooperative sorting task to investigate the impact of role reversal and interpersonal closeness on verbal communication cooperation and its neural mechanisms. Our results showed that role reversal not only enhanced cooperative behavior among both friend and stranger dyads but also improved speech fluency in friend dyads, as indicated by faster instructor speech rates and fewer filler words. Furthermore, role reversal significantly increased Inter-brain Synchrony (IBS) among friend dyads, particularly in the bilateral Dorsolateral Prefrontal Cortex, right Pars Triangularis, and right Supramarginal Gyrus. Moreover, we found that role reversal moderated the relationship between IBS in the left Frontopolar and the sorting score, indicating that role reversal can enhance the predictive effect of IBS on cooperative performance. This study provides neural evidence for the interactive effects of role reversal and interpersonal closeness on verbal communication cooperation and reveals the dynamic relationships among behavior, language, and IBS, thereby expanding our understanding of the mechanisms underlying cooperation in natural interactive spoken communication contexts.