Head motion synchrony in unidirectional and bidirectional verbal communication.

Interpersonal communication includes verbal and nonverbal communication. Verbal communication comprises one-way (e.g., a speech or lecture) and interactive verbal communication (e.g., daily conversations or meetings), which we frequently encounter. Nonverbal communication has considerable influence on interpersonal communication, and body motion synchrony is known to be an important factor for successful communication and social interaction. However, most research on body motion synchrony has been elucidated by either the setting of one-way verbal transmission or the verbal interaction setting, and it remains unclear whether verbal directionality and interactivity affect body motion synchrony. One-way and two-way (interactive) verbal communication is implicated in designed or undesigned leader-follower relationships, and also in the complexity and diversity of interpersonal interactions, where two-way verbal communication is more complex and diverse than in the one-way condition. In this study, we tested head motion synchrony between the one-way verbal communication condition (in which the roles of the speaker and listener are fixed) and the two-way verbal communication condition (where the speaker and listener can freely engage in a conversation). Therefore, although no statistically significant difference in synchrony activity (relative frequency) was found, a statistically significant difference was observed in synchrony direction (temporal lead-lag structure as mimicry) and intensity. Specifically, the synchrony direction in two-way verbal communication was close to zero, but this in one-way verbal communication was synchronized with the listener's movement predominantly delayed. Furthermore, synchrony intensity, in terms of the degree of variation in the phase difference distribution, was significantly higher in the one-way verbal communication than in the two-way condition, with bigger time-shifts being observed in the latter. This result suggests that verbal interaction does not affect the overall frequency of head motion synchrony but does affect the temporal lead-lag structure and coherence.