The synchronization of physical movements between organisms is critical to exercising one's influence on peers, initiating social learning, establishing group solidarity, and even facilitating pro-social behaviour [1,2,3,4]. Indeed, this behavioural synchrony maintains a distinct social importance, as it functions like a "social glue" that helps to solidify relationships between both humans and animals. further posited that this coordination is a visible manifestation of dyadic rapport development, and subsequent research supports their prediction [6,7]. Because situational conditions impact rapport-development between partners [8], it is plausible that subsequent displays of synchrony might be concurrently affected; accordingly, our investigation sought to explore how contextual and participant characteristics influence this rapport / synchrony interplay.Grahe and Sherman [8] proposed that altering perceptions of dyadic responsibility during a mutual task affected communication between both dyad members; unsurprisingly, these subsequent changes to communication efforts might then influence self-reported feelings of rapport [9,10]. More specifically, Dunbar's [9] dyadic power theory posits that as an individual's perception of responsibility increases, their likelihood of communicating using dominant behavior is subsequently heightened. Dominant communication displays hinder rapportbuilding, and thus Study 1 examined how perceptions of authority and the gender-specificity of an interdependent task (as gender scripts magnify self perceptions of social power [11]) influenced rapport development and nonverbal coordination.As mentioned above, gender socialization encourages men and women to rely on different nonverbal communication tendencies [12,13], and these tendencies may encourage or impede rapport development. For example, physical manifestations of positivity and attentiveness (two elements of Tickle-Degnen and Rosenthal's [5] theorized rapport construct) are more often observed in female same-sex dyads than in male-male pairings [14]. Women also appear more sensitive to rapport-facilitating actions when making judgments about dyadic exchanges [15]. Study 2 sought to determine if a dyad's sex makeup