How Interpersonal Coordination Affects Individual Behavior (and Vice Versa): Experimental Analysis and Adaptive HKB Model of Social Memory

How one behaves after interacting with a friend may not be the same as before the interaction. The present study investigated which spontaneous coordination patterns formed between 2 persons and whether a remnant of the interaction remained (“social memory”). Pairs of people sat face-to-face and continuously flexed index fingers while vision between partners was manipulated to allow or prevent information exchange. Trials consisted of 3 successive 20-s intervals: without vision, with vision, and again without vision. Steady, transient, or absent phase coupling was observed during vision. In support of social memory, participants tended to remain near each other's movement frequency after the interaction ended. Furthermore, the greater the stability of interpersonal coordination, the more similar partners' postinteractional frequencies became. Proposing that social memory resulted from prior frequency adaptation, a model based on Haken–Kelso–Bunz (HKB) oscillators reproduced the experimental findings, even for patterns observed on individual trials. Parametric manipulations revealed multiple routes to social memory through the interplay of adaptation and other model parameters. The experimental results, model, and interpretation motivate potential future research and therapeutic applications.