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

ABSTRACT

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.

Acknowledgments

We appreciate valuable input from Guillaume Dumas, Gonzalo de Guzman, Karl Lerud, and Leonardo Rhodes. We thank the anonymous reviewers for their suggestions that greatly improved the manuscript.

Notes

¹ No special significance is attached here to the words “social” or “social memory” beyond the fact that the present research quantitatively studies the interaction between two human beings and the consequences on each individual's behavior after the interaction is over.

² A possible evolutionary advantage of social memory is that maintaining a restricted range of frequencies facilitates initiating future interactions because having similar dispositions increases the probability of coordination in the future. Such coordination may take the form of cooperation or competition (Kelso & Engstrøm, 2006).

³ Although it is possible that some participants intended to coordinate on some trials, for the most part it seems unlikely on empirical grounds. When participants are asked to intentionally coordinate in-phase and anti-phase, the distributions of relative phase are very different (e.g., Naeem, Prasad, Watson, & Kelso, 2012) than the distributions shown here for the spontaneous case. A signature of truly spontaneous coordination seems to be bistability in-phase and anti-phase, which several pairs showed in a sustained manner, and most showed in an intermittent manner.

Additional information

Funding

This work was supported by the Chaire d'Excellence Pierre de Fermat, the National Institute of Mental Health (MH080838), and the Davimos Family Endowment for Excellence in Science.