Nonverbal Synchrony or Random Coincidence? How to Tell the Difference

Nonverbal synchrony in face-to-face interaction has been studied in numerous empirical investigations focusing on various communication channels. Furthermore, the pervasiveness of synchrony in physics, chemistry and biology adds to its face-validity. This paper is focused on establishing criteria for a statistical evaluation of synchrony in human interaction. When assessing synchrony in any communication context, it is necessary to distinguish genuine synchrony from pseudosynchrony, which may arise due to random coincidence. By using a bootstrap approach, we demonstrate a way to quantify the amount of synchrony that goes beyond random coincidence, thus establishing an objective measure for the phenomenon. Applying this technique to psychotherapy data, we develop a hypothesis-driven empirical evaluation of nonverbal synchrony. The method of surrogate testing in order to control for chance is suitable to any corpus of empirical data and lends itself to better empirically informed