The forms and mechanisms of body motion synchrony in conversation

When people converse, they communicate not only through their words, but also through other modalities, including the ways they move their bodies. Prior research suggests that people’s body movements may synchronize during conversation. However, the definitions of synchrony, parts of the body, types of interactions, and sizes and social characteristics of the samples in these prior studies are highly heterogeneous. This investigation draws on markerless pose estimation and a large dataset of conversing friends and strangers to answer two key questions: how, precisely, do people’s bodies synchronize during conversation, and what mechanisms produce these forms of synchrony? We observe strong evidence for three separable forms of synchrony –synchrony in the amount of motion of interacting pairs, amount of motion in non-interacting pairs, and of motion of interacting pairs – each of which differs between friends and strangers. We then identify four putative mechanisms – entrainment to conversational conventions, turn-taking related motion, proxemic distance maintenance, and conservation of motion across the dyad – that can account for these forms of synchrony and the differences between friends and strangers. These findings illuminate the heterogeneity of conversational synchrony, and the mechanisms thereof. This paves the way for identifying clearer relationships between synchrony and high-level social-affective constructs.