Synchronized tapping as a model of minimal social interaction

Human beings have an extraordinary ability to synchronize their actions, goals, and intentions in order to accomplish goal-directed tasks. In order to study the dynamics and mechanisms involved in entrainment in social interaction, a finger tapping experiment was carried out, where pairs of subjects were asked to tap on their respective keyboards following an 8-beat stimulus sent through their headphones. The subjects were instructed to keep the given beat as well as synchronize with the ‘other’. They were in scenarios where they could either hear themselves tapping, the other, or the computer metronome. Analysis of their inter-tap intervals (ITI) suggests that dyads are unable to achieve full synchrony but rather adopt oscillatory behaviour, such that each member attempts to lock in phase with the other, thereby error-correcting their tapping onsets in opposite directions. Windowed cross-correlograms showed that there was no leader/follower in the interactive condition, revealing high correlation in both lag +1 and -1, which suggested shared continuous adaptation to the other’s output. A dynamical systems approach was taken to model this behaviour, using a system of two oscillators coupled in both phase and frequency, corresponding to phase and period error correction.