Résumé
Because work songs are ubiquitous around the world, singing while working and performing a task with a enactor is presumably beneficial for both joint action and individual task performance. The present study investigated the impact of interpersonal rhythmic vocal interaction on interpersonal phase relations and on individual motor timing performance, which was evaluated by a synchronization-continuation paradigm requiring whole-body movement with or without visual contact. Participants repeated the syllable "tah" or remained silent in a manipulation of vocal interaction, and they were oriented toward or away from their partner to manipulate visual interaction. Results indicated the occurrence of spontaneous interpersonal coordination, evidenced by interpersonal phase relations that were closer to 0 degrees and less variable when participants interacted both visually and vocally. At the individual level, visual interaction increased the variability of synchronization with the metronome but did not modulate the variability of continuation movements, whereas vocal interaction helped to decrease the variability of synchronization and continuation movements. Visual interaction therefore degraded individual movement timing while vocal interaction improved it. Communication via the auditory modality may play a compensatory role in naturalistic contexts where visual contact has potential destabilizing effects.