The rise and fall of conversations: Dyads first calibrate and then differentiate using linguistic, facial, and acoustic communication channels

Conversations are dynamic systems of coordinated behavior. Utterances lengthen and shorten, emotions converge and diverge, topics stabilize and vary. Yet the temporal structure of these changes remains uncharacterized. We analyzed 1,656 extended conversations between strangers, using data across linguistic, facial, and acoustic communication channels. Our preregistered analyses tested the temporal trajectories of 27 conversational measures (e.g., utterance length, emotional similarity, topic persistence, acoustic properties). All measures showed quadratic trajectories as predicted, with an initial calibration phase characterized by utterances becoming gradually longer and dyads becoming more semantically and emotionally similar, and these trends subsiding or reversing during a subsequent differentiation phase. This two-phase pattern reliably emerged across multiple communication channels. Conversations with stronger quadratic trajectories in utterance length were associated with greater shared reality between participants. These findings reveal that diverse conversation features may share a common, fundamental temporal structure, part of the hidden choreography underlying human conversation.