Social origins of rhythm? Synchrony and temporal regularity in human vocalization

Humans have a capacity to perceive and synchronize with rhythms. This is unusual in that only a minority of other species exhibit similar behavior. Study of synchronizing species (particularly anurans and insects) suggests that simultaneous signal production by different individuals may play a critical role in the development of regular temporal signaling. Accordingly, we investigated the link between simultaneous signal production and temporal regularity in our own species. Specifically, we asked whether inter-individual synchronization of a behavior that is typically irregular in time, speech, could lead to evenly-paced or "isochronous" temporal patterns. Participants read nonsense phrases aloud with and without partners, and we found that synchronous reading resulted in greater regularity of durational intervals between words. Comparison of same-gender pairings showed that males and females were able to synchronize their temporal speech patterns with equal skill. These results demonstrate that the shared goal of synchronization can lead to the development of temporal regularity in vocalizations, suggesting that the origins of musical rhythm may lie in cooperative social interaction rather than in sexual selection.