Rhythm Across Species: Situating Human Speech in a Comparative Framework.

At the level of smaller linguistic units, such as words and syllables, rhythm is characterized by a high degree of heterogeneity between languages. This suggests that it is distinct from nonhuman animal communication, where underlying isochrony is often observed. In this study, we examine speech rhythm using units similar to those previously examined for nonhuman animals: interonset intervals (IOIs), that is, sound elements surrounded by silence. Surprisingly, IOI durations are relatively similar across a comprehensive sample of 48 languages from all inhabited continents, with a median of approximately 2 s. IOI beats are also relatively similar at around 0.5 Hz, and human speech fits between exemplary animal species in terms of rhythmic variability and beat precision, that is, the extent to which an isochronous beat model fits the sequence. By revealing cross-linguistic regularities and comparing them to those of other animal species, our results help to position human speech within the broader spectrum of rhythmic vocal behavior observed in nature.