Shared Duration of Speech Intervals Across 49 Human Languages

Research on speech rhythm has predominantly focused on smaller linguistic units such as syllables and words. At these levels, rhythm is characterized by a high degree of heterogeneity between languages, suggesting that it is intrinsically distinct from nonhuman animal communication, where the underlying isochrony is frequently observed. In this study, we investigate speech rhythm based on units similar to those used in work on nonhuman animals, i.e., sound elements surrounded by silence. Interval durations are surprisingly similar between a comprehensive sample of 49 languages from all inhabited continents, with a median of ∼2 seconds. This pattern is independent of gender, age, or language-specific factors. IOI beats are also very similar, at around 0.5 Hz, but isochronous beat models are not a good fit for human speech compared to those of other animal species. By revealing cross-linguistic regularities alongside a lack of isochrony, our results help to place human speech within the wider spectrum of rhythmic strategies observed in nature.