A universal of speech timing: Intonation units form low frequency rhythms and balance cross-linguistic syllable rate variability

Intonation units (IUs) are a universal building-block of human speech. They are found cross-linguistically and are tied to important language functions such as the pacing of information in discourse and swift turn-taking. We study the rate of IUs in 48 languages from every continent and from 27 distinct language families. Using a novel analytic method to annotate natural speech recordings, we identify a low-frequency rate of IUs across the sample, with a peak at 0.6 Hz, and little variation between sexes or across the life span. We find that IU rate is only weakly related to speech rate quantified at the syllable level (SR), and crucially, that cross-linguistic variation in IU rate is smaller than cross-linguistic variation in SR. Since SR was shown to be inversely related to information density quantified at the syllable level, we suggest that across languages, IUs are more balanced than syllables in their information content.