Rhythm is a timescale

Many studies in the linguistic literature have tried to explain the rhythmic component of speech by resorting to the notion of isochrony. The problems with such approaches have been demonstrated in various recent works, owing to the fact that natural speech is highly irregular and quasi-periodic at best. Rhythm also plays a role in the link between brain oscillations and linguistic constituents, where entrainment is often assumed to be the underlying mechanism. Here too, the non-isochronous nature of the speech signal led recent works to call for a more nuanced understanding of entrainment in the context of language. We suggest that rhythm is the timescale within which temporal relationships between isolated events are perceived (about 0.5–12 Hz). Moreover, we argue that isochrony is not what defines rhythm – it is one of the goals that rhythm can achieve. In music, isochrony often characterizes the signal shared between listeners, to promote phase-locking to external sources. In speech, however, isochrony needs to be sourced from internal time-keeping mechanisms, since it is likely the baseline measurement for mental representations, allowing us to perceive the dynamic timing patterns in speech rate, which, in turn, enrich and facilitate comprehension via prosody.