Intonation units (IUs) are a fundamental prosodic unit of all known human languages, and as such they likely constitute an absolute universal property of language. IUs are chunks defined by a specific pattern of syllable delivery, together with resets in pitch and articulatory force. In this chapter we discuss IUs from four different perspectives and introduce them within the context of rhythms of speech, language, and the brain. First, we provide a detailed description of how IUs are defined. Second, we review linguistic research on the roles of IUs in communication, including their cross-linguistic applicability. This body of research suggests that IUs provide a universal structural cue for the cognitive dynamics of speech production and comprehension at a timescale of ~1 Hz. Third, we synthesize the linguistic perspective with findings from the study of brain rhythms and cognition. Finally, we review the existing algorithmic tools for IU identification from speech acoustics, to facilitate the incorporation of IUs in experimental and quantitative research.

Recent studies have shown that neural activity tracks the syntactic structure of phrases and sentences in connected speech. This work has sparked intense debate, with some researchers aiming to account for the effect in terms of the overt or imposed prosodic properties of the speech signal. In this chapter, we present four types of arguments against attempts to explain putatively syntactic tracking effects in prosodic terms. The most important limitation of such prosodic accounts is that they are architecturally incomplete, as prosodic information does not arise in speech autonomously. Prosodic and syntactic structure are interrelated, so prosodic cues are informative about the intended syntactic analysis, and syntactic information can be used to aid speech perception. Rather than trying to attribute neural tracking effects exclusively to one linguistic component, we consider it more fruitful to think about ways in which the interaction between the components drives the neural signal.