Intonation Units in spontaneous speech evoke a neural response

Abstract

Spontaneous speech is produced in chunks called Intonation Units (IUs). IUs are defined by a set of prosodic cues and occur in all human languages. Linguistic theory suggests that IUs pace the flow of information and serve as a window onto the dynamic focus of attention in speech processing. IUs provide a promising and hitherto unexplored theoretical framework for studying the neural mechanisms of communication, thanks to their universality and their consistent temporal structure across different grammatical and socio-cultural conditions. In this article, we identify a neural response unique to the boundary defined by the IU. We measured the EEG of participants who listened to different speakers recounting an emotional life event. We analyzed the speech stimuli linguistically, and modeled the EEG response at word offset using a GLM approach. We find that the EEG response to IU-final words differs from the response to IU-nonfinal words when acoustic boundary strength is held constant. To the best of our knowledge, this is the first time this is demonstrated in spontaneous speech under naturalistic listening conditions, and under a theoretical framework that connects the prosodic chunking of speech, on the one hand, with the flow of information during communication, on the other. Finally, we relate our findings to the body of research on rhythmic brain mechanism in speech processing by comparing the topographical distributions of neural speech tracking in model-predicted and empirical EEG. This qualitative comparison suggests that IU-related neural activity contributes to the previously characterized delta-band neural speech tracking.

Speech Prosody Serves Temporal Prediction of Language via Contextual Entrainment

“…These features need to exhibit sufficient rhythmicity to facilitate conversational entrainment. Although ubiquitous rhythmicity is not characteristic of human speech, previous research has demonstrated that speech is rhythmic enough on the prosodic level to trigger entrainment in dialog ( Inbar et al, 2020 ; Stehwien and Meyer, 2021 ); furthermore, rhythmic intonational units in speech evoke a neural response ( Inbar et al, 2023 ). Further research quantifying the rhythmicity of naturalistic speech and investigating the differences in prosodic entrainment for rhythmic and nonrhythmic parts could provide additional evidence for this claim.…”

Neural and behavioural rhythmic tracking during language acquisition: The story so far

“…It fails to consider the role of other features contained in the speech signal, such as phonetic features, formant transitions, temporal fine structure, etc. Inbar et al (2023) recently investigated the neurophysiological basis of Intonation Units (IU), a fundamental unit of human languages (Inbar et al, 2020). In their naturalistic listening study using EEG, Inbar et al ( 2023) demonstrated robust evoked responses to IU in adult listeners.…”

Dissociating endogenous and exogenous delta activity during natural speech comprehension

“…However, on the timescale of word groups such an alignment between acoustic components, linguistic elements and brain activity is not clearly evident. One prominent example are prosodic phrases, which exhibit rhythmicity in the scale of ~1 s [18,19] and are proposed to be tracked accordingly by an acoustically-driven oscillator (in the delta range; below 2 Hz; [20][21][22]). Acoustic -and prosodic -landmarks, speech pauses, have been also related to speech-brain alignment in the delta frequency band [23].…”