Speech onsets and sustained speech contribute differentially to delta and theta speech tracking in auditory cortex

Abstract

When we attentively listen to an individual’s speech, our brain activity dynamically aligns to the incoming acoustic input at multiple timescales. Although this systematic alignment between ongoing brain activity and speech in auditory brain areas is well established, the acoustic events that drive this phase-locking are not fully understood. Here, we use magnetoencephalographic recordings of 24 human participants (12 females) while they were listening to a 1 h story. We show that whereas speech–brain coupling is associated with sustained acoustic fluctuations in the speech envelope in the theta-frequency range (4–7 Hz), speech tracking in the low-frequency delta (below 1 Hz) was strongest around onsets of speech, like the beginning of a sentence. Crucially, delta tracking in bilateral auditory areas was not sustained after onsets, proposing a delta tracking during continuous speech perception that is driven by speech onsets. We conclude that both onsets and sustained components of speech contribute differentially to speech tracking in delta- and theta-frequency bands, orchestrating sampling of continuous speech. Thus, our results suggest a temporal dissociation of acoustically driven oscillatory activity in auditory areas during speech tracking, providing valuable implications for orchestration of speech tracking at multiple time scales.

Dissociating endogenous and exogenous delta activity during natural speech comprehension

“…We confirmed that temporally manipulating prosodic cues compromises cortical alignment to speech, specifically in bilateral auditory areas in the delta frequency band (Fig 2A-B). This replicates previous EEG findings [39], aligns with a proposed role of delta oscillations in temporal expectations [55,56] and is consistent with previous speech-brain coupling research proposing delta activity specific to speech onsets [23]. In this line, we foster the notion that delta speech-brain coupling reflects top-down predictive processes [15] evoked by acoustical regularities [57,58]; in particular the temporal structure of pauses [46].…”

“…While memory limits constrain chunk duration and thus necessitate occasional segmentation, each chunk-size filling of the buffer is coherent through the inter-word dependencies—thus allowing for the integration of word meanings within the chunk, and thus comprehension [43]. Previously, invasive work has shown that a spatially distinct area within superior temporal gyrus is exclusively sensitive to speech onsets [51] while non-invasive recordings demonstrated that delta speech-brain coupling is specific – and temporally restricted - to speech onsets [23]. However, it is not yet clear whether contextually-driven onsets (such as the boundaries of multi-word chunks) are sufficient to align activity on longer time-scales during listening.…”

Assessing real-world music listening in concerts

“…Here, the acoustic signal is reduced to an overall feature that best represents the auditory stimulus. The envelope and/or its derivative has been a strong candidate as a way to capture overall capture naturalistic speech (Chalas et al, 2023) and music (Di Liberto et al, 2020;Dmochowski et al, 2012;Hausfeld et al, 2021;Kaneshiro et al, 2020;Weineck et al, 2022).…”

“…Such investigations have been conducted in brain oscillations (Chalas et al, 2023;Harding et al, 2019;Kaneshiro et al, 2020;Peelle et al, 2013;Vanden Bosch der Nederlanden et al, 2020); thought questions remain to what extent this could apply also to peripheral rhythms (Criscuolo et al, 2022;Klimesch, 2018;Parviainen et al, 2022).…”

“…Consequently, other methods might still prove useful in assessing peripheral and neural responses in naturalistic stimuli. Indeed, there are several exciting new methods that are being developed to assess responses to naturalistic stimuli, such as mutual information (Chalas et al, 2023) and temporal-response-functions (Di Liberto et al, 2020;Kern et al, 2022;Weineck et al, 2022).…”