Neural Entrainment to Speech Modulates Speech Intelligibility

TLDR

Speech is essential for communication, and speech‑brain entrainment—neural alignment to the acoustic envelope—is a ubiquitous mechanism linked to speech intelligibility. The study aims to determine whether speech‑brain entrainment causally influences speech intelligibility rather than merely reflecting it. The authors used transcranial current stimulation shaped by the speech envelope to selectively modulate neural entrainment while keeping acoustic and task conditions constant. Both experiments show that modulating entrainment improves speech recognition, confirming a causal role of speech‑brain entrainment and suggesting transcranial envelope‑shaped currents could enhance comprehension in difficult listening conditions.

Abstract

Speech is crucial for communication in everyday life. Speech-brain entrainment, the alignment of neural activity to the slow temporal fluctuations (envelope) of acoustic speech input, is a ubiquitous element of current theories of speech processing. Associations between speech-brain entrainment and acoustic speech signal, listening task, and speech intelligibility have been observed repeatedly. However, a methodological bottleneck has prevented so far clarifying whether speech-brain entrainment contributes functionally to (i.e., causes) speech intelligibility or is merely an epiphenomenon of it. To address this long-standing issue, we experimentally manipulated speech-brain entrainment without concomitant acoustic and task-related variations, using a brain stimulation approach that enables modulating listeners' neural activity with transcranial currents carrying speech-envelope information. Results from two experiments involving a cocktail-party-like scenario and a listening situation devoid of aural speech-amplitude envelope input reveal consistent effects on listeners' speech-recognition performance, demonstrating a causal role of speech-brain entrainment in speech intelligibility. Our findings imply that speech-brain entrainment is critical for auditory speech comprehension and suggest that transcranial stimulation with speech-envelope-shaped currents can be utilized to modulate speech comprehension in impaired listening conditions.