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The role of envelope tACS in modulating speech comprehension and listening effort in post-stroke receptive aphasia
Poster Session A, Wednesday, September 30, 11:00 am - 1:00 pm, Wangari Maathai
This poster is part of the Sandbox Series.
Rongru Chen1, Emily Upton1, Teresa Hu1, Carol Atta1, Matt Davis2, Holly Robson1; 1University College London (UCL), 2University of Cambridge
Background. The speech envelope is critical for speech intelligibility (Rosen, 1992; Shannon et al., 1995). Neuro-oscillatory models propose that envelope fluctuations regulate the timing of neural activity, supporting speech parsing and enhancing sensory sensitivity (Ghitza, 2012; Giraud & Poeppel, 2012). In typical listeners, neural activity synchronises with envelope fluctuations, particularly when speech is degraded. In people with post-stroke aphasia, however, envelope tracking can be reduced, especially following lesions to the left superior temporal lobe (De Clercq et al., 2025). Notably, the capacity to time-lock to the speech envelope positively correlates with comprehension success in aphasia patients with left temporal lesions (Mai et al., 2025). Transcranial alternating current stimulation (tACS) in the shape of the speech envelope has been shown to modulate speech perception in typical listeners (Wilsch et al., 2018). However, the effect of tACS depends on the phase relationship between the tACS waveform and the speech envelope (Zoefel et al., 2018). In this study, we will examine whether envelope tACS can enhance speech comprehension and reduce listening effort in people with post-stroke receptive aphasia. We hypothesise that (1) speech comprehension will be enhanced and listening effort will be reduced during optimum-phase tACS relative to sham, and (2) both measures will be phasically modulated by the tACS–speech phase relationship. Methods. We aim to recruit 12 adults with chronic post-stroke receptive aphasia, based on a power analysis indicating 80% power to detect within-participant effects using data from Wilsch et al. (2018). Participants will complete a sentence-comprehension task. Each sentence comprises three coordinated active declarative clauses with a shared subject and an omitted final word. On each trial, participants will select, from six pictures, the image corresponding to the missing word. Envelope tACS will be delivered via electrodes over the bilateral auditory cortices (T7 and T8), with two return electrodes positioned to the left and right of Cz according to the International 10–10 system. The stimulation waveform will be derived from the envelope of the simultaneously presented sentence. It will then be delayed with respect to the speech signal by a fixed latency of 150 ms and shifted to one of the four phase conditions: 0°, 90°, 180°, or 270°. Sentence sets will be balanced for cloze predictability and final-word frequency and mapped to phase conditions across participants using a Latin-square design. Sentences will be pseudorandomised across phase conditions and presented during active and sham stimulation in a double-blind, within-participant design. Analysis. The primary outcome will be sentence-comprehension accuracy. Pupil dilation will provide a secondary index of listening effort; blink rate and reaction time will be additional measures. For Hypothesis 1, each participant's optimum tACS set will be compared with both their optimum sham set and the item-matched sham set. Participant-level contrasts will then be tested against zero. For Hypothesis 2, single-trial regression with sine- and cosine-transformed phase predictors will test whether performance varies sinusoidally with stimulation phase. Participant-level results will be combined using Fisher's method (Zoefel et al., 2019). Data collection is ongoing.
Topic Areas: Speech Perception, Disorders: Acquired