Cortical tracking of speech and stuttering (Gastaldon et al., 2024)

Purpose: The purpose of this study was to investigate cortical tracking of speech (CTS) in adults who stutter (AWS) compared to typically fluent adults (TFAs) to test the involvement of the speech-motor network in tracking rhythmic speech information.

Method: Participants’ electroencephalogram was recorded while they simply listened to sentences (listening only) or completed them by naming a picture (listening for speaking), thus manipulating the upcoming involvement of speech production. We analyzed speech–brain coherence and brain connectivity during listening.

Results: During the listening-for-speaking task, AWS exhibited reduced CTS in the 3- to 5-Hz range (theta), corresponding to the syllabic rhythm. The effect was localized in the left inferior parietal and right pre/supplementary motor regions. Connectivity analyses revealed that TFAs had stronger information transfer in the theta range in both tasks in fronto-temporo-parietal regions. When considering the whole sample of participants, increased connectivity from the right superior temporal cortex to the left sensorimotor cortex was correlated with faster naming times in the listening-for-speaking task.

Conclusions: Atypical speech-motor functioning in stuttering impacts speech perception, especially in situations requiring articulatory alertness. The involvement of frontal and (pre)motor regions in CTS in TFAs is highlighted. Further investigation is needed into speech perception in individuals with speech-motor deficits, especially when smooth transitioning between listening and speaking is required, such as in real-life conversational settings.

Supplemental Material S1. Source-level CTS in the listening-only task. No statistically significant differences were found.

Supplemental Material S2. Spectral characteristics of the speech envelope. We computed the power spectrum of the speech envelope for the frequencies that phase-synchronized with the electrophysiological brain activity (i.e., < 10 Hz). The more prominent amplitude modulations were between 3 and 4 Hz, as expected from previous studies (Park et al., 2015; Lizarazu et al., 2019).

Supplemental Material S3. Scatterplot of the correlation between right STG → left SM and SSI in AWS. Although statistically not significant, a negative trend is observable whereby reduced connectivity from the right STG to the left SM cortex is associated with higher SSI-4 scores (Stuttering Severity Instrument 4; Riley, 2009).

Supplemental Material S4. Correlations between the neural measures found to be different across groups in the listening-for-speaking task (coherence at sensor and source level, connectivity at theta) and behavioral measures (response times and SSI-4). Separate correlations for AWS and TFA are reported only as exploratory.

Supplemental Material S5. Number of EEG data segments considered for CTS and connectivity analyses from the different task conditions and constraint levels in both groups (see original experimental paradigm in Gastaldon et al., 2023, and Materials and Methods in the main text for further explanation). Mean ± standard deviation in brackets. Statistics show that there are no differences between groups in either task in the number of data segments.

Gastaldon, S., Busan, P., Molinaro, N., & Lizarazu, M. (2024). Cortical tracking of speech is reduced in adults who stutter when listening for speaking. Journal of Speech, Language, and Hearing Research, 67(11), 4339–4357. https://doi.org/10.1044/2024_JSLHR-24-00227