Individual Differences in Speech Monitoring: Functional and Structural Correlates of Delayed Auditory Feedback

Speech production relies on continuous self-monitoring to ensure that produced sounds match intended targets. Delayed auditory feedback (DAF) disrupts speech fluency by perturbing this alignment and offers a powerful tool to study the sensorimotor control of speech. Here, we combined functional and diffusion-weighted MRI in 31 participants producing words with and without DAF. Participants showed substantial variability in how much their speech slowed under DAF, quantified by a continuous susceptibility index (SI). At the group level, DAF elicited increased activation in a right-lateralized speech motor network encompassing the superior temporal, supramarginal, inferior frontal, precentral, and supplementary motor areas, along with engagement of the left cerebellum. In contrast, individual differences revealed the opposite pattern: higher susceptibility was associated with stronger activation in left-hemisphere speech motor homologues. Diffusion analyses of the arcuate fasciculus (AF) further showed that greater fiber density in the right posterior AF predicted lower susceptibility, whereas larger right long AF volume predicted higher susceptibility. Together, these findings identify a lateralized and tract-specific organization of speech monitoring: fluency under perturbation depends on a right-lateralized monitoring network that supports integration of auditory and somatosensory feedback through the right posterior AF, while stronger auditory–motor coupling via the right long AF and excessive left-hemisphere activation predict greater vulnerability to feedback disruption.