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Differences in the timing of action preparation in people who stutter
Poster Session B, Friday, September 12, 4:30 - 6:00 pm, Field House
Irene Echeverria Altuna1,2, Birtan Demirel1, Sage Boettcher1, Kia Nobre1,2, Kate Watkins1; 1University of Oxford, 2Yale University
Stuttering involves interruptions to the smooth flow of speech. Accordingly, speech fluency can be induced in people who stutter using external cues to time speech production. From this and related observations, stuttering has been proposed to be related to differences in the internal timing of speech. Recent studies have reliably shown differences in people who stutter in mu/beta (8-30 Hz) frequency M/EEG (magnetoencephalography and electroencephalography) activity patterns prior to speech production. Whether this difference is speech-specific or reflects a more general anomaly in motor control remains unknown. Also uncharted is the extent to which the temporal coordination of action preparation is affected in people who stutter. Here, we developed a working-memory task in which participants shifted between hand-action plans as a function of internally driven temporal expectations. Participants held the orientation of two tilted bars, each linked to an action (left or right button press) in working memory. At the end of each trial, participants were probed to report the orientation of one of the bars. In most trials (80%), an informative retro-cue prompted participants to prioritize one visual item and its associated action plan. In half of those trials, participants were probed to report the orientation of the cued item following a short delay (1 s). In the other half, the delay between the cue and the probe was long (3 s) and participants were probed about the opposite (uncued) item. In this task, the passage of time prompted participants to shift their focus from the cued item to the other item and associated response plan. The dynamic prioritisation of action plans was mirrored by an action-specific and temporally tuned lateralised modulation of mu/beta (8-30 Hz) frequency activity as measured using MEG in both people who stutter (n = 20) and typically fluent speakers (n = 20). Source-reconstruction of the MEG signal localised the lateralised mu/beta modulation to the primary motor cortex (M1). Intriguingly, people who stutter differed from typically fluent speakers in the temporal pattern of mu/beta activity modulation when shifting between action plans. Specifically, lateralised mu/beta activity modulation was weaker in people who stutter relative to typically fluent speakers around the time of shift between action plans. In contrast, lateralised mu/beta activity modulation was similar in both groups during the later part of the delay, as participants prepared to respond in long trials. While people who stutter were less accurate in their orientation reports than typically fluent speakers in all conditions, we observed no difference in reaction time between the groups. The weakened lateralised mu/beta modulation around shift time in people who stutter may reflect differences in action preparation under uncertainty. It could also reflect differences in the temporal coordination of action preparation. Furthermore, the observed differences in manual action preparation between the groups indicate that stuttering may be linked to differences in action preparation across several motor systems.
Topic Areas: Speech Motor Control,