Speech Movement Variability in People Who Stutter: A Vocal Tract Magnetic Resonance Imaging Study

Abstract

Purpose People who stutter (PWS) have more unstable speech motor systems than people who are typically fluent (PWTF). Here, we used real-time magnetic resonance imaging (MRI) of the vocal tract to assess variability and duration of movements of different articulators in PWS and PWTF during fluent speech production. Method The vocal tracts of 28 adults with moderate to severe stuttering and 20 PWTF were scanned using MRI while repeating simple and complex pseudowords. Midsagittal images of the vocal tract from lips to larynx were reconstructed at 33.3 frames per second. For each participant, we measured the variability and duration of movements across multiple repetitions of the pseudowords in three selected articulators: the lips, tongue body, and velum. Results PWS showed significantly greater speech movement variability than PWTF during fluent repetitions of pseudowords. The group difference was most evident for measurements of lip aperture using these stimuli, as reported previously, but here, we report that movements of the tongue body and velum were also affected during the same utterances. Variability was not affected by phonological complexity. Speech movement variability was unrelated to stuttering severity within the PWS group. PWS also showed longer speech movement durations relative to PWTF for fluent repetitions of multisyllabic pseudowords, and this group difference was even more evident as complexity increased. Conclusions Using real-time MRI of the vocal tract, we found that PWS produced more variable movements than PWTF even during fluent productions of simple pseudowords. PWS also took longer to produce multisyllabic words relative to PWTF, particularly when words were more complex. This indicates general, trait-level differences in the control of the articulators between PWS and PWTF. Supplemental Material https://doi.org/10.23641/asha.14782092

Neural oscillatory activity and connectivity in children who stutter during a non-speech motor task

“…However, given previous results of heightened variability in the timing of movement initiation in both speech and non-speech motor tasks (e.g. Falk et al, 2014; Wiltshire et al, 2021), we expected to see greater variability in response time in the stuttering group. Greater neural variability, indicated by greater trial-by-trial variability in slow oscillatory dynamics (Popovych et al, 2016; Hamel-Thibault et al, 2018), may underlie response time variability.…”

“…Stuttering has been associated with deficits in motor control, particularly for action initiation and timing (Alm et al, 2004; Civier et al, 2013; Chang and Guenther 2020). Besides stuttering events, people who stutter exhibit more variable speech movements compared to people who do not stutter even when their speech is perceptually fluent (e.g., Wiltshire et al, 2021; MacPherson & Smith., 2013; Smith et al, 2012). In non-speech motor tasks, people who stutter often perform slightly worse than people who do not stutter, particularly in demanding tasks that involve complex sequences of movements or fine timing control (e.g., Smith-Bandstra et al 2006ab; Falk et al, 2014; Bauerly and De Nil, 2011; Toyomura et al, 2021), while results have been mixed for simple motor tasks, such as hand claps (Piispala et al, 2016; Hilger et al, 2016; Toyomura et al, 2021).…”

Real-time magnetic resonance imaging reveals distinct vocal tract configurations during spontaneous and volitional laughter

“…Real-time MRI (rtMRI) data were fast gradient echo images collected on a Siemens 3T TIM Trio scanner; flip angle: 5°; TE/TR: 1.25/3.2 ms; GRAPPA factor 2; partial-Fourier: 75%; FOV 220 × 274 mm 2 ; 2.5 × 2.5 × 10.0 mm 3 spatial and 125 ms temporal resolution (8 frames per second (f.p.s.)). Although the frame rate is relatively slow compared with those reported in other vocal tract MRI studies [18,19,21], it was sufficient to capture the vocal portions of the behaviours measured in the current experiment. Each rtMRI run spanned 500 frames, to a total of 1500–2500 frames per participant per condition.…”

“…With its good spatial resolution of anatomical structures, it is possible to obtain global measures of the whole vocal tract in action while maintaining the ability to additionally analyse and interpret local effects (e.g. [16][17][18][19][20][21]).…”

Individual differences in vocal size exaggeration

“…Magnetic resonance imaging provides a non-invasive means of measuring the shape and size of the vocal tract 25 . This technology can be used to quantify differences between the vocal tracts of speakers 23 , 26 – 28 and dynamic changes to the shape of the vocal tract within speakers 29 , 30 . Singers for instance, have particular expertise in using vocal tract modulation in service of switching between modal and falsetto vocal registers 31 , 32 .…”