Vibrational energy created at the larynx during speech will deflect vestibular mechanoreceptors in humans (Todd et al., 2008; Curthoys, 2017; Curthoys et al., 2019). Vestibular-evoked myogenic potential (VEMP), an indirect measure of vestibular function, was assessed in 15 participants who stutter, with a non-stutter control group of 15 participants paired on age and sex. VEMP amplitude was 8.5 dB smaller in the stutter group than the non-stutter group (p = 0.035, 95% CI [−0.9, −16.1], t = −2.1, d = −0.8, conditional R2 = 0.88). The finding is subclinical as regards gravitoinertial function, and is interpreted with regard to speech-motor function in stuttering. There is overlap between brain areas receiving vestibular innervation, and brain areas identified as important in studies of persistent developmental stuttering. These include the auditory brainstem, cerebellar vermis, and the temporo-parietal junction. The finding supports the disruptive rhythm hypothesis (Howell et al., 1983; Howell, 2004) in which sensory inputs additional to own speech audition are fluency-enhancing when they coordinate with ongoing speech.
Speech-motor and psycholinguistic models employ feedback control from an auditory stream corresponding to own voice. Such models underspecify how own voice is identified. It is proposed that coincidence detection between cochlear and vestibular streams identifies own voice in mammals (H1) and that the coincidence detection differs in people who stutter (H2). Vestibular-evoked myogenic potential (VEMP), an indirect measure of vestibular function, was assessed in 15 people who stutter, with controls paired on age and sex. VEMP amplitude was 8.5 dB smaller in people who stutter than paired controls (p = 0.035, 95% CI [-0.9, -16.1], t = -2.1, d = -0.8, conditional R2 = 0.88), suggesting an approximate halving in how they perceptually experience the vestibular component of own voice. H1 and H2 are supported in this initial test of both hypotheses. Discussion covers own voice identification, persistent developmental stuttering, speech-induced suppression, auditory scene analysis, and theories of mental content.
The cervical vestibular-evoked myogenic potential (VEMP) was assessed in 24 women and 24 men having a mean age of 19.5 years (SD 0.7). Whilst there was no group difference in VEMP peak to trough (p1-n1) amplitude, VEMP p1-n1 latency was found to be shorter for women than for men by 2.4 ms (95% CI [-0.9, -3.9], chi squared (1) 9.6, p = 0.0020). This equates to 21% of the mean 11.4 ms VEMP p1-n1 latency across women and men. It is a reversal of findings in several prior studies, which are reviewed here. Statistical modelling based on the current study suggests some prior studies were underpowered to detect a sex difference in VEMP latency. Possible causes for sex difference in VEMPs are discussed. Candidate explanations include head resonance, superposition of motor unit action potentials and influence of sex hormones. These explanations are not mutually exclusive, and multiple factors may contribute to difference in VEMP measurement between women and men. This study used a methodology developed in Gattie et al. (2021), which addresses sound exposure concerns with the high amplitude air conducted stimuli necessary to evoke a VEMP response. It is suggested that body conducted stimuli may be preferable for VEMP testing in which ear-specific information is not required.
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