Auditory-Motor Control of Voice in Individuals with Essential Vocal Tremor

Essential tremor (ET) is the most prevalent movement disorder affecting nearly one in every 100 people worldwide. Up to sixty-two percent of individuals with ET develop vocal tremor (VT), a hyperkinetic neurological speech disorder. VT is characterized by modulation of the frequency (pitch) and amplitude (loudness) of the voice, which results in a ‘shaky’ sounding voice and increased effort during speech production. Neurogenic speech disorders like VT are detrimental to communication, professional productivity, and quality of life. Unfortunately, the current approaches for medical management of VT have inconsistent effects on voice production and often cause adverse effects. Furthermore, there is limited evidence supporting the benefit of behavioral management for VT. The challenges in managing VT stem from a lack of understanding of the underlying sensorimotor deficits in this population. Previous research on typical sensorimotor control of voice demonstrated that healthy speakers use auditory feedback for immediate correction of pitch errors and prevention of future errors. Based on the Directions into the Velocities of Articulators (DIVA) model, a computational model accounting for normal and disordered speech motor control, a neural network of feedback and feedforward mechanisms drive auditory- motor responses and ensure that any mismatch between the intended voice output and actual voice output is corrected. When individuals with VT attempt to produce a steady pitch, their voice output is characterized by a 4-8 Hz involuntary modulation of the fundamental frequency and amplitude. It is unknown whether the feedback and/or feedforward systems attempt to correct for these modulations and stabilize the voice output, or if there is dysfunction of these systems that further contributes to the modulated output. Thus, this study aims to investigate how auditory feedback influences pitch control in individuals with VT compared with healthy speakers. The findings of this study may improve the understanding of sensorimotor control in VT and guide development of sensorimotor-based treatments for the disorder. Additionally, this will be a novel application of the current models of feedforward and feedback auditory-motor control, which may help refine these computational models and motivate future research.