Breathy Voice as a Compensatory Strategy for Essential Vocal Tremor: A Single Case Experiment Across Participants

Abstract

Essential vocal tremor (EVT) manifests as nearly rhythmic modulations of fundamental frequency (fo) and intensity and causes a shaky voice. Although research on behavioral therapy for EVT is limited, previous studies have shown that a breathy voice reduces the perception of simulated EVT and might be an effective compensatory strategy. The current study aimed to measure the acoustical and perceptual effects of a breathy voice strategy in speakers with EVT. A single-case experimental design (SCED) was used to investigate acoustical effects, and a pair comparison listening task was used to investigate perceptual effects. Three participants with EVT matched five different levels of breathiness produced by a computational model. Acoustical analyses of the rate and extent of fo and intensity modulation were performed to estimate EVT severity for baseline and treatment trials. Statistical analyses were completed using Tau-U. Twenty novice listeners participated in the perceptual study to determine if treatment trials sounded less "shaky" than baseline trials. Statistical analyses were completed using one sample ttests. The acoustical effects were variable across different levels of breathiness for all three participants. All participants were able to adjust their levels of breathiness based on auditory models and verbal cues but did not achieve the target levels of breathiness. Listeners did not perceive the breathy trials to be less "shaky" than baseline trials for any level of breathiness. The breathy voice strategy had variable effects on the acoustical measures of EVT, supporting the use of a single-case experimental design to investigate the effectiveness of behavioral treatment for EVT. Listeners perceived breathy trials to be "shakier" than baseline trials, which was inconsistent with our hypothesis and previous studies of EVT. Future research should evaluate the use of a breathy voice in speakers with confirmed laryngeal tremor, optimize cueing for breathiness, and provide more opportunities to practice the breathy strategy.