Voice tremor: what we know and what we do not know

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Abstract
Voice tremor is a feature of many neurological conditions. Historically, clinical evaluation of voice tremor has relied on auditory-perceptual evaluation. We review developments in understanding of voice tremor that advocate additional approaches (acoustic, fibreoptic nasolaryngoscopic examination) to evaluation and stress the contribution from multiple sites in the speech mechanism to perceived tremor. An isolated focus on the speech signal does not identify the source/s of tremor. Structures in the pharynx and larynx can be important sources of perceived voice tremor. In addition to a sustained vowel phonatory task for evaluation, fibreoptic nasolaryngoscopic examination is recommended to observe tremor behaviour in different anatomic sites using different speech tasks; acoustic analysis is recommended to quantify tremor and enhance understanding of underlying mechanisms. Tremor measures (rate, periodicity, magnitude of frequency and amplitude tremor) have proved useful in differentiating speakers with tremor from normal speakers. Differentiating between tremor aetiologies is proving more challenging. The investigation of a conceptual model of voice tremor to understand the effect that oscillations in different parts of the speech mechanism have on the speech signal is an important development in the field. A sustained phonatory vowel task with fibreoptic nasolaryngoscopic examination of pharyngeal and laryngeal musculature, supplemented by acoustic measures, is currently recommended for clinical identification, quantification and characterization of voice tremor.