Modulation of the voice is a result of physiologic oscillation within one or more components of the vocal system including the breathing apparatus (i.e., pressure supply), the larynx (i.e. sound source), and the vocal tract (i.e., sound filter). These oscillations may be caused by pathologic tremor associated with neurological disorders like essential tremor or by volitional production of vibrato in singers. Because the acoustic characteristics of voice modulation specific to each component of the vocal system and the effect of these characteristics on perception are not well-understood, it is difficult to assess individuals with tremor affecting the voice and to determine the most effective interventions for reducing the perceptual severity of the disorder. The purpose of this study is to determine how the acoustic characteristics associated with laryngeal-based vocal tremor affect the perception of the magnitude of voice modulation, and to determine if adjustments can be made to the voice source and vocal tract filter to alter the acoustic output and reduce the perception of modulation. This research will be carried out using both a computational model of speech production and trained singers producing vibrato to simulate laryngeal-based vocal tremor. A kinematic model of the vocal folds coupled to a parametric model of the vocal tract area function will be used to simulate laryngeal-based vocal tremor with different voice source characteristics (i.e., vocal fold length and degree of vocal fold adduction) and different vocal tract filter characteristics (i.e., vowel shapes). It is expected that, by making adjustments to the voice source and vocal tract filter that reduce the amplitude of the upper harmonics, the characteristics of the acoustic output will be altered and the perception of magnitude of voice modulation will be reduced. In addition, trained singers will be asked to make the same adjustments to the voice source and vocal tract filter to investigate whether individuals can volitionally modify these characteristics to alter th acoustic output and reduce the perception of the magnitude of voice modulation. The findings from this study will have implications for selecting appropriate compensatory strategies to reduce the perceptual severity of modulation of the voice for individuals with tremor affecting the larynx.
The findings from this study will clarify how the acoustic characteristics associated with laryngeal-based vocal tremor and vibrato contribute to the perception of magnitude of modulation of the voice, as well as identify what physiologic modifications individuals can make to alter the acoustic output and reduce the perception of modulation. It is expected that this information will be useful in selecting appropriate compensatory strategies for individuals with tremor affecting the larynx to minimize the impact of this voice disorder on the lives of those affected by neurological disorders including essential tremor, cerebellar dysfunction, and dystonia.
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| Lester, Rosemary A; Story, Brad H (2015) The effects of physiological adjustments on the perceptual and acoustical characteristics of simulated laryngeal vocal tremor. J Acoust Soc Am 138:953-63 |
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