Although it has been well accepted that vocal fold vibration and the resulting voice quality critically depend on vocal fold stiffness and geometry, the neuromuscular mechanisms regulating vocal fold stiffness and geometry still remain unclear. There has been no systematic, quantitative investigation of how and to what extent activation of laryngeal muscles, especially the interaction of the cricothyroid (CT) and thyroarytenoid (TA) muscles, affects the stiffness of the different layers of the vocal folds, and more importantly, how different stiffness conditions within the layered vocal fold affect the resulting vibration, acoustics, and voice quality. Laryngeal muscle activation also leads to simultaneous changes in vocal fold geometry, the influence of which on phonation is unclear. A better understanding of how laryngeal muscle activation regulates vocal fold stiffness and geometry and the resulting acoustics and voice quality may be useful for clinicians in the design and selection of treatment, or as part of intraoperative monitoring and assessment of treatment progress. This deficiency of understanding is largely due to the lack of an appropriate neuromuscular larynx model for conducting such systematic and quantitative investigations. Moreover, although there have been many studies focusing on either voice production or voice quality, there has been very little research exploring the cause-effect relation between physiology and perception. In this research, we propose to investigate the muscular processes of voice control in a recently-developed ex-vivo perfused living human larynx model (Berke et al., 2012), using our newly designed experimental approach (Zhang et al., 2012) that allows parametric muscle stimulation and observation of its influence on phonation in a virtually living human larynx. Computational studies are also proposed to facilitate interpretation and conceptualization of the experimental data. The two main questions to be addressed in the studies described here are: 1) What are the stiffness and geometry conditions that are required for normal phonation and how are they achieved through laryngeal muscle activation? and 2) How do left-right asymmetry in laryngeal muscle activation (commonly observed in voice disorders) affect vocal fold vibration, acoustics, and voice quality?
The proposed research is designed to provide an improved quantitative understanding of how laryngeal muscle activation affects the stiffness and geometry of the different layers of the vocal folds, and how interactions among laryngeal muscles affect the resulting acoustics and voice quality. Such knowledge will provide the ranges of stiffness and geometric conditions that are required for normal phonation and possibly serve as a foundation for future work toward improved diagnosis and treatment of voice disorders.
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