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by surgically modifying the relative positions between laryngeal cartilages. However, this often reduces the vocal range and the amount of pitch change is relatively small. In feminization voice surgery in which a large pitch increase is desired, surgery is often performed to not only adjust vocal fold length but also to reduce the vibrating length of the vocal folds by surgically merging the anterior portions of the two vocal folds or reduc- ing vocal fold mass. Because pitch is only one of many aspects of gender perception, voice therapy is necessary in these patients to adjust other aspects of voice use such as vowel quality, stress, inflection, choice of words and conversational style.
Surgical intervention is also effective in treating some neurological voice disorders. For example, spasmodic dys- phonia is a neurological voice disorder that results from involuntary spasms in laryngeal muscle activity, which interferes with normal vocal fold vibration and leads to intermittent voice breaks and strained or breathy voice quality. Current treatment aims to weaken the affected laryngeal muscles through botulinum toxin injection or surgically denervating the affected laryngeal nerves, both of which can significantly alleviate the symptoms.
Bridging the Gap Between Science and Clinical Practice
Current clinical voice care is often quite effective in at least partially improving voice production and quality. How- ever, the voice outcome is often variable and relies heavily on the clinician’s experience. Sometimes the voice still remains unsatisfactory after intervention, and the under- lying reasons are often unclear. In this sense, clinical voice care is more art than science. The translation of findings from basic science voice research can play an important role in further improving clinical management of voice disorders and reducing variability in voice outcomes. For example, although vocal fold medial surface shape in the vertical dimension has been shown to be important to voice production (Zhang, 2016), it is often not monitored or targeted in current clinical voice examination and inter- vention, which focus on vocal fold position and glottal closure from a superior, endoscopic view. Targeting the medial surface shape in addition to other intervention goals may improve voice outcomes in patients whose voice remains unsatisfactory after intervention.
Many voice therapy techniques currently used in the clinic were modified from vocal training methods. Although many of them are effective, the underlying scientific principles often remain unclear. For example, semi-occluded vocal tract exercises are widely used in
the clinic. Although some theoretical hypotheses have been put forward, they are not always consistent with the observed changes in the laryngeal and vocal tract configuration during such exercises (Vampola et al., 2011). Voice therapy and vocal training often empha- size vibratory sensations in certain parts of the airway. However, it remains unclear what laryngeal and vocal tract adjustments are elicited in patients by voice ther- apy and which of them are responsible for improvement in voice outcomes. A better understanding of the scien- tific rationale would allow clinicians to better monitor the progress of voice therapy or even adapt voice ther- apy toward patient-specific vocal behavior to further improve voice therapy outcomes.
Each individual voice is unique. Although some indi- viduals are prone to vocal fold injury, others can talk loudly for an extended duration without experiencing vocal fatigue or noticeable voice changes. Little is known about the physiological and behavioral factors respon- sible for individual differences in vocal capabilities and vocal health. A mathematical model of voice production allowing manipulation of the voice in a physiologically realistic way would provide insights into why and how each individual voice is different (Wu and Zhang, 2019), which may lead to interesting applications both inside and outside the clinic.
Acknowledgments
I thank Maude Desjardins, Bruce Gerratt, Katherine Ver- dolini Abbott, Lisa Bolden, and Arthur Popper for their constructive comments on an earlier draft of this paper. I also acknowledge support from the National Institute on Deafness and Other Communication Disorders (NIDCD), National Institutes of Health (NIH), Bethesda, MD.
References
Berry, D., Verdolini, K., Montequin, D. W., Hess, M. M., Chan, R. W., and Titze, I. R. (2001). A quantitative output-cost ratio in voice production. Journal of Speech, Language, and Hearing Research 44, 29-37.
Boone, D. R., McFarlane, S. C., Von Berg, S. L., and Zraick, R. I. (2010). The Voice and Voice Therapy, 8th ed. Allyn & Bacon, Boston, MA.
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