Asymmetries of the vocal folds and vocal fold vibration are key features underlying unilateral vocal fold motion impairment (VFMI). The knowledge of what particular asymmetries contribute to breathy voice and which asymmetries must be eliminated to re-establish normal voice will be important to improving evaluation and treatment of VFMI. It was hypothesized that several structural and vibratory asymmetries should lead to predictable changes in the glottal area, flow, and acoustic waveforms, and subsequently a perceived breathy voice quality. The purpose of this project was threefold: 1) to determine how specific vocal fold structural and vibratory asymmetries alter vocal function and perceived voice quality, 2) to determine the improvement in vocal function and voice quality in an abnormal voice with elimination of individual asymmetries, and 3) to develop a battery of vocal function measures that vary with dysphonia in a predictable manner. The approach was to use a computational kinematic model of vocal fold vibration that allows for differential left/right control of parameters such as vocal fold adduction, medial surface bulging, vibratory nodal point, phase, amplitude of vibration, and fundamental frequency. The resultant signals were subjected to aerodynamic and acoustic measurement as well as perceptual rating of voice quality. Results revealed that the degree of vocal process separation was the most influential parameter tested, though asymmetry of bulging, nodal point ratio, and starting phase worsened normal voice quality. Conversely, increased symmetry of bulging, nodal point ratio, amplitude of vibration and starting phase improved disordered voice quality. The amount of improvement to disordered voices varied based on the number of other asymmetries present. None of the six vocal function measures tested were primarily responsive to one particular model parameter, though four measures generally decreased as vocal process separation increased: maximum flow declination rate (MFDR), spectral slope (B0-B2), cepstral peak prominence (CPP), and harmonics-to-noise ratio (HNR). Two of the measures, MFDR and CPP, co-varied with each of the five parameters and robustly correlated with perceived severity.

This study attempted to replicate and expand previously published research in order to increase our understanding of how Vocal Function Exercises (VFE) might improve vocal function in normal voices. Measures were made to reflect potential post-treatment changes in acoustic and aerodynamic variables, including a measure of vocal efficiency. The participants of the study included 35 adults with normal voices. Each completed a series of speech tasks (sustained vowels, maximum phonation time, reading of a standardized passage, and repetition of syllable strings) before and after a four-week treatment period. Testing of pre- and post-treatment data revealed no clear improvement in acoustic and aerodynamic measures of the voice. There were also no significant improvements in vocal efficiency following the VFE. These findings suggest the need for further research to better understand the value of VFE in improving vocal function.

Understanding the involvement of the central nervous system (CNS) in voice production is essential to incorporating principles of neuroplasticity into therapeutic practice for voice disorders. Early steps to attaining this goal require the identification of specific neural biomarkers of the changes occurring in the CNS from a voice disorder and its subsequent treatment. In the absence of an adequate animal vocalization model, the larynx has not been acutely and reversibly perturbed to concurrently examine the effect on both peripheral and central processing of the altered input/output. Using a unique, reversible perturbation approach, it was the purpose of this study to perturb the larynx to mimic a voice disorder and study short-term neuroplastic response. Functional magnetic resonance imaging (fMRI) was the neuroimaging tool of choice for this study due to its superior spatial and temporal resolution. The voice was perturbed by anesthetizing the right recurrent laryngeal nerve, with a solution of lidocaine hydrochloride and epinephrine to induce a temporary right vocal fold paralysis. The paralysis lasted for approximately 90 minutes and had an overt presentation similar to that of a true vocal fold paralysis. Behavioral and fMRI data were obtained at three time points- baseline, during the vocal fold paralysis and one hour after recovery. Patterns of activity on fMRI during the three time points were found to be distinct on both subjective examination and statistical analysis. The regions of interest examined had distinct trends in activity as a function of the paralysis. Interestingly, males and females responded differently to the paralysis and its subsequent recovery. Strong correlation was not observed between the behavioral measures and fMRI activity reflecting a disparity between the overt presentation and recovery of vocal fold paralysis and cortical activity as seen on fMRI. The fictive paralysis model employed in this study provided a perturbation model for phonation that allowed us to examine behavioral and central neural correlates for disordered phonation in a controlled environment. Although this data is representative of acute changes from a transient paralysis, it provides an insight into the response of the cortex to sudden perturbation at the peripheral phonatory mechanism.

A significant part of an actor’s craft is creating and presenting characters with substantial credibility in order to stimulate a belief in the character from the point of view of an audience member (McGaw 1975; McGaw et al. 2011). To do this the actor relies on and utilizes his body, voice, imagination, experiences and so forth, for the creation of such characters (Zarrilli 1995; Benedetti 1998:5; Zarrilli 2002). This makes body and voice training within any actor training program pivotal. As an entry-level voice teacher in the tertiary situation I was confronted with a complex profile of the group of students to be taught. This profile influences or even determines the outcomes of the teaching opportunity. Gender differences were one of the most eminent markers of this complexity. For this project I decided to research the male voice as it possibly requires specific approaches to assist with the attainment of vocal ability. This study is concerned with the unique precepts of the male student actor in order to gain greater understanding of both the male physiological and anatomical construct, as well as the socio-cultural concept of ‘maleness’ as it refers to voice. Voice, in a cultural and societal paradigm, is subject to and as such influenced or shaped by social identity (Karpf 2006: 121). The actor’s socio-cultural paradigm potentially limits the vocal function and expression of the male voice in performance. This study draws on prior research when documenting unique and substantial structural differences typical of the male voice. It asks the question: What are the attributes that feed into the male student actor’s voice that have to be taken into account by the theatre voice teacher when viewed through anatomical, physiological and socio-cultural lenses? In order to answer the investigative question chapter two of this study consults scholarly materials concerning the various anatomical and physiological attributes of voice production (that is, its functional aspects) with specific reference to the male voice. It is argued that this can be seen as a description of voice production as object. Chapter three concerns itself with the impact of various socio-cultural influences on the voice with specific reference to the male voice. In this sense, the potentially subjective and image-defining concerns of the male voice that might impinge on vocal explorations are considered. Chapter four provides example explorations that may be used in a theatre voice class to indicate how the knowledge gained in chapters two and three will influence the facilitation of these explorations. It argues that it is an in-depth knowledge of voice, where voice materialises simultaneously both as object and as subject, that prepares the entry-level voice teacher to facilitate the development of the male student actor’s voice in a holistic manner. This dissertation concludes that, within the theatre voice training class, it is imperative that the voice teacher acknowledges and respects the sex-gender conflation of the male student actor and encourages him to explore and build a ‘voice’ that is capable of optimal expression in lieu its functional capabilities. / Dissertation (MA)--University of Pretoria, 2014. / tm2015 / Drama / MA / Unrestricted

Hydration of the vocal folds is important for the production of normal voice. Dehydration makes voice production more difficult and increases vocal effort. Laryngeal desiccation has been shown to increase phonation threshold pressure (PTP) and self-perceived phonatory effort (PPE) in females. Nebulized saline may reverse or offset this effect. However, few data exist regarding the effects of laryngeal desiccation and nebulized treatments in males. Further, the dose-response relationship between laryngeal desiccation and nebulized hydration treatments is unknown. This study examined the effects of two doses of nebulized isotonic saline following a laryngeal desiccation challenge in healthy male speakers. In a double-blinded, within-subjects design, 10 male college students (age range 18-26 years) attended two data collection sessions involving a 30-minute desiccation challenge followed by 3 mL or 9 mL of nebulized isotonic saline. PTP for the 10th and 80th fundamental frequency (F0) percentiles and PPE were collected before and after the desiccation challenge and at 5, 35, and 65 minutes after the nebulized treatment. PPE increased significantly following the laryngeal desiccation challenge (p < .01). Following nebulization, PPE decreased toward baseline for both doses of isotonic saline (p < .01), but failed to reverse the desiccation effect completely. No statistically significant changes in PTP occurred following the laryngeal desiccation challenge or subsequent treatments. Compared with previous research involving females, these results suggest males may respond differently to laryngeal desiccation and nebulized hydration treatments.

Vocal fold hydration is important for healthy function of the vocal mechanism. Vocal fold surface fluid protects the mucosa and facilitates efficient vocal fold oscillation. Dry air exposure, mouth breathing, insufficient intake of liquids, and behavioral factors may contribute to laryngeal dehydration. Singers are believed to be particularly at risk for voice problems related to dehydration due to environmental and voice use factors. Laryngeal desiccation and nebulized hydration treatments have been shown to influence phonation threshold pressure (PTP) and self-perceived phonatory effort (PPE) in females. However, little research exists exploring the effects of hydration in males. Additionally, few studies have examined the dose-response relationship of hydration treatments. This investigation examined the effects of a laryngeal desiccation challenge and two different doses of nebulized isotonic saline on voice production in trained male singers. In a double-blind, within-subjects repeated measures crossover investigation, 10 male singers (ages 18 to 24) received a 30 minute laryngeal desiccation challenge followed by either 3 mL or 9 mL of nebulized isotonic saline on two consecutive weeks. PTP, PPE, and self-perceived mouth and throat dryness were sampled during the following observations: predesiccation, post-desiccation, and at 5, 35, and 65 minutes post-nebulization. No differences in PTP were observed after desiccation or nebulized treatment. PPE, however, rose significantly after desiccation and returned near baseline after treatment. No significant differences between dosages were observed.

Voice is an important tool for communication. Consequently, voice disorders tend to severely diminish quality of life. Voice research seeks to understand the physics that govern voice production to improve treatment of voice disorders. This thesis develops a method for creating complex synthetic laryngeal models and obtaining flow data within these complex models. The method uses Computed Tomography (CT) scan data to create silicone models of the larynx. Index of refraction matching allows flow field data to be collected within a synthetic complex larynx, which had previously been impossible. A short proof-of-concept of the method is set forth. Details on the development of a mechanically-driven synthetic model are presented. Particle image velocimetry was used to collect flow field data in a complex and a simplified supraglottal model to study the effect of complex geometry on the supraglottal jet. Axis switching and starting and closing vortices were observed. The thesis results are anticipated to aid in better understanding flow structures present during voice production.

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[pt] O objetivo desta dissertação é classificar sinais de vozes, usando redes neurais, obtidos por meio de um modelo mecânico-estocástico para produção da voz humana, esse modelo foi construído a partir de uma abordagem probabilística não-paramétrica para considerar incertezas do modelo. Primeiro, uma rede neural artificial foi construída para classificar sinais de vozes reais, normais e provenientes de sujeitos com patologias nas cordas vocais. Como entradas da rede neural foram usadas medidas acústicas extraídas dos sinais glotais, obtidos por filtragem inversa dos sinais de vozes reais. Essa rede neural foi usada, posteriormente, para classificar sinais de vozes sintetizadas geradas por um modelo estocástico da produção da voz humana, no caso particular da geração de vogais. O modelo estocástico da produção da voz humana foi construído tomando por base o modelo determinístico criado por Ishizaka e Flanagan. Incertezas do modelo foram consideradas através de uma abordagem probabilística não-paramétrica de modo que matrizes aleatórias foram associadas às matrizes de massa, rigidez e amortecimento do modelo. Funções densidade de probabilidade foram construídas para essas matrizes, usando o Princípio da Máxima Entropia. O método de Monte Carlo foi usado para gerar realizaçoes de sinais de vozes. Os sinais obtidos foram então classificados usando a rede neural construída previamente. Das realizações obtidas, alguns sinais de vozes foram classificados como normais, porém outros foram classificados como provenientes de sujeitos com patologias nas cordas vocais. Os sinais com características de patologia foram classificados em três grupos: nódulo, paralisia unilateral e outras patologias. / [en] The aim of this thesis is to classify voice signals, using neural networks, obtained through a mechanical stochastic model for voice production, this model was built from a nonparametric probabilistic approach to take into account modeling uncertainties. At first, an artificial neural network was constructed to classify real voice signals, normal and produced by subjects with pathologies on the vocal folds. As inputs for the neural network were used acoustic measures extracted from the glottal signals, obtained by inverse filtering of the real voice signals. This neural network was used, later, to classify synthesized voice signal generated by a stochastic model of the voice production, in the particular case of vowels generation. The stochastic model was constructed from the corresponding deterministic model created by Ishizaka and Flanagan, in 1972. Modeling uncertainties were taken into account through a nonparametric probabilistic approach such that random matrices were associated to mass, stiffness and damping model matrices. Probability density functions were constructed for these matrices using the Maximum Entropy Principle. The Monte Carlo Method was used to generate realizations of the voice signals. The voice signals obtained were then classified using the neural network previously constructed. From the realizations obtained, some voice signals were classified as normal, but others were classified as produced by subjects with pathologies on the vocal folds. The signal with pathologies characteristics were classified into three groups: nodulus, unilateral paralysis and other pathologies.