Index of content:
Volume 122, Issue 4, October 2007
- SPEECH PRODUCTION 
Asymmetric airflow and vibration induced by the Coanda effect in a symmetric model of the vocal folds122(2007); http://dx.doi.org/10.1121/1.2773960View Description Hide Description
A model constructed from Navier-Stokes equations and a two-mass vocal fold description is proposed in this study. The composite model not only has the capability to describe the aerodynamics in a vibratory glottis but also can be used to study the vocal fold vibration under the driving of the complex airflow in the glottis. Numerical simulations show that this model can predict self-oscillations of the coupled glottalaerodynamics and vocal fold system. The Coanda effect could occur in the vibratory glottis even though the vocal folds have left-right symmetric prephonatory shape and tissue properties. The Coanda effect causes the asymmetric flow in the glottis and the difference in the driving force on the left and right vocal folds. The different pressures applied to the left and right vocal folds induce their displacement asymmetry. By using various lungpressures to drive the composite model, it was found that the asymmetry of the vocal fold displacement is increased from 1.87% to 11.2%. These simulation results provide numerical evidence for the presence of asymmetric flow in the vibratory glottis; moreover, they indicate that glottalaerodynamics is an important factor in inducing the asymmetric vibration of the vocal folds.
Physical mechanisms of phonation onset: A linear stability analysis of an aeroelastic continuum model of phonation122(2007); http://dx.doi.org/10.1121/1.2773949View Description Hide Description
In an investigation of phonation onset, a linear stability analysis was performed on a two-dimensional, aeroelastic, continuum model of phonation. The model consisted of a vocal fold-shaped constriction situated in a rigid pipe coupled to a potential flow which separated at the superior edge of the vocal fold. The vocal fold constriction was modeled as a plane-strain linear elastic layer. The dominant eigenvalues and eigenmodes of the fluid-structure-interaction system were investigated as a function of glottal airflow. To investigate specific aerodynamic mechanisms of phonation onset, individual components of the glottal airflow (e.g., flow-induced stiffness, inertia, and damping) were systematically added to the driving force. The investigations suggested that flow-induced stiffness was the primary mechanism of phonation onset, involving the synchroniza-tion of two structural eigenmodes. Only under conditions of negligible structural damping and a restricted set of vocal fold geometries did flow-induced damping become the primary mechanism of phonation onset. However, for moderate to high structural damping and a more generalized set of vocal fold geometries, flow-induced stiffness remained the primary mechanism of phonation onset.
122(2007); http://dx.doi.org/10.1121/1.2772230View Description Hide Description
The purpose of this study was to find relationships between subglottal pressure and fundamental frequency of phonation in excised larynx models. This included also the relation between and its rate of change with pressure. Canine larynges were prepared and mounted over a tapered tube that supplied pressurized, heated, and humidified air. Glottal adduction was accomplished either by using two-pronged probes to press the arytenoids together or by passing a suture to simulate lateral cricoarytenoid muscle activation. The pressure-frequency relation was obtained through a series of pressure-flow sweep experiments that were conducted for eight excised canine larynges. It was found that, at set adduction and elongation levels, the pressure-frequency relation is nonlinear, and is highly influenced by the adduction and elongation. The results indicated that for the lower phonation mode, the average rate of change of frequency with pressure was , and for the higher mode was for adduction changes and for elongation changes. The results suggest that during speech and singing, the relationships are taken into account.
122(2007); http://dx.doi.org/10.1121/1.2773966View Description Hide Description
The role of auditory feedback in speech motor control was explored in three related experiments.Experiment 1 investigated auditory sensorimotor adaptation: the process by which speakers alter their speech production to compensate for perturbations of auditory feedback. When the first formant frequency (F1) was shifted in the feedback heard by subjects as they produced vowels in consonant-vowel-consonant (CVC) words, the subjects’ vowels demonstrated compensatory formant shifts that were maintained when auditory feedback was subsequently masked by noise—evidence of adaptation. Experiment 2 investigated auditory discrimination of synthetic vowel stimuli differing in F1 frequency, using the same subjects. Those with more acute F1 discrimination had compensated more to F1 perturbation. Experiment 3 consisted of simulations with the directions into velocities of articulators model of speech motor planning, which showed that the model can account for key aspects of compensation. In the model, movement goals for vowels are regions in auditory space; perturbation of auditory feedback invokes auditory feedback control mechanisms that correct for the perturbation, which in turn causes updating of feedforward commands to incorporate these corrections. The relation between speaker acuity and amount of compensation to auditory perturbation is mediated by the size of speakers’ auditory goal regions, with more acute speakers having smaller goal regions.