Frequency Of Phonation Research Articles

Design and characterization of a dynamic vibrational culture system

To engineer a functional vocal fold tissue, the mechanical environment of the native tissue needs to be emulated in vitro. We have created a dynamic culture system capable of generating vibratory stimulations at human phonation frequencies. The novel device is composed of a function generator, a power amplifier, an enclosed loudspeaker and a circumferentially-anchored silicone membrane. The vibration signals are translated to the membrane aerodynamically by the oscillating air pressure underneath. The vibration profiles detected on the membrane were symmetrical relative to the centre of the membrane as well as the resting position over the range of frequencies (60-300 Hz) and amplitudes tested (1-30 µm). The oscillatory motion of the membrane gave rise to two orthogonal, in-plane strain components that are similar in magnitude (0.47%) and are strong functions of membrane thickness. Neonatal foreskin fibroblasts (NFFs) attached to the membrane were subjected to a 1 h vibration at 60, 110 and 300 Hz, with the displacement at the centre of the membrane varying in the range 1-30 µm, followed by a 6 h rest. These regimens did not cause morphological changes to the cells. An increase in cell proliferation was detected when NFFs were driven into oscillation at 110 Hz with a normal displacement of 30 µm. qPCR results showed that the expression of genes encoding some extracellular matrix proteins was altered in response to changes in vibratory frequency and amplitude. The dynamic culture device provides a potentially useful in vitro platform for evaluating cellular responses to vibration.

Injection of human mesenchymal stem cells improves healing of vocal folds after scar excision—A xenograft analysis

Using a xenograft model the aim was to analyze if injection of human mesenchymal stem cells (hMSC) into the rabbit vocal fold (VF), after excision of an established scar, can improve the functional healing of the VF. Prospective design with an experimental xenograft model. The VFs of 12 New Zealand rabbits were injured by a bilateral localized resection. After 9 weeks the scar after the resection was excised and hMSC were injected into the VFs. After another 10 weeks 10 VFs were dissected and stained for histology. Lamina propria thickness and relative content of collagen type I were measured. Viscoelasticity of 14 VFs at phonatory frequencies was quantified by a simple-shear rheometer. The hMSC survival was determined using a human DNA specific reference probe, that is, FISH analysis. The viscoelastic measurements, that is, dynamic viscosity and elastic shear modulus for the hMSC-treated VFs, were found to be similar to those of normal controls and were significantly lower than those of untreated controls (P < .05). A significant reduction in lamina propria thickness was also shown for the hMSC treated VFs compared with the untreated VFs (P < .05). This histologic finding corresponded with the viscoelastic results. No hMSC survived 10 weeks after the injection. Human mesenchymal stem cells injected into the rabbit VF following the excision of a chronic scar, were found to enhance the functional healing of the VF with reduced lamina propria thickness and restored viscoelastic shear properties.

Mathematical Models and Numerical Schemes for the Simulation of Human Phonation

Acoustic data has long been harvested in fundamental voice investigations since it is easily obtained using a microphone. However, acoustic signals alone do not reveal much about the complex interplay between sound waves, structural surface waves, mechanical vibrations, and fluid flow involved in phonation. Available high speed imaging techniques have over the past ten years provided a wealth of information about the mechanical deformation of the superior surface of the larynx during phonation. Time-resolved images of the inner structure of the deformable soft tissues are not yet feasible because of low temporal resolution (MRI and ultrasound) and x-ray dose-related hazards (CT and standard x- ray). One possible approach to circumvent these challenges is to use mathematical models that reproduce observable behavior such as phonation frequency, closed quotient, onset pressure, jitter, shimmer, radiated sound pressure, and airflow. Mathematical models of phonation range in complexity from systems with relatively small degrees of freedom (multi-mass models) to models based on partial differential equations (PDEs) mostly solved by finite element (FE) methods resulting in millions of degrees-of-freedom. We will provide an overview about the current state of mathematical models for the human phonation process, since they have served as valuable tools for providing insight into the basic mechanisms of phonation and may eventually be of sufficient detail and accuracy to allow surgical planning, diagnostics, and rehabilitation evaluations on an individual basis. Furthermore, we will also critically discuss these models w.r.t. the used geometry, boundary conditions, material properties, their verification, and reproducibility.

Ventricular Fold Phonation: Viscoelastic Properties and HSDI

Objective: Determine the functional biomechanical properties of the human false vocal fold mucosa at phonatory frequencies, in comparison with those of the true vocal fold cover; and to quantify the vibration patterns of ventricular fold phonation with HSDI (high speed digital imaging). Method: Viscoelastic shear properties of false fold specimens were quantified as functions of frequency, with measurements of elastic shear modulus (G′) and dynamic viscosity (h′) at up to 250 Hz using a simple-shear rheometer. Ventricular fold phonation of three subjects was analyzed by HSDI (high speed digital imaging) through kymography and laryngotopography. Results: All specimens showed similar frequency dependence of their viscoelastic properties, with G′ gradually increasing with frequency and h′ monotonically decreasing with frequency. G′ and h′ of the false fold mucosa were generally higher than those of the true vocal fold cover, although the differences did not reach statistical significance. Kymographic and laryngotopographic analysis of high speed digital images revealed vibration of the false fold mucosa for subjects undergoing ventricular fold phonation. The vibratory frequencies were lower than typical fundamental frequencies for phonation. Conclusion: These findings showed false folds could function as a secondary sound source. These preliminary data suggested that the false fold mucosa could serve as replacement material for patients with unrepairable vocal fold cover damage.

Effects of Compliance Monitoring of Vocal Function Exercises on Voice Outcome Measures for Normal Voice

This experimental study examined the efficacy of the vocal function exercise program in improving voice production in individuals with normal voices. 20 young women (M age = 22 yr.) with normal voices, 10 in the Monitored compliance group and 10 in the Unmonitored compliance group, received training in performing vocal function exercises followed by daily practice of the exercises for 28 consecutive days. Participants in the Monitored compliance group were required to submit audio or video recordings of their daily practice of vocal function exercises, and those in the Unmonitored compliance group were not required to record their daily practice sessions. Results indicated that while the participants in both groups significantly increased maximum phonation times and maximum phonational frequency ranges, those in the Monitored group improved significantly more than the participants in the Unmonitored group on these outcome measures.

Optical measurements of vocal fold tensile properties: Implications for phonatory mechanics

In voice research, in vitro tensile stretch experiments of vocal fold tissues are commonly employed to determine the tissue biomechanical properties. In the standard stretch-release protocol, tissue deformation is computed from displacements applied to sutures inserted through the thyroid and arytenoid cartilages, with the cartilages assumed to be rigid. Here, a non-contact optical method was employed to determine the actual tissue deformation of vocal fold lamina propria specimens from three excised human larynges in uniaxial tensile tests. Specimen deformation was found to consist not only of deformation of the tissue itself, but also deformation of the cartilages, as well as suture alignment and tightening. Stress–stretch curves of a representative load cycle were characterized by an incompressible Ogden model. The initial longitudinal elastic modulus was found to be considerably higher if determined based on optical displacement measurements than typical values reported in the literature. The present findings could change the understanding of the mechanics underlying vocal fold vibration. Given the high longitudinal elastic modulus the lamina propria appeared to demonstrate a substantial level of anisotropy. Consequently, transverse shear could play a significant role in vocal fold vibration, and fundamental frequencies of phonation should be predicted by beam theories accounting for such effects.

Vocal Fold Mass Is Not A Useful Quantity for Describing F 0 in Vocalization

Confusion exists about the effect of mass and size of the vocal folds on fundamental frequency (F0) of phonation. In particular, greater vocal fold thickness is often assumed to be associated with lower F0. The purpose here is to show that such a relationship does not exist and that F0 should be conceptualized with quantities other than mass (i.e., length and tissue stress). Arguments are made on the basis of fundamental laws of mechanics (point-mass vs. distributed mass). In speech science, phonetics, and animal vocalization disciplines, instruction should shift away from point-mass descriptions of vocal fold tissue and toward an understanding of mode frequencies in an elastic continuum.

A test of formant frequency analyzes with simulated child-like vowels.

Speech production by children is typically characterized by a fairly high fundamental frequency of phonation and a short vocal tract length that produces high formant frequencies. Together these two characteristics contribute to the difficulty of making accurate measurements of the formants because the vocal tract transfer function may be undersampled by the voice source harmonics. In addition, the close proximity of the low-numbered harmonics (including the fundamental) to a formant may lead to strong nonlinear interaction of the acoustic pressures in the vocal tract and the glottal airflow. The purpose of this study was to use standard spectrographic and LPC techniques, as well as new pitch-synchronous method, to measure formant frequencies of child-like vowels that have been simulated with a speech production model. Each vowel will be simulated with two different representations of the voice source: a glottal area model that allows for nonlinear source-tract interaction and a glottal flow model in which vocal tract characteristics cannot affect the source. The results of the analyzes will be compared to the actual formant frequencies calculated directly from the known vocal tract area functions used to generate the vowels. [Research supported by NIH R01-DC04789.]

Voice Training and Changing Weight—Are They Reflected in Speaking Fundamental Frequency, Voice Range, and Pitch Breaks of 13-Year-Old Girls? A Longitudinal Study

Assessment of the voice-change progress of 20 girls (12-13 years) over 1 year by observing changes in speaking fundamental frequency (SFo), voice range, and register pitch breaks in the context of weight, height, voice training, and self-perception. One-year longitudinal collective case study. Twenty girls were recorded at the beginning and end of a year; nine girls were recorded another three times. SFo, vocal range, and characteristics were analyzed and interactions between these data assessed against weight and height to indicate pubertal development, and to test the hypothesis that changes in weight, height, SFo, and pitch breaks were related. Effects of training and the girls' self-perception of their voice use were also assessed. Vocal characteristics changed as the girls passed through different weight ranges. During 47.5-52.4 kg (called band 2) and 52.4-57.5 kg (band 3), there was progressive contraction of vocal range and in some girls a slight rise in SFo between recording times 1 and 5. Both high- and low-pitch breaks were present in 45% of girls' voices. Girls in band 4 (<57.5 kg) had an increased vocal range, and pitch breaks in vocal-range areas that indicated the development of adult vocal registers. In this study, voice-trained girls were heavier, had higher SFo, used wider speech-range inflection, had a higher vocal range, and greater voice-use confidence; all girls lost confidence in their voice use over the year. In this longitudinal study of twenty 13-year-old girls, voice changes in SFo, vocal range, and pitch-break frequency were synchronous with certain weight ranges. Girls with training registered higher maximum phonational frequency and were more confident in their voice use than girls without training.

Rheometric properties of canine vocal fold tissues: Variation with anatomic location

Objective To evaluate the in vitro rheometric properties of the canine vocal fold lamina propria and muscle at phonatory frequencies, and their changes with anatomic location. Methods Six canine larynges were harvested immediately postmortem. Viscoelastic shear properties of anterior, middle, and posterior portions of the vocal fold cover (lamina propria) as well as those of the medial thyroarytenoid (TA) muscle (vocalis muscle) were quantified by a linear, controlled-strain simple-shear rheometer. Measurements of elastic shear modulus ( G′) and dynamic viscosity ( η′) of the specimens were conducted with small-amplitude sinusoidal shear deformation over a frequency range of 1–250 Hz. Results All specimens showed similar frequency dependence of the viscoelastic functions, with G′ gradually increasing with frequency and η′ decreasing with frequency monotonically. G′ and η′ of the canine vocalis muscle were significantly higher than those of the canine vocal fold cover, and η′ of the canine vocal fold cover was significantly higher than that of the human vocal fold cover. There were no significant differences in G′ and in η′ between different portions of the canine vocal fold cover. Conclusion These preliminary data based on the canine model suggested that the vocalis muscle, while in a relaxed state in vitro, is significantly stiffer and more viscous than the vocal fold cover during vibration at phonatory frequencies. For large-amplitude vocal fold vibration involving the medial portion of the TA muscle, such distinct differences in viscoelastic properties of different layers of the vocal fold should be taken into account in multi-layered biomechanical models of phonation.

Vibration in a self-oscillating vocal fold model with left-right asymmetry in body-layer stiffness

This study compares the phonatory behavior of an asymmetric vocal fold model to that of each individual vocal fold model in a hemi-configuration. Although phonation frequencies of the two folds in hemi-configurations had a ratio close to 1:3, a subharmonic synchronization between the two folds was not observed in the asymmetric model. Instead, the vibratory behavior was dominated by the dynamics of one fold only, and the other fold was enslaved to vibrate at the same frequency. Increasing subglottal pressure induced a shift in relative dominance between the two folds, leading to abrupt changes in both vibratory pattern and frequency.

The Effect of Smoking on the Dysphonia Severity Index in Females

Objective: This study investigated the capability of the Dysphonia Severity Index (DSI) and its component measures to reveal differences in vocal capability between groups of young adult female smokers and nonsmokers. Patients and Methods: The subjects were 30 female nonsmokers and 30 female smokers between the ages of 18 and 24 years. Data on the DSI components (maximum phonation time, MPT; highest phonational frequency, F_{0 high}; lowest intensity, I_low, and jitter) were collected, followed by calculation of the DSI. Results: Significant differences between groups were observed on the DSI, with reduced DSI scores in smokers primarily due to reductions in F_{0 high} and increases in I_low. A strong partial correlation between MPT and the DSI in smokers may be indicative of reductions in respiratory support and/or phonatory control. Conclusions: Significant group differences in the DSI and component measures may be indicative of early changes in vocal function secondary to smoking. Reductions in frequency and dynamic range are consistent with the possibility of increased vocal fold mass in smokers. The results indicate that significant differences in the DSI between groups may be observed in subjects with perceptually normal vocal quality and with normal levels of vocal perturbation.

Some Phonatory and Resonatory Characteristics of the Rock, Pop, Soul, and Swedish Dance Band Styles of Singing

This investigation aims at describing voice function of four nonclassical styles of singing, Rock, Pop, Soul, and Swedish Dance Band. A male singer, professionally experienced in performing in these genres, sang representative tunes, both with their original lyrics and on the syllable /pae/. In addition, he sang tones in a triad pattern ranging from the pitch Bb2 to the pitch C4 on the syllable /pae/ in pressed and neutral phonation. An expert panel was successful in classifying the samples, thus suggesting that the samples were representative of the various styles. Subglottal pressure was estimated from oral pressure during the occlusion for the consonant [p]. Flow glottograms were obtained from inverse filtering. The four lowest formant frequencies differed between the styles. The mean of the subglottal pressure and the mean of the normalized amplitude quotient (NAQ), that is, the ratio between the flow pulse amplitude and the product of period and maximum flow declination rate, were plotted against the mean of fundamental frequency. In these graphs, Rock and Swedish Dance Band assumed opposite extreme positions with respect to subglottal pressure and mean phonation frequency, whereas the mean NAQ values differed less between the styles.

A computational study of the effect of vocal-fold asymmetry on phonation

Unilateral laryngeal paralysis leads to tension imbalance and hence to asynchronous movements between the two vocal folds during phonation. In the current study, a computational model of phonation that couples a two-mass model of the vocal folds with a Navier-Stokes model of the glottal airflow, has been used to examine the dynamics of vocal fold configurations with tension imbalance and its implications for phonation. The simulations show that tension imbalance influences phonation onset, intensity as well as the fundamental phonation frequency. Distinct non-linear effects such as period-doubling bifurcation and preferential frequency selection are also observed.

Dependence of phonation threshold pressure and frequency on vocal fold geometry and biomechanics

Previous studies show that phonation onset occurs as two eigenmodes of the vocal folds are synchronized by the interaction between the vocal folds and the glottal flow. This study examines the influence of the geometrical and biomechanical properties of the vocal folds on this eigenmode-synchronization process, with a focus on phonation threshold pressure and frequency. The analysis showed that phonation threshold pressure was determined by the frequency spacing and coupling strength between the two natural modes that were synchronized by the fluid-structure interaction. The phonation frequency at onset was the root mean square value of the two natural frequencies plus a correction due to the added stiffness of the glottal flow. When higher-order modes of the vocal fold structure were included, more than one group of eigenmodes was synchronized as the system moved toward phonation onset. Changes in vocal fold biomechanics may change the relative dominance between different groups and cause phonation onset to occur at a different eigenmode, which was often accompanied by an abrupt change in onset frequency. Due to the synchronization of multiple pairs of eigenmodes and the mode-switching possibility, a complete and accurate description of vocal fold biomechanical properties is needed to determine the final synchronization pattern and obtain a reliable calculation of the dependence of phonation threshold pressure and frequency on vocal fold geometry and other biomechanical properties.

Viscoelastic properties of phonosurgical biomaterials at phonatory frequencies

The purpose of this study was to examine the functional biomechanical properties of several injectable biomaterials currently or potentially used for vocal fold augmentation. Rheometric investigation of phonosurgical materials in vitro. Linear viscoelastic shear properties of 3% bovine collagen (atelocollagen), micronized AlloDerm (Cymetra; LifeCell Corp., Branchburg, NJ), calcium hydroxylapatite (CaHA) (Radiesse; BioForm Medical, San Mateo, CA), and 2.4% cross-linked hyaluronic acid (HA) gel (Juvéderm; Allergan, Inc., Irvine, CA) were quantified as functions of frequency covering the phonatory range, and compared to those of the human vocal fold cover. Measurements of elastic shear modulus (G') and dynamic viscosity (eta') were made at up to 250 Hz with a controlled-strain simple-shear rheometer. Linear least-squares regression was conducted to curve-fit log G' and log eta' versus log frequency, and statistical analysis was performed with one-way analysis of variance. Radiesse and Cymetra were found to be the stiffest and the most viscous materials, followed by Juvéderm and atelocollagen. There were significant differences in the magnitudes of G' and eta' among the phonosurgical materials and the normal human vocal fold cover (p < .001), whereas there was no significant difference in the frequency dependence of G' and eta' among the materials. Post hoc Tukey tests revealed significant differences (p < .05) in pairwise comparisons of the magnitudes of G' and eta' among all materials and the vocal fold cover. These findings suggested that although these biomaterials may be injected lateral to the lamina propria for the treatment of glottic insufficiency, none of them are rheologically optimal for the functional reconstruction of the vocal fold lamina propria.

Classification of functional voice disorders based on phonovibrograms

This work presents a computer-aided method for automatically and objectively classifying individuals with healthy and dysfunctional vocal fold vibration patterns as depicted in clinical high-speed (HS) videos of the larynx. By employing a specialized image segmentation and vocal fold movement visualization technique - namely phonovibrography - a novel set of numerical features is derived from laryngeal HS videos capturing the dynamic behavior and the symmetry of oscillating vocal folds. In order to assess the discriminatory power of the features, a support vector machine is applied to the preprocessed data with regard to clinically relevant diagnostic tasks. Finally, the classification performance of the learned nonlinear models is evaluated to allow for conclusions to be drawn about suitability of features and data resulting from different examination paradigms. As a reference, a second feature set is determined which corresponds to more traditional voice analysis approaches. For the first time an automatic classification of healthy and pathological voices could be obtained by analyzing the vibratory patterns of vocal folds using phonovibrograms (PVGs). An average classification accuracy of approximately 81% was achieved for 2-class discrimination with PVG features. This exceeds the results obtained through traditional voice analysis features. Furthermore, a relevant influence of phonation frequency on classification accuracy was substantiated by the clinical HS data. The PVG feature extraction and classification approach can be assessed as being promising with regard to the diagnosis of functional voice disorders. The obtained results indicate that an objective analysis of dysfunctional vocal fold vibration can be achieved with considerably high accuracy. Moreover, the PVG classification method holds a lot of potential when it comes to the clinical assessment of voice pathologies in general, as the diagnostic support can be provided to the voice clinician in a timely and reliable manner. Due to the observed interdependency between phonation frequency and classification accuracy, in future comparative studies of HS recordings of oscillating vocal folds homogeneous frequencies should be taken into account during examination.

Vocal Fold Elasticity in the Pig, Sheep, and Cow Larynges

Elastic characteristics of the pig, sheep, and cow vocal folds were investigated through a series of in vitro experiments. Sample strips of the vocal-fold tissue were dissected from pig, sheep, and cow vocal folds and mounted inside a saline-filled ergometer chamber that was maintained at 37°C ± 1°C. Sinusoidal elongation was applied on the samples to obtain the passive force measurements. Force and elongation data from the samples were recorded electronically with a dual-servo system (ergometer). Stress-Strain data were compared to characterize the interspecies differences in the elastic properties of vocal folds. Pig vocal folds exhibited the most nonlinear stress-strain relationship, indicating the presence of a high level of collagen fibers. Cow vocal folds had the highest Young's modulus, but the tissue displayed a nearly linear stress-strain profile. Previous studies of phonation in these three species have indicated that pig larynges have the highest range of phonation frequencies, making them a good candidate for animal studies. The current study provides quantitative data for the elastic properties of the oscillating laryngeal tissue in these species and indicates that nonlinear behavior of these tissues may lead to wider oscillation ranges.

A Comparison of Trained and Untrained Vocalists on the Dysphonia Severity Index

The purposes of this study were (1) to compare trained and untrained singers on the Dysphonia Severity Index (DSI) and its component measures, and (2) to contribute to normative DSI data for trained singers. This study included 36 untrained participants (15 males and 21 females) and 30 participants (15 males and 15 females) with singing experience between the ages of 18 and 30 years. Measures of maximum phonation time (MPT), highest phonational frequency, lowest intensity, and jitter were obtained for each subject and incorporated into the previously published multivariate DSI formula. Results indicated that vocally trained subjects have significantly higher DSI scores than untrained subjects (mean DSI: 6.48 vs 4.00, respectively), with significant differences observed between trained and untrained groups for three of the four components of the DSI (F(0) high; I low; jitter). The findings of this study are consistent with previous reports that indicate significant increases in the DSI with vocal training, and with various studies that have observed increased vocal capability in trained singers versus their untrained counterparts. The results of this study indicate that alternative normative expectations for the DSI may need to be taken into account when using the DSI with patients who have participated in directed vocal training, such as choral participation and voice/singing lessons.

Vocal Attractiveness Increases by Averaging

Vocal attractiveness has a profound influence on listeners-a bias known as the "what sounds beautiful is good" vocal attractiveness stereotype [1]-with tangible impact on a voice owner's success at mating, job applications, and/or elections. The prevailing view holds that attractive voices are those that signal desirable attributes in a potential mate [2-4]-e.g., lower pitch in male voices. However, this account does not explain our preferences in more general social contexts in which voices of both genders are evaluated. Here we show that averaging voices via auditory morphing [5] results in more attractive voices, irrespective of the speaker's or listener's gender. Moreover, we show that this phenomenon is largely explained by two independent by-products of averaging: a smoother voice texture (reduced aperiodicities) and a greater similarity in pitch and timbre with the average of all voices (reduced "distance to mean"). These results provide the first evidence for a phenomenon of vocal attractiveness increases by averaging, analogous to a well-established effect of facial averaging [6, 7]. They highlight prototype-based coding [8] as a central feature of voice perception, emphasizing the similarity in the mechanisms of face and voice perception.