Vocal Fold Length Research Articles

Human Speech: A Restricted Use of the Mammalian Larynx

Speech has been hailed as unique to human evolution. Although the inventory of distinct sounds producible with vocal tract articulators is a great advantage in human oral communication, it is argued here that the larynx as a sound source in speech is limited in its range and capability because a low fundamental frequency is ideal for phonemic intelligibility and source-filter independence. Four existing data sets were combined to make an argument regarding exclusive use of the larynx for speech: (1) range of fundamental frequency, (2) laryngeal muscle activation, (3) vocal fold length in relation to sarcomere length of the major laryngeal muscles, and (4) vocal fold morphological development. Limited data support the notion that speech tends to produce a contracture of the larynx. The morphological design of the human vocal folds, like that of primates and other mammals, appears to be optimized for vocal communication over distances for which higher fundamental frequency, higher intensity, and fewer unvoiced segments are used. The positive message is that raising one's voice to call, shout, or sing, or executing pitch glides to stretch the vocal folds, can counteract this trend toward a contracted state.

Predicting Achievable Fundamental Frequency Ranges in Vocalization Across Species.

Vocal folds are used as sound sources in various species, but it is unknown how vocal fold morphologies are optimized for different acoustic objectives. Here we identify two main variables affecting range of vocal fold vibration frequency, namely vocal fold elongation and tissue fiber stress. A simple vibrating string model is used to predict fundamental frequency ranges across species of different vocal fold sizes. While average fundamental frequency is predominantly determined by vocal fold length (larynx size), range of fundamental frequency is facilitated by (1) laryngeal muscles that control elongation and by (2) nonlinearity in tissue fiber tension. One adaptation that would increase fundamental frequency range is greater freedom in joint rotation or gliding of two cartilages (thyroid and cricoid), so that vocal fold length change is maximized. Alternatively, tissue layers can develop to bear a disproportionate fiber tension (i.e., a ligament with high density collagen fibers), increasing the fundamental frequency range and thereby vocal versatility. The range of fundamental frequency across species is thus not simply one-dimensional, but can be conceptualized as the dependent variable in a multi-dimensional morphospace. In humans, this could allow for variations that could be clinically important for voice therapy and vocal fold repair. Alternative solutions could also have importance in vocal training for singing and other highly-skilled vocalizations.

Age- and sex-related variations in vocal-tract morphology and voice acoustics during adolescence

Distinct differences in the human voice emerge during adolescence, with males producing deeper and more resonant voices than females by the end of sexual maturation. Using magnetic resonance images of heads and voice recordings obtained in 532 typically developing adolescents, we investigate what might be the drivers of this change in voice, and the subjective judgment of the voice “maleness” and “femaleness”.We show clear sex differences in the morphology of voice-related structures during adolescence, with males displaying strong associations between age (and puberty) and both vocal-fold and vocal-tract length; this was not the case in female adolescents. At the same time, males (compared with females) display stronger associations between age (and puberty) with both fundamental frequency and formant position. In males, vocal morphology was a mediator in the relationship between bioavailable testosterone and acoustic indices.Subjective judgment of the voice sex could be predicted by the morphological and acoustic parameters in males only: the length of vocal folds and its acoustic counterpart, fundamental frequency, is a larger predictor of subjective “maleness” of a voice than vocal-tract length and formant position.

The postnatal ontogeny of the sexually dimorphic vocal apparatus in goitred gazelles (Gazella subgutturosa).

This study quantitatively documents the progressive development of sexual dimorphism of the vocal organs along the ontogeny of the goitred gazelle (Gazella subgutturosa). The major, male-specific secondary sexual features, of vocal anatomy in goitred gazelle are an enlarged larynx and a marked laryngeal descent. These features appear to have evolved by sexual selection and may serve as a model for similar events in male humans. Sexual dimorphism of larynx size and larynx position in adult goitred gazelles is more pronounced than in humans, whereas the vocal anatomy of neonate goitred gazelles does not differ between sexes. This study examines the vocal anatomy of 19 (11 male, 8 female) goitred gazelle specimens across three age-classes, that is, neonates, subadults and mature adults. The postnatal ontogenetic development of the vocal organs up to their respective end states takes considerably longer in males than in females. Both sexes share the same features of vocal morphology but differences emerge in the course of ontogeny, ultimately resulting in the pronounced sexual dimorphism of the vocal apparatus in adults. The main differences comprise larynx size, vocal fold length, vocal tract length, and mobility of the larynx. The resilience of the thyrohyoid ligament and the pharynx, including the soft palate, and the length changes during contraction and relaxation of the extrinsic laryngeal muscles play a decisive role in the mobility of the larynx in both sexes but to substantially different degrees in adult females and males. Goitred gazelles are born with an undescended larynx and, therefore, larynx descent has to develop in the course of ontogeny. This might result from a trade-off between natural selection and sexual selection requiring a temporal separation of different laryngeal functions at birth and shortly after from those later in life. J. Morphol. 277:826-844, 2016. © 2016 Wiley Periodicals, Inc.

Configuration of vocal folds during and after tube phonation in patients with voice disorders: A computerized tomographic study

Purpose: The study aims to observe whether any systematic change in vocal fold configuration occurs during and after phonation into a tube using computerized tomography (CT). Materials and Methods: Ten participants diagnosed with functional dysphonia were included in the study. CT was performed when participants produced the sound (a:), phonated into a drinking straw and when repeating (a:) after the exercise. Similar procedure was performed with a stirring straw after 20 min of vocal rest. Anatomic variables included: (1) glottal area, (2) glottal width, (3) vertical vocal fold thickness, (4) vocal fold area, and (5) vocal fold length. Each vocal fold was separately analyzed. Results: Only glottal area for stirring straw was statistically different throughout the three time points. This variable increased during tube phonation compared to conditions pre- and post-tube. Discussion: Since vocal fold length did not change during tube phonation, the increment in glottal area was likely due to increased amplitude of vibration. Increased vibratory amplitude has been found in previous studies with high-speed imaging, suggesting an increased subglottic pressure. From the physiologic point of view, transglottal pressure plays an important role in vocal fold amplitude of vibration. Conclusions: Tube phonation seems to cause increased glottal area during exercise. This change is more prominent during exercise with a higher degree of airflow resistance. Therefore, the degree of flow resistance is an important clinical variable to be considered when choosing the right voice exercises regarding the voice status/phonatory pattern of patients during voice therapy.

Interrater Reliability in Analysis of Laryngoscopic Features for Unilateral Vocal Fold Paresis

The diagnosis of paresis in patients with vocal fold motion impairment remains a challenge. In particular, laryngoscopy examination may result in significant disagreement in diagnosis among providers. We hypothesize that systematically evaluating for a standard set of clinical parameters will increase the diagnostic concordance among providers. Prospective case series conducted at a Tertiary referral Laryngology office. Two laryngologists (rater 1) and two trainees (rater 2) rated laryngoscopy findings in 19 patients suspected of paresis. The diagnosis was confirmed with laryngeal electromyogram. A standard set of 27 ratings was used for each examination that included movement, laryngeal configuration, and stroboscopy signs. A kappa coefficient was calculated for agreement in laryngoscopy findings and effectiveness in predicting the laterality of paresis. A substantial agreement (kappa coefficient>0.61) existed between the raters for vocal fold length, vocal fold thickness, bowing, and reduction in movement. A moderate agreement (kappa coefficient>0.41) existed between raters for piriform opening and reduced kinesis. The senior author was accurately able to diagnose the side of paresis in 89.5% of cases for a kappa coefficient of 0.78, whereas the trainees correctly predicted the side of paresis in 63.1% for a kappa coefficient of 0.35. The raters agreed on the diagnosis in 73.7% of cases for a kappa coefficient of 0.50. Using a standard set of laryngoscopy findings may improve the provider's ability to identify the laterality of vocal fold paresis and increase interrater reliability compared with other series.

A Preliminary Quantitative Comparison of Vibratory Amplitude Using Rigid and Flexible Stroboscopic Assessment

The purpose of this study was to establish preliminary, quantitative data on amplitude of vibration during stroboscopic assessment in healthy speakers with normal voice characteristics. Amplitude of vocal fold vibration is a core physiological parameter used in diagnosing voice disorders, yet quantitative data are lacking to guide the determination of what constitutes normal vibratory amplitude. Eleven participants were assessed during sustained vowel production using rigid and flexible endoscopy with stroboscopy. Still images were extracted from digital recordings of a sustained /i/ produced at a comfortable pitch and loudness, with F0 controlled so that levels were within ±15% of each participant's comfortable mean level as determined from connected speech. Glottal width (GW), true vocal fold (TVF) length, and TVF width were measured from still frames representing the maximum open phase of the vibratory cycle. To control for anatomic and magnification differences across participants, GW was normalized to TVF length. GW as a ratio of TVF width was also computed for comparison with prior studies. Mean values and standard deviations were computed for the normalized measures. Paired t tests showed no significant differences between rigid and flexible endoscopy methods. Interrater and intrarater reliability values for raw measurements were found to be high (0.89-0.99). These preliminary quantitative data may be helpful in determining normality or abnormality of vocal fold vibration. Results indicate that quantified amplitude of vibration is similar between endoscopic methods, a clinically relevant finding for individuals performing and interpreting stroboscopic assessments.

Use Videostrobokymography to Quantitatively Analyze the Vibratory Characteristics Before and After Conservative Medical Treatment of Vocal Fold Leukoplakia

To quantitatively analyze the vibratory characteristics of vocal folds before and after conservative treatments to evaluate the outcomes of conservative treatments for vocal fold leukoplakia using videostrobokymography (VSK). This is a prospective study. Twenty patients and 20 controls were enrolled into the study. All patients received conservative treatments for 3weeks and received VSK examination before and 3weeks after the treatments. All controls only received VSK examination once. Vocal fold lengths of 25%, 50%, and 75% were chosen as the line-scan positions to evaluate the vocal fold vibration. Open quotient (OQ) and asymmetry index (AI) were obtained using VSK. Significant improvements in the main symptoms including voice hoarseness were found. Videostroboscopic findings showed that the white lesions on the vocal folds almost completely disappeared in all patients, and the vocal fold flexibility returned to normal. All OQs and AIs at each line-scan position in patients before the treatments were larger than those in controls (P<0.017), whereas all OQs and AIs at each line-scan position decreased 3weeks after conservative treatments (P<0.017). No significant differences in OQs and AIs at each line-scan position were detected between patients after the treatments and controls (P > 0.017). VSK could quantitatively evaluate the vibratory characteristics of vocal folds before and after the treatments, and conservative treatment could improve VSK measurements to normal control values, suggesting that VSK is a tool to assess the outcomes of the conservative treatments for vocal fold leukoplakia.

Vocal Fold Adjustment Caused by Phonation Into a Tube: A Double-Case Study Using Computed Tomography

Phonation into a tube is a widely used method for vocal training and therapy. Previous studies and practical experience show that the phonation becomes easier and louder after such an exercise. The purpose of this study was to find out whether there are systematic changes in the vocal fold adjustment after the exercise. Two volunteer subjects (1 male and 1 female) without voice disorders were examined with computed tomography (CT). Both produced a sustained vowel [a:] at comfortable pitch and loudness before and after the tube phonation and a vowel-like phonation into the tube. Computed tomography (CT) scans were obtained before, during, and after the exercise, twice for each condition. The gathered CT images were used for measurements of vertical vocal fold thickness, bulkiness, length, and glottal width. No prominent trends common to both subjects were found in vocal fold adjustment during and after the phonation into the tube. Variability observed under the same conditions was usually of the same magnitude as the changes before and after the tube phonation. Changes in vocal tract configuration observed after the resonance tube exercises in previous related studies were more prominent than the changes in vocal fold configuration observed here.

The Effect of Inspiration and Phonation on Vocal Fold Length

The detection of metric dimensions of laryngeal structures yielded valuable information for both clinical and research purposes. The aim of this paper was to evaluate the absolute dimensions of true vocal fold length (TVFL) during inspiration and phonation with a stroboscope coupling with laser equipment. Forty graduate student subjects including 20 males and 20 females were examined. The measurements were made during inspiration and phonation at a fixed fundamental frequency within each participant. The maximal TVFL was got from the inspiration and the minimal from the phonation. Results showed that the mean values of male inspiration and phonation TVFL were 12.81 + 2.97 mm and 10.92 + 4.40 mm respectively. While in female, they were 11.27 + 2.71 mm and 7.16 + 2.65 mm respectively. There was statistically significant between inspiration and phonation TVFL in the female group. In female, TVFL at phonation was significantly shortened than in male. We concluded stroboscope coupling with laser projection marking module could be used to assess physiological variation of TVFL. This technique enabled the detection of absolute spatial laryngeal dimensions, which was useful in providing valuable information in diagnostics and interpretation of voice disorders.

Functional morphology of the Alligator mississippiensis larynx with implications for vocal production.

Sauropsid vocalization is mediated by the syrinx in birds and the larynx in extant reptiles; but whereas avian vocal production has received much attention, the vocal mechanism of basal reptilians is poorly understood. The American alligator (Alligator mississippiensis) displays a large vocal repertoire during mating and in parent-offspring interactions. Although vocal outputs of these behaviors have received some attention, the underlying mechanism of sound production remains speculative. Here, we investigate the laryngeal anatomy of juvenile and adult animals by macroscopic and histological methods. Observations of the cartilaginous framework and associated muscles largely corroborate earlier findings, but one muscle, the cricoarytenoideus, exhibits a heretofore unknown extrinsic insertion that has important implications for effective regulation of vocal fold length and tension. Histological investigation of the larynx revealed a layered vocal fold morphology. The thick lamina propria consists of non-homogenous extracellular matrix containing collagen fibers that are tightly packed below the epithelium but loosely organized deep inside the vocal fold. We found few elastic fibers but comparatively high proportions of hyaluronan. Similar organizational complexity is also seen in mammalian vocal folds and the labia of the avian syrinx: convergent morphologies that suggest analogous mechanisms for sound production. In tensile tests, alligator vocal folds demonstrated a linear stress-strain behavior in the low strain region and nonlinear stress responses at strains larger than 15%, which is similar to mammalian vocal fold tissue. We have integrated morphological and physiological data in a two-mass vocal fold model, providing a systematic description of the possible acoustic space that could be available to an alligator larynx. Mapping actual call production onto possible acoustic space validates the model's predictions.

Evaluation of True Vocal Fold Growth as a Function of Age

Objectives: Evaluate change in true vocal fold length as function of age. Methods: Prospective study at tertiary aerodigestive center between 2011 and 2013. A total of 205 patients (ages 1 month to 20 years), of which 87 (42.4%) were female and 118 (57.6%) male, were included. Lengths of total vocal fold (TVFL), membranous vocal fold (MVFL), and cartilaginous vocal fold (CVFL) were measured during direct laryngoscopy. Membranous-to-cartilaginous ratios (M/C) were calculated. Results: Mean MVFL under age 1 year for females was 4.4 ± 1.3 mm and for males 4.9 ± 1.8 mm. At age 17 years, mean MVFL was 12.3 ± 2.1 mm for females and 14.0 ± 1.4 mm for males. Mean TVFL, MVFL, and CVFL increased 0.7 mm, 0.5 mm, and 0.2 mm per year in linear fashion, respectively (linear regression, P &lt; .0001). M/C ratio did not significantly change with age ( P = .78). Mean TVFL, MVFL, and CVFL showed trend of being longer in males than females, but these did not reach statistical significance ( P = .27; .11; .75, respectively). Conclusions: This is the largest longitudinal pediatric study specifically examining vocal fold length as function of age. Each length of true vocal fold appears to linearly increase for both females and males. M/C ratio remained relatively constant unlike previously reported data, possibly due to in vivo versus cadaveric measurements. These findings suggest critical periods of development in females and males are not explainable by changes in vocal fold length alone, and other factors such as vocal fold layers (linear density) need further exploration.

Evaluation of true vocal fold growth as a function of age.

To evaluate change in true vocal fold length as a function of age. Prospective study. Tertiary aerodigestive center. In total, 205 patients (aged 1 month to 20 years), of whom 87 (42.4%) were female and 118 (57.6%) male, were included. Lengths of the total vocal fold (TVFL), membranous vocal fold (MVFL), and cartilaginous vocal fold (CVFL) were measured during direct laryngoscopy. Membranous-to-cartilaginous (M/C) ratios were calculated. For patients younger than 1 year, mean (SD) MVFL was 4.4 (1.3) mm for females and 4.9 (1.8) mm for males. At age 17 years, mean (SD) MVFL was 12.3 (2.1) mm for females and 14.0 (1.4) mm for males. Mean TVFL, MVFL, and CVFL increased an average of 0.7 mm, 0.5 mm, and 0.2 mm per year in linear fashion, respectively (linear regression, P < .0001). The M/C ratio did not significantly change with age (P = .33). Mean TVFL, MVFL, and CVFL showed no statistical difference between males and females (P = .27, .11, and .75, respectively). This is the largest longitudinal pediatric study specifically examining vocal fold length as a function of age. Each length of the true vocal fold appeared to linearly increase for both females and males. The M/C ratio remained relatively constant, unlike previously reported data, possibly due to in vivo vs cadaveric measurements. These findings suggest that critical periods of development in females and males are not explainable by changes in vocal fold length alone, and other factors such as vocal fold layers need further exploration.

Pitch Elevation in Trangendered Patients: Anterior Glottic Web Formation Assisted by Temporary Injection Augmentation

Pitch elevation surgery is most often indicated to assist male-to-female transgendered individuals seeking a more feminine voice quality. Behavioral therapy is primary management but if the desired voice quality is not achieved, surgery is offered. Procedures described that raise vocal pitch alter one or more of the main parameters known to physiologically control pitch; vocal fold tension, length, and mass. Web formation with injection augmentation significantly raises vocal pitch in male-to-female transgendered individuals. Retrospective cohort study. This report describes the voice results after anterior web formation with injection augmentation to reduce vocal fold length in a series of 10 transgendered patients. Retrospective review of male-to-female transgendered patients referred to St. Michaels Hospital Voice Clinic, Toronto, Canada for pitch elevation was carried out including demographic data, preoperative and postoperative acoustic data and videostroboscopic evaluation. Comparison between preoperative to postoperative acoustic measures demonstrated a mean increase in fundamental frequency of 110Hz after web formation. Perturbation measures and pitch range were unchanged from before surgery to after surgery. This novel modification for endoscopic anterior web formation has been shown to be a successful procedure for permanent elevation of pitch with little or no morbidity.

Computational Study of Effects of Tension Imbalance on Phonation in a Three-Dimensional Tubular Larynx Model

The present study explores the use of a continuum-based computational model to investigate the effect of left-right tension imbalance on vocal fold (VF) vibrations and glottal aerodynamics, as well as its implication on phonation. The study allows us to gain new insights into the underlying physical mechanism of irregularities induced by VF tension imbalance associated with unilateral cricothyroid muscle paralysis. A three-dimensional simulation of glottal flow and VF dynamics in a tubular laryngeal model with tension imbalance was conducted by using a coupled flow-structure interaction computational model. Tension imbalance was modeled by reducing by 20% the Young's modulus of one of the VFs, while holding VF length constant. Effects of tension imbalance on vibratory characteristic of the VFs and on the time-varying properties of glottal airflow as well as the aerodynamic energy transfer are comprehensively analyzed. The analysis demonstrates that the continuum-based biomechanical model can provide a good description of phonatory dynamics in tension imbalance conditions. It is found that although 20% tension imbalance does not have noticeable effects on the fundamental frequency, it does lead to a larger glottal flow leakage and asymmetric vibrations of the two VFs. A detailed analysis of the energy transfer suggests that the majority of the energy is consumed by the lateral motion of the VFs and the net energy transferred to the softer fold is less than the one transferred to the normal fold.

Comparison of benign lesion regression following vocal fold steroid injection and vocal hygiene education

This study intends to objectively quantify and compare the regression rates of vocal lesions in patients receiving either vocal fold steroid injection (VFSI) or vocal hygiene education (VHE). Potential influence of occupational vocal demands on the treatment outcome was also investigated. Retrospective case series. This study enrolled 176 patients of vocal nodules and vocal polyps. Ninety-two patients received VFSI, while 84 patients received VHE. We measured the lesion area with correction by the length of vocal fold, according to videolaryngoscopic examinations before treatment and 1 and 2 months after treatment. VFSI was associated with a higher lesion reduction rate than VHE at 1 and 2 months (P <0.05). In vocal nodules and patients with ordinary occupational vocal demands, VFSI achieved a higher lesion regression rate than VHE at 1 month (P <0.05), while both modalities resulted in similar lesion reduction rates at 2 months (P >0.05). In vocal polyps, the lesion reduction rate after VFSI was higher than that following VHE at 1 and 2 months (P <0.01). In patients with high occupational vocal demands, the lesion sizes decreased significantly at 1 and 2 months following VFSI (P <0.01), but not for those receiving VHE (P >0.05). VHE remains the fundamental strategy for all dysphonic patients, while VFSI can be applied alternatively. Both VFSI and VHE are effective for vocal nodules and patients with ordinary occupational vocal demands, but VFSI achieves lesion regression earlier than VHE. VFSI is preferred over VHE for vocal polyps and patients with high occupational vocal demands. 4.

An Anatomic Study of the Suspensory Ligaments of the Anterior Commissure

Objectives: Delineate the location and anterior/posterior and superior/inferior orientation of the suspensory ligaments of the anterior commissure attachment of the vocal folds in order to characterize how much of the laryngeal cartilage may be safely removed for aesthetic or oncologic purposes without compromising vocal function. Methods: Study design: anatomic dissection of cadaver larynges. Preserved cadaver larynges were dissected with careful attention to ligamentous attachments to the laryngeal framework of the vocal folds. AP and superior/inferior relationships are described. Removal of various amounts of cartilage around the anterior commissure was correlated with vocal fold length and tension. Results: Our results help to characterize the extent to which laryngeal framework may be removed around the anterior commissure while maintaining vocal fold support. Conclusions: These data may help surgeons to better understand the degree of laryngeal cartilage that may be safely removed in situations of oncologic resection, aesthetic intervention (eg, aesthetic chondrolaryngoplasty), or post-traumatic reconstruction.

In Vivo Measurement of Pediatric Vocal Fold Motion Using Structured Light Laser Projection

The aim of the study was to present the development of a miniature structured light laser projection endoscope and to quantify vocal fold length and vibratory features related to impact stress of the pediatric glottis using high-speed imaging. The custom-developed laser projection system consists of a green laser with a 4-mm diameter optics module at the tip of the endoscope, projecting 20 vertical laser lines on the glottis. Measurements of absolute phonatory vocal fold length, membranous vocal fold length, peak amplitude, amplitude-to-length ratio, average closing velocity, and impact velocity were obtained in five children (6-9 years), two adult male and three adult female participants without voice disorders, and one child (10 years) with bilateral vocal fold nodules during modal phonation. Independent measurements made on the glottal length of a vocal fold phantom demonstrated a 0.13mm bias error with a standard deviation of 0.23mm, indicating adequate precision and accuracy for measuring vocal fold structures and displacement. First, invivo measurements of amplitude-to-length ratio, peak closing velocity, and impact velocity during phonation in pediatric population and a child with vocal fold nodules are reported. The proposed laser projection system can be used to obtain invivo measurements of absolute length and vibratory features in children and adults. Children have large amplitude-to-length ratio compared with typically developing adults, whereas nodules result in larger peak amplitude, amplitude-to-length ratio, average closing velocity, and impact velocity compared with typically developing children.

Differentiating arytenoid dislocation and recurrent laryngeal nerve paralysis by arytenoid movement in laryngoscopic video.

To present a new method of quantifying arytenoid movement during inspiration and determine if it can be used to distinguish arytenoid dislocation from vocal fold paralysis. Case series with chart review. Retrospective study conducted in a university laboratory based on university hospital data. Endoscopic videos from 8 patients with dislocation and 5 patients with vocal fold paralysis diagnosed by electromyography were included. Vector analysis measured cuneiform movement, an indirect measurement of arytenoid movement, during 1 inspiration. Measurements normalized and not normalized to vocal fold length were evaluated. Interrater reliability (2 raters) and intrarater reliability (1 rater performing the analysis twice) were evaluated using intraclass correlation coefficient (ICC) analysis. Raters were blinded to subject group during analysis. Pixel-valued cuneiform movement was 81.16 ± 25.62 for dislocation and 30.22 ± 23.60 for paralysis (P = .019). Unitless cuneiform movement was 0.58 ± 0.17 for dislocation and 0.24 ± 0.18 for paralysis (P = .030). Interrater ICC was 0.942 for pixel-valued measurements and 0.962 for unitless measurements. Intrarater ICC was 0.909 for pixel-valued measurements and 0.881 for unitless measurements. Both pixel-valued and unitless measures of arytenoid movement were significantly greater in arytenoid dislocation than vocal fold paralysis. Pixel-valued measurements were included to demonstrate the ability to make quantitative comparisons across subjects without precise knowledge of camera precision, provided position is approximately stable, as each measurement is inherently normalized by vocal tract length. Future studies will apply this new method of evaluating vocal fold immobility disorders on a larger scale and incorporate a more diverse group of etiologies.

Physiologic and Acoustic Patterns of Essential Vocal Tremor

This article describes a case study of physiologic and acoustic patterns of essential vocal tremor (EVT). Simulations of vocal tremor were used to test hypotheses regarding measured acoustic patterns and expected physiologic sources. This is a case study of EVT using an analysis by synthesis approach. Oscillations of vocal tract and laryngeal structures were identified using rigid videostroboscopic examination. Acoustical analyses of sustained phonation were completed using the methods previously described in the literature and custom-written MATLAB functions. Simulations of the client's vocal tremor were created using a computational model. The client exhibited vocal fold length changes and oscillation within the laryngeal vestibule during sustained phonation at a comfortable pitch and loudness. Despite the involvement of vocal fold length changes, a low average extent of fundamental frequency (F0) modulation (ie, 5.3%) and high average extent of intensity modulation (ie, 23.0%) were measured. Simulations of vocal tremor involving modulation of F0 demonstrated that this source of tremor contributes to frequency-induced intensity modulation, although there was a greater extent of F0 modulation than intensity modulation. The greater extent of intensity than F0 modulation in one client with EVT exhibiting predominant vocal fold length changes contrasted with the lower extent of intensity than F0 modulation in simulated vocal tremor involving F0 modulation. These findings demonstrate that other potential sources of intensity modulation outside the larynx should be determined during the evaluation of clients with vocal tremor.