Changes In Voice Quality Research Articles

Impact of vocal tract resonance on the perception of voice quality changes caused by vocal fold stiffness

Experiments using animal and human larynx models are often conducted without a vocal tract. While it is reasonable to assume the absence of a vocal tract has only small effects on vocal fold vibration, it is unclear how sound production and its perception will be affected. In this study, the validity of using data obtained in the absence of a vocal tract for voice perception studies was investigated. Using a two-layer self-oscillating physical model, three series of voice stimuli were created: one produced with conditions of left-right symmetric vocal fold stiffness, and two with left-right asymmetries in vocal fold body stiffness. Each series included a set of stimuli created with a physical vocal tract, and a second set created without a physical vocal tract. Stimuli were re-synthesized to equalize the mean F0 for each series and normalized for amplitude. Listeners were asked to evaluate the three series in a sort-and-rate task. Multidimensional scaling analysis will be applied to examine the perceptual interaction between the voice source and the vocal tract resonances. [Work supported by NIH.]

Análise da qualidade vocal antes e após o uso profissional e social da voz

Objetivo Analisar, do ponto de vista perceptivo-auditivo, os efeitos do uso profissional e social da voz na qualidade vocal de mulheres, em um intervalo de tempo de duas horas e 30 minutos. Métodos Pesquisa do tipo caso-controle, formada por dois grupos: grupo de uso profissional da voz, com 31 professoras, faixa etária de 28 a 59 anos e grupo de uso social da voz, com 42 mulheres, faixa etária de 31 a 59 anos, sem o uso profissional da voz e sem queixa vocal. A coleta foi realizada pela manhã, em dois momentos - antes da primeira aula e após duas horas e 30 minutos -, na própria escola em que as professoras lecionavam e consistiu em leitura de frases. O grupo de uso social seguiu os mesmos padrões de gravação, com uso da voz na residência de cada participante. As vozes foram avaliadas de forma perceptivo-auditiva por dois avaliadores experientes, comparando-se as emissões antes e após o uso e classificação de melhora, piora ou similaridade entre os momentos. Resultados Os grupos não apresentaram diferenças entre as vozes, comparando-se os momentos antes e após o uso da voz. Nos casos em que houve modificação do padrão vocal, a rugosidade foi o parâmetro perceptivo-auditivo mais frequente nos dois grupos, porém com baixo grau de alteração. Conclusão O uso social e o uso profissional da voz, decorrente da atividade letiva, no período de duas horas e 30 minutos, não causaram alterações na qualidade vocal, analisada de forma perceptivo-auditiva.

Microsurgical Release of the Cover and Fibrin Glue Implantation for Treatment of Sulcus and Scars

Objectives: Sulcus vocalis and scars of the vocal folds reduce pliability of the cover impairing vibration. Severity of dysphonia is directly related to magnitude of structural damage. The purpose of surgical treatment is to restore anatomy in order to re-establish function. The aim of the study was to evaluate the effectiveness of microsurgical liberation of scars and placement of fibrin glue implants into the subepithelial space of the vocal folds to improve pliability. Methods: Fifteen patients (age range, 13-69 years) with diagnosis of sulcus and/or scars were classified into 3 groups, according to severity of structural damage: Group 1: Unilateral, localized lesions with minimal subepithelial compromise. Group 2: Sulcus and/or scars with subepithelial fibrosis. Group 3: Severe scarring. Microsurgical liberation of scar tissue and placing of fibrin glue implants were performed. Fibrin glue components are mixed until solidified. An implant is tailored and it is placed into the subepithelial space. All patients were evaluated preoperatively and postoperatively with stroboscopy. Voice quality changes were assessed by means of the Voice Handicap Index 30 questionnaire. Results: The technique offered significant vibratory pattern and voice quality improvement in group one and better vibratory pattern and moderate voice quality improvement in group 2. In group 3, although some vibratory improvement was achieved, voice quality results were not satisfactory in 4 out of 5 patients. Conclusions: The technique described is useful for treatment of vibratory impairment caused by sulcus and/or scarring of the vocal folds in which structural damage is limited. In extensive lesions results show little improvement.

Modern Approaches in Injuries of the Larynx

Introduction: Early diagnosis and proper treatment of laryngeal trauma is of great importance for the patient to prevent the formation of stenosis in a later stage, changes in breathing and voice quality. Material and methods: The covered laryngeal trauma is a relatively rare injury. Its incidence is estimated at 1 in 30,000 visits to emergency rooms. Results: Due to their relatively low frequency and association with other life-threatening injuries, laryngeal trauma often go unrecognized. This is bad because the glottis laryngeal stenosis and insufficiency are the end result of delayed or inadequate treatment of laryngeal trauma. Conclusion: Despite the great variety of these injuries, correct diagnosis and understanding of each case justify the adoption of a standardized method for classifying and treating these injuries. These preconditions will facilitate successful therapy.

Ventricular-Fold Dynamics in Human Phonation

In this study, the authors aimed (a) to provide a classification of the ventricular-fold dynamics during voicing, (b) to study the aerodynamic impact of these motions on vocal-fold vibrations, and (c) to assess whether ventricular-fold oscillations could be sustained by aerodynamic coupling with the vocal folds. A 72-sample database of vocal gestures accompanying different acoustical events comprised high-speed cinematographic, audio, and electroglottographic recordings of 5 subjects. Combining the physiological correlates with a theoretical model of phonation, the vocal-ventricular aerodynamic interactions were investigated. A ventricular-fold motion is found during (de)crescendos, shout, throat singing, yodel, growls, and glides with transitions between registers. Three main types of dynamics are identified: slow nonoscillatory motion and fast oscillatory motion with aperiodical or periodical vibrations. These patterns accompany a change in voice quality, pitch, and/or intensity. Alterations of glottal-oscillatory amplitude, frequency, and contact were predicted. It is shown that a ventricular oscillation can be initiated and sustained by aerodynamic coupling with the vocal folds. Vocal-ventricular aerodynamic interactions can alter, enhance, or suppress vocal-fold vibrations or leave them unchanged, depending on the ventricular-fold dynamics involved. Depending on its variation in time, a similar level of ventricular-fold adduction impacts the glottal vibratory magnitude and contact much differently.

Effect of Weight Loss on Voice After Bariatric Surgery

To investigate the effect of weight loss on voice. Prospective study. A total of 15 subjects undergoing bariatric surgery were investigated. Six subjects were lost to follow-up, and nine subjects were evaluated preoperatively and 3-6months postoperatively. The evaluation included a questionnaire on voice quality filled by the patient, laryngeal examination, perceptual evaluation, and acoustic analysis. The questionnaire consisted of four questions: change in vocal pitch, change in vocal loudness, increase or decrease in phonatory effort, and the presence or absence of vocal fatigue. For the perceptual evaluation, a simplified version of the Grade, Roughness, Breathiness, Asthenia, Strain scale classification was used. These parameters were rated using a score ranging from zero to three where zero stands for none and three for severe. For the acoustic analysis, the following variables were measured: fundamental frequency, habitual pitch, jitter, shimmer, noise-to-harmonics ratio, voice turbulence index, and maximum phonation time. The mean age was 35.56±9.93years. The mean weight preoperatively and postoperatively was 112.17 and 83.61kg, respectively. The body mass index dropped by eight points from 38.06 to 30.83. Only three of the nine patients have reported change in voice quality. The latter was described as an increase in vocal pitch in the three cases, reduced loudness and increased phonatory effort in two, and the presence of vocal fatigue in one. There was no significant difference in the mean score of any of the perceptual parameters in patients preoperatively versus postoperatively. There was also no significant difference in any of the acoustic parameters or in the laryngeal findings before and after surgery. One-third of the patients with weight loss reported change in voice quality that was not documented acoustically. The laryngeal examination is nonrevealing.

Patient-Reported Voice and Speech Outcomes After Whole-Neck Intensity Modulated Radiation Therapy and Chemotherapy for Oropharyngeal Cancer: Prospective Longitudinal Study

To describe voice and speech quality changes and their predictors in patients with locally advanced oropharyngeal cancer treated on prospective clinical studies of organ-preserving chemotherapy-intensity modulated radiation therapy (chemo-IMRT). Ninety-one patients with stage III/IV oropharyngeal cancer were treated on 2 consecutive prospective studies of definitive chemoradiation using whole-field IMRT from 2003 to 2011. Patient-reported voice and speech quality were longitudinally assessed from before treatment through 24 months using the Communication Domain of the Head and Neck Quality of Life (HNQOL-C) instrument and the Speech question of the University of Washington Quality of Life (UWQOL-S) instrument, respectively. Factors associated with patient-reported voice quality worsening from baseline and speech impairment were assessed. Voice quality decreased maximally at 1 month, with 68% and 41% of patients reporting worse HNQOL-C and UWQOL-S scores compared with before treatment, and improved thereafter, recovering to baseline by 12-18 months on average. In contrast, observer-rated larynx toxicity was rare (7% at 3 months; 5% at 6 months). Among patients with mean glottic larynx (GL) dose ≤20 Gy, >20-30 Gy, >30-40 Gy, >40-50 Gy, and >50 Gy, 10%, 32%, 25%, 30%, and 63%, respectively, reported worse voice quality at 12 months compared with before treatment (P=.011). Results for speech impairment were similar. Glottic larynx dose, N stage, neck dissection, oral cavity dose, and time since chemo-IMRT were univariately associated with either voice worsening or speech impairment. On multivariate analysis, mean GL dose remained independently predictive for both voice quality worsening (8.1%/Gy) and speech impairment (4.3%/Gy). Voice quality worsening and speech impairment after chemo-IMRT for locally advanced oropharyngeal cancer were frequently reported by patients, underrecognized by clinicians, and independently associated with GL dose. These findings support reducing mean GL dose to as low as reasonably achievable, aiming at ≤20 Gy when the larynx is not a target.

Características vocais e emocionais de professores e não professores com baixa e alta ansiedade

Objetivo Comparar características vocais e emocionais em grupos de professores e não professores com baixa e alta ansiedade. Métodos Participaram do estudo 93 sujeitos, de ambos os gêneros, com idades entre 18 e 59 anos, divididos em quatro grupos: professores com baixa ansiedade (PBA), professores com alta ansiedade (PAA), não professores com baixa ansiedade (NPBA) e não professores com alta ansiedade (NPAA). Os parâmetros vocais foram mensurados por meio dos instrumentos Questionário de Sinais e Sintomas Vocais (QSSV), Protocolo de Qualidade de Vida em Voz (QVV), Índice de Desvantagem Vocal (IDV), além da gravação de fala e vogal sustentada, avaliada por três fonoaudiólogos, a partir da Escala Analógico-Visual (EAV). Para avaliação dos parâmetros emocionais, utilizou-se o Self-Report Questionnaire (SRQ) e o Inventário de Ansiedade Traço-Estado (IDATE). Resultados Constatou-se que os grupos com alta ansiedade relataram sintomas indicativos de alto nível de estresse e depressão, sendo que o grupo de professores apresentou maior número de sintomas emocionais. Quanto aos parâmetros vocais, observou-se que os professores com alta ansiedade expressaram maior número de sintomas vocais, maior comprometimento da qualidade de vida em voz, maior desvio global da qualidade vocal e alto índice de desvantagem vocal, quando comparados com os demais grupos. Conclusão Os indivíduos com alta ansiedade tiveram maior comprometimento emocional, vocal e na qualidade de vida, sobretudo aqueles que têm a voz como instrumento de trabalho, os professores.

Changes in Voice Quality after Speech-Language Therapy Intervention in Older Children with Cerebral Palsy

Objective: We examined whether perceived voice quality is altered in a group of children with cerebral palsy (CP) following an intervention focusing on respiration and phonation, and whether possible improvements might be associated with increased intelligibility levels. Methods: Sixteen individuals with CP and dysarthria (9 girls, mean age 14 years, SD = 2; 9 with spastic type CP, 2 dyskinetic, 4 mixed, 1 Worster-Drought syndrome) completed intelligibility assessments on separate days twice before intervention, at termination of treatment and at 6-week follow-up using 50 words from the Children's Speech Intelligibility Measure lists, and describing cartoon strips. Experienced speech-language pathologists rated voice quality employing GRBAS scales. Results: There was no clear evidence that change in voice quality pre-post intervention was large compared with change in the pre-intervention or post-intervention periods. Asthenia demonstrated largest improvement (effect size of 0.4). Intelligibility correlated weakly with Grade, Breathiness and Asthenia, but not with Roughness or Strain. A deterioration of 1 unit on the Grade and Asthenia scales was associated with an approximately 11% decrease in intelligibility. Conclusion: Perceived changes in voice quality were small compared to changes in intelligibility. Further investigations must examine other variables potentially associated with intelligibility gain to better understand the links between the respiratory-phonatory intervention and improved intelligibility.

Change of Voice Quality before and after Treatment of Short-Term Therapy with Proton Pump Inhibitor in Laryngopharyngeal Reflux

Received May 19, 2014 Revised July 23, 2014 Accepted July 23, 2014 Address for correspondence Jung Hyun Chang, MD, PhD Department of OtolaryngologyHead and Neck Surgery, National Health Insurance Service Ilsan Hospital, 100 Ilsan-ro, Ilsandong-gu, Goyang 410-719, Korea Tel +82-31-900-0346 Fax +82-31-900-0613 E-mail manbang5@naver.com Background and ObjectivesZZThe aim of this study was to verify that voice analysis could be an alternate tool for the evaluation of proton pump inhibitor treatment of laryngopharyngeal reflux (LPR). Subjects and MethodZZTwenty-two patients with LPR symptoms underwent laryngoscopy, stroboscopy and their reflux finding index (RFI) were evaluated. Subjective reflux symptom scores (RSS) and voice handicap index (VHI) were completed at the baseline. All patients underwent voice analysis. Thereafter, patients had short-term proton pump inhibitor therapy for 6 weeks. The RFI, RSS, VHI and voice analysis were repeated during the last week of the treatment. ResultsZZRFI was improved and both RSS and VHI were improved after the treatment. RSS and VHI were significantly correlated. In voice analysis, shimmer significantly improved and harmony to noise ratio (HNR) also improved. ConclusionZZVoice analysis can be indicators of treatment results of laryngopharyngeal reflux disease. Korean J Otorhinolaryngol-Head Neck Surg 2014;57(10):703-6

Toward a unified theory of voice production and perception.

At present, two important questions about voice remain unanswered: When voice quality changes, what physiological alteration caused this change, and if a change to the voice production system occurs, what change in perceived quality can be expected? We argue that these questions can only be answered by an integrated model of voice linking production and perception, and we describe steps towards the development of such a model. Preliminary evidence in support of this approach is also presented. We conclude that development of such a model should be a priority for scientists interested in voice, to explain what physical condition(s) might underlie a given voice quality, or what voice quality might result from a specific physical configuration.

カラオケ歌唱による声質変化と水分摂取の関係

カラオケ歌唱による声質変化の有無，声質変化と水分摂取の関係を解明するため1） 16曲のカラオケ歌唱はその後の音声のjitter・shimmer・harmonic-to-noise ratio（HNR）に変化をもたらすか，2）カラオケ歌唱中の水分摂取の有無はカラオケ後の音声のjitter・shimmer・HNRの変化程度に差をもたらすかを検討した．その結果，16曲のカラオケ歌唱はその後の低い声と出しやすい声の高さの発声に影響を及ぼすことが示された．しかしVEによる喉頭所見では炎症や血腫等の著明な変化は見られず，カラオケ後の音響特徴の変化が血腫等に起因するものではない可能性が示唆された．また，声の高さやパラメータを通じた水分摂取の効果は見られなかったが，高い声での発声が水分摂取の有無に敏感である可能性が示唆された．

Is Vocal Cord Asymmetry Seen on Transcutaneous Laryngeal Ultrasonography a Significant Predictor of Voice Quality Changes After Thyroidectomy?

Vocal cord asymmetry (VCA) on laryngoscopic examination (LE) may suggest voice impairment after thyroidectomy, but LE may cause patient discomfort. We aimed to correlate the presence of postoperative VCA assessed by noninvasive transcutaneous laryngeal ultrasonography (TLUSG) with voice quality changes after thyroidectomy. A total of 169 patients scheduled for thyroidectomy completed two validated voice symptoms questionnaires-the GRBAS (grade, roughness, breathiness, asthenia, strain) scale and the voice impairment score (VIS)-and underwent TLUSG and LE at 1day before and 7-10days after thyroidectomy. Postoperative VCA was apparent in 51 patients on TLUSG (group I), whereas there was no VCA in the other 118 patients (group II, controls). The GRBAS scale and VIS results were compared between the groups. Before operation, the two groups had comparable preoperative GRBAS and VIS status. After operation, the "grade" and "roughness" components on the GRBAS scale were significantly worse in group I than in group II: 0.24 versus 0.07 (p=0.016) and 0.33 versus 0.14 (p=0.022), respectively. "Grade" and "roughness" in the GRBAS scale significantly worsened after the operation in group I: from 0.04 to 0.24 (p=0.008) and from 0.02 to 0.33 (p=0.001), respectively. They did not change in group II. Also, the overall VIS was significantly worse after thyroidectomy in group I: 4.97 versus 12.97 (p<0.001). VCA seen on TLUSG significantly correlated with "grade" and "roughness" components on the GRBAS scale and the overall VIS. Thus, VCA might be used as a surrogate of postoperative voice changes.

Acoustic, perceptual and aerodynamic voice evaluation in an obese population

To investigate perceptual, acoustic and aerodynamic voice parameters in obese individuals. Twenty obese and 20 normal-weight volunteers underwent voice evaluation by laryngoscopy, acoustic analysis, aerodynamic measurement and perceptual analysis (using the grade-roughness-breathiness-asthenia-strain ('GRBAS') scale and the Voice Handicap Index 10 scale). Data from both subject groups were compared. No difference was found in acoustic analysis parameters between the two groups (p > 0.05). Maximum phonation time in the obese group (mean ± standard deviation, 19.6 ± 4.9 seconds) was significantly shorter than in controls (26.4 ± 4.1 seconds) (p < 0.001), although the s/z ratio was very similar between the two groups. In the obese and control groups, the mean ± standard deviation grade-roughness-breathiness-asthenia-strain scores were 1 ± 1.3 and 0.2 ± 0.6 (p = 0.002) and the mean ± standard deviation Voice Handicap Index 10 scores were 0.5 ± 1.2 and 1.2 ± 1.7 (p = 0.27), respectively. Obese individuals had poorer vocal quality as judged by the grade-roughness-breathiness-asthenia-strain scale, and reduced maximum phonation time. However, there was no change in voice quality as assessed by acoustic analysis and Vocal Handicap Index 10 score, compared with controls.

DYSPHONIA IN PEDIATRIC PRACTICE: CAUSES AND METHODS OF TREATMENT

Causes of dysphonia in children and adolescents vary from genetic syndromes, congenital defects, diseases of various organs and systems and to non-observance of hygiene or voice overstrain. Complex examination can help to reveal such causes. Laryngeal endoscopy remains one of the most reliable methods of investigation, but non-invasive methods (acoustic voice analysis — AVA, electroglottography — EGG) are no less important. The more detailed specification of voice timbre disturbances (organic or functional, with psycho-emotional lability being the most common cause) can help choose the method of its correction. Complex homeopathic drugs are promising in treatment of dysphonia of various etiology in children. Aim: to assess reliability of non-invasive methods of voice examination (AVA and EGG) in treatment of functional dysphonia in children. Patients and methods: 100 patients with dysphonia aged from 3 to 15 years old were examined. All of them were performed laryngeal endoscopy, AVA and EGG. Results: both methods demonstrated reliable differences of characteristics, describing the quality of voice before and after the treatment. Conclusions: AVA and EGG reflect changes in voice quality during and after provided treatment (including complex homeopathic drugs) and can be used as unbiased criteria of treatment efficacy assessment.

External laryngeal injuries in children—Comparison of diagnostic methods

ObjectivesThe injuries of the larynx constitute around 1% of all injuries. The great majority of the injuries of the larynx happens during playing. The effects of these injuries may appear insignificant however, not always the direct clinical symptoms correlate with the degree of respiratory tract failure. The symptoms of laryngeal injuries depend on the extension and strength of the trauma and always relate to impair patency of respiratory tract. The aim of the study is to compare two diagnostic methods: laryngoscopy and ultrasonography in evaluation of laryngeal injuries in children. MethodsIn the Department of Pediatric Otolaryngology, Medical University of Warsaw, in the period between 2004 and 2010 there were hospitalised 15 children with external injury of the larynx. ResultsFrom among 15 hospitalized children, 7 were qualified as not serious trauma and were treated preservatively and the other 8 as sever trauma. The mechanism of traumas was diverse. Dyspnea was a predominating symptom, the others included hoarsness, change in voice quality, even aphonia, pain while speaking and swallowing, cough and hemoptysis. ConclusionsDirect laryngoscopy is a standard in diagnostics of the injuries of the larynx. Ultrasonography of the larynx is recommended in every case of laryngeal injury as an additional non-invasive complementary diagnostic examination.

AB0168 Relationship between voice quality parameters and clinical manifestation of rheumatoid arthritis

BackgroundRheumatoid arthritis (RA) is a chronic, multisystem autoimmune disease manifested by joint inflammation and damage including also joints and laryngeal cartilages which play an essential role in the process of...

Perceptual consequences of changes in epilaryngeal area and shape

Decreasing epilaryngeal area has been shown to increase glottal flow pulse skewing and harmonic amplitudes [Titze, J. Acoust. Soc. Am. 123, 2733 (2008)]. It is not known, however, whether listeners perceive voice quality changes when epilaryngeal area is altered, or if perceived quality is different if the area change occurs at the ventricular folds or aryepiglottic (AE) folds. In this study, a kinematic vocal tract model was used to create five epilaryngeal cavity shapes resulting from constriction and retraction of the ventricular and AE folds. Four voice sources simulating varying degrees of vocal deviation were filtered through the five shapes for a total of 20 stimuli. Fourteen listeners completed a sort and rate task. Results were analyzed using multidimensional scaling (MDS). Altering the epilaryngeal cavity shape resulted in voice quality differences, and perceptual distances differed by voice source. AE fold constriction was perceived most differently from other shapes for all talkers. Ventricular fold constriction was perceived most similar to AE constriction for 3 of the 4 voice sources. Glottal flow and acoustic differences for each epilaryngeal shape will be described and related to the perceived differences in voice quality.

An overlooked complication of hemodialysis: Hoarseness

In hemodialysis patients, some degree of transient hoarseness may occur at the end of the dialysis, and it may be a wearisome, recurrent, and severe state for some hemodialysis patients. However, to date, it has not been a well-defined complication of hemodialysis. The aim of this study was to state this complication and to throw light on it. Four hundred fifty-nine hemodialysis patients were questioned about any change in voice quality during hemodialysis. The patients who had this complaint (n=70) were included in the study, and the group of patients who suffered hoarseness (subgroup 1: severe, subgroup 2: moderate, subgroup 3: mild) were compared with each other and with the control group, which did not suffer hoarseness (n=51). Hoarseness was found in 15.2% of the hemodialysis patients. The duration of their hoarseness was minimum 1 to maximum 24 hours. In the control group, coronary artery disease (P=0.056), congestive heart failure (P=0.049), autonomic neuropathy (P=0.001), severe intradialytic hypotensive attacks (P=0.000), heart valve abnormalities (P=0.000), and left ventricular diastolic dysfunction (P=0.000) were significantly lower than in hoarseness group. Older age (P=0.024), coronary artery disease (P=0.014), autonomic neuropathy (P=0.011), and intradialytic hypotensive attacks (P=0.0001), were associated with severe and moderate hoarseness. In the comparison of % change for systolic and diastolic blood pressure between the hoarseness subgroups, diastolic blood pressure change was not different (P=0.521), but systolic blood pressure change was statistically lower in mild group than moderate (P=0.033) and severe subgroup (P=0.029). Dialysis-induced hypotension may be the main contributor of transient hoarseness. Especially elderly and cardiovascularly compromised patients, who are vulnerable to rapid changes in volume status may experience it to serious extent and this complication may be mediated by autonomic nervous control related with volume depletion.

Acoustic and perceptual effects of changes in body layer stiffness in symmetric and asymmetric vocal fold models

At present, it is not well understood how changes in vocal fold biomechanics correspond to changes in voice quality. Understanding such cross-domain links from physiology to acoustics to perception in the "speech chain" is of both theoretical and clinical importance. This study investigates links between changes in body layer stiffness, which is regulated primarily by the thyroarytenoid muscle, and the consequent changes in acoustics and voice quality under left-right symmetric and asymmetric stiffness conditions. Voice samples were generated using three series of two-layer physical vocal fold models, which differed only in body stiffness. Differences in perceived voice quality in each series were then measured in a "sort and rate" listening experiment. The results showed that increasing body stiffness better maintained vocal fold adductory position, thereby exciting more high-order harmonics, differences that listeners readily perceived. Changes to the degree of left-right stiffness mismatch and the resulting left-right vibratory asymmetry did not produce perceptually significant differences in quality unless the stiffness mismatch was large enough to cause a change in vibratory mode. This suggests that a vibration pattern with left-right asymmetry does not necessarily result in a salient deviation in voice quality, and thus may not always be of clinical significance.