Effect of nodule size and stiffness on phonation threshold and collision pressures in a synthetic hemilaryngeal vocal fold model.

Synthetic vocal fold (VF) replicas were used to explore the role of nodule size and stiffness on kinematic, aerodynamic, and acoustic measures of voiced speech production. Emphasis was placed on determining how changes in collision pressure may contribute to the development of phonotrauma. This was performed by adding spherical beads with different sizes and moduli of elasticity at the middle of the medial surface of synthetic silicone VF models, representing nodules of varying size and stiffness. The VF models were incorporated into a hemilaryngeal flow facility. For each case, self-sustained oscillations were investigated at the phonation threshold pressure. It was found that increasing the nodule diameter increased the open quotient, phonation threshold pressure, and phonation threshold flow rate. However, these values did not change considerably as a function of the modulus of elasticity of the nodule. Nevertheless, the ratio of collision pressure to subglottal pressure increased significantly for both increasing nodule size and stiffness. This suggests that over time, both growth in size and fibrosis of nodules will lead to an increasing cycle of compensatory vocal hyperfunction that accelerates phonotrauma.

Bayesian estimation of vocal function measures using laryngeal high-speed videoendoscopy and glottal airflow estimates: An in vivo case study.

This study introduces the in vivo application of a Bayesian framework to estimate subglottal pressure, laryngeal muscle activation, and vocal fold contact pressure from calibrated transnasal high-speed videoendoscopy and oral airflow data. A subject-specific, lumped-element vocal fold model is estimated using an extended Kalman filter and two observation models involving glottal area and glottal airflow. Model-based inferences using data from a vocally healthy male individual are compared with empirical estimates of subglottal pressure and reference values for muscle activation and contact pressure in the literature, thus providing baseline error metrics for future clinical investigations.

Ambulatory monitoring of Lombard-related vocal characteristics in vocally healthy female speakers.

Speakers typically modify their voice in the presence of increased background noise levels, exhibiting the classic Lombard effect. Lombard-related characteristics during everyday activities were recorded from 17 vocally healthy women who wore an acoustic noise dosimeter and ambulatory voice monitor. The linear relationship between vocal sound pressure level and environmental noise level exhibited an average slope of 0.54 dB/dB and value of 72.8 dB SPL at 50 dBA when correlation coefficients were greater than 0.4. These results, coupled with analyses of spectral and cepstral vocal function measures, provide normative ambulatory Lombard characteristics for comparison with patients with voice-use related disorders.

Identifying a creak probability threshold for an irregular pitch period detection algorithm.

Irregular pitch periods (IPPs) are associated with grammatically, pragmatically, and clinically significant types of nonmodal phonation, but are challenging to identify. Automatic detection of IPPs is desirable because accurately hand-identifying IPPs is time-consuming and requires training. The authors evaluated an algorithm developed for creaky voice analysis to automatically identify IPPs in recordings of American English conversational speech. To determine a perceptually relevant threshold probability, frame-by-frame creak probabilities were compared to hand labels, yielding a threshold of approximately 0.02. These results indicate a generally good agreement between hand-labeled IPPs and automatic detection, calling for future work investigating effects of linguistic and prosodic context.

The difference between first and second harmonic amplitudes correlates between glottal airflow and neck-surface accelerometer signals during phonation.

Miniature high-bandwidth accelerometers on the anterior neck surface are used in laboratory and ambulatory settings to obtain vocal function measures. This study compared the widely applied L1-L2 measure (historically, H1-H2)-the difference between the log-magnitude of the first and second harmonics-computed from the glottal airflow waveform with L1-L2 derived from the raw neck-surface acceleration signal in 79 vocally healthy female speakers. Results showed a significant correlation (r = 0.72) between L1-L2 values estimated from both airflow and accelerometer signals, suggesting that raw accelerometer-based estimates of L1-L2 may be interpreted as reflecting glottal physiological parameters and voice quality attributes during phonation.

Automatic speech and singing classification in ambulatory recordings for normal and disordered voices.

Ambulatory voice monitoring is a promising tool for investigating phonotraumatic vocal hyperfunction (PVH), associated with the development of vocal fold lesions. Since many patients with PVH are professional vocalists, a classifier was developed to better understand phonatory mechanisms during speech and singing. Twenty singers with PVH and 20 matched healthy controls were monitored with a neck-surface accelerometer-based ambulatory voice monitor. An expert-labeled ground truth data set was used to train a logistic regression on 15 subject-pairs with fundamental frequency and autocorrelation peak amplitude as input features. Overall classification accuracy of 94.2% was achieved on the held-out test set.

Measuring vocal motor skill with a virtual voice-controlled slingshot.

Successful voice training (e.g., singing lessons) and vocal rehabilitation (e.g., therapy for a voice disorder) involve learning complex, vocal behaviors. However, there are no metrics describing how humans learn new vocal skills or predicting how long the improved behavior will persist post-therapy. To develop measures capable of describing and predicting vocal motor learning, a theory-based paradigm from limb motor control inspired the development of a virtual task where subjects throw projectiles at a target via modifications in vocal pitch and loudness. Ten subjects with healthy voices practiced this complex vocal task for five days. The many-to-one mapping between the execution variables pitch and loudness and resulting target error was evaluated using an analysis that quantified distributional properties of variability: Tolerance, noise, covariation costs (TNC costs). Lag-1 autocorrelation (AC1) and detrended-fluctuation-analysis scaling index (SCI) analyzed temporal aspects of variability. Vocal data replicated limb-based findings: TNC costs were positively correlated with error; AC1 and SCI were modulated in relation to the task's solution manifold. The data suggests that vocal and limb motor learning are similar in how the learner navigates the solution space. Future work calls for investigating the game's potential to improve voice disorder diagnosis and treatment.

Acoustic speech analysis of patients with decompensated heart failure: A pilot study.

This pilot study used acoustic speech analysis to monitor patients with heart failure (HF), which is characterized by increased intracardiac filling pressures and peripheral edema. HF-related edema in the vocal folds and lungs is hypothesized to affect phonation and speech respiration. Acoustic measures of vocal perturbation and speech breathing characteristics were computed from sustained vowels and speech passages recorded daily from ten patients with HF undergoing inpatient diuretic treatment. After treatment, patients displayed a higher proportion of automatically identified creaky voice, increased fundamental frequency, and decreased cepstral peak prominence variation, suggesting that speech biomarkers can be early indicators of HF.

Average Ambulatory Measures of Sound Pressure Level, Fundamental Frequency, and Vocal Dose Do Not Differ Between Adult Females With Phonotraumatic Lesions and Matched Control Subjects.

OBJECTIVES: Clinical management of phonotraumatic vocal fold lesions (nodules, polyps) is based largely on assumptions that abnormalities in habitual levels of sound pressure level (SPL), fundamental frequency (f0), and/or amount of voice use play a major role in lesion development and chronic persistence. This study used ambulatory voice monitoring to evaluate if significant differences in voice use exist between patients with phonotraumatic lesions and normal matched controls. METHODS: Subjects were 70 adult females: 35 with vocal fold nodules or polyps and 35 age-, sex-, and occupation-matched normal individuals. Weeklong summary statistics of voice use were computed from anterior neck surface acceleration recorded using a smartphone-based ambulatory voice monitor. RESULTS: Paired t tests and Kolmogorov-Smirnov tests resulted in no statistically significant differences between patients and matched controls regarding average measures of SPL, f0, vocal dose measures, and voicing/voice rest periods. Paired t tests comparing f0 variability between the groups resulted in statistically significant differences with moderate effect sizes. CONCLUSIONS: Individuals with phonotraumatic lesions did not exhibit differences in average ambulatory measures of vocal behavior when compared with matched controls. More refined characterizations of underlying phonatory mechanisms and other potentially contributing causes are warranted to better understand risk factors associated with phonotraumatic lesions.

Statistical properties of linear prediction analysis underlying the challenge of formant bandwidth estimation.

Formant bandwidth estimation is often observed to be more challenging than the estimation of formant center frequencies due to the presence of multiple glottal pulses within a period and short closed-phase durations. This study explores inherently different statistical properties between linear prediction (LP)-based estimates of formant frequencies and their corresponding bandwidths that may be explained in part by the statistical bounds on the variances of estimated LP coefficients. A theoretical analysis of the Cramér-Rao bounds on LP estimator variance indicates that the accuracy of bandwidth estimation is approximately twice as low as that of center frequency estimation. Monte Carlo simulations of all-pole vowels with stochastic and mixed-source excitation demonstrate that the distributions of estimated LP coefficients exhibit expectedly different variances for each coefficient. Transforming the LP coefficients to formant parameters results in variances of bandwidth estimates being typically larger than the variances of respective center frequency estimates, depending on vowel type and fundamental frequency. These results provide additional evidence underlying the challenge of formant bandwidth estimation due to inherent statistical properties of LP-based speech analysis.

Real-time estimation of aerodynamic features for ambulatory voice biofeedback.

The development of ambulatory voice monitoring devices has the potential to improve the diagnosis and treatment of voice disorders. In this proof-of-concept study, real-time biofeedback is incorporated into a smartphone-based platform that records and processes neck surface acceleration. The focus is on utilizing aerodynamic measures of vocal function as a basis for biofeedback. This is done using regressed Z-scores to compare recorded values to normative estimates based on sound pressure level and fundamental frequency. Initial results from the analysis of different voice qualities suggest that accelerometer-based estimates of aerodynamic parameters can be used for real-time ambulatory biofeedback.

Consistency of the Signature of Phonotraumatic Vocal Hyperfunction Across Different Ambulatory Voice Measures.

PURPOSE: Although different factors and voice measures have been associated with phonotraumatic vocal hyperfunction (PVH), it is unclear what percentage of individuals with PVH exhibit such differences during their daily lives. This study used a machine learning approach to quantify the consistency with which PVH manifests according to ambulatory voice measures. Analyses included acoustic parameters of phonation as well as temporal aspects of phonation and rest, with the goal of determining optimally consistent signatures of PVH. METHOD: Ambulatory neck-surface acceleration signals were recorded over 1 week from 116 female participants diagnosed with PVH and age-, sex-, and occupation-matched vocally healthy controls. The consistency of the manifestation of PVH was defined as the percentage of participants in each group that exhibited an atypical signature based on a target voice measure. Evaluation of each machine learning model used nested 10-fold cross-validation to improve the generalizability of findings. In Experiment 1, we trained separate logistic regression models based on the distributional characteristics of 14 voice measures and durations of voicing and resting segments. In Experiments 2 and 3, features of voicing and resting duration augmented the existing distributional characteristics to examine whether more consistent signatures would result. RESULTS: Experiment 1 showed that the difference in the magnitude of the first two harmonics (H1-H2) exhibited the most consistent signature (69.4% of participants with PVH and 20.4% of controls had an atypical H1-H2 signature), followed by spectral tilt over eight harmonics (73.6% participants with PVH and 32.1% of controls had an atypical spectral tilt signature) and estimated sound pressure level (SPL; 66.9% participants with PVH and 27.6% of controls had an atypical SPL signature). Additionally, 77.6% of participants with PVH had atypical resting duration, with 68.9% exhibiting atypical voicing duration. Experiments 2 and 3 showed that augmenting the best-performing voice measures with univariate features of voicing or resting durations yielded only incremental improvement in the classifier's performance. CONCLUSIONS: Females with PVH were more likely to use more abrupt vocal fold closure (lower H1-H2), phonate louder (higher SPL), and take shorter vocal rests. They were also less likely to use higher fundamental frequency during their daily activities. The difference in the voicing duration signature between participants with PVH and controls had a large effect size, providing strong empirical evidence regarding the role of voice use in the development of PVH.

Toward Generalizable Machine Learning Models in Speech, Language, and Hearing Sciences: Estimating Sample Size and Reducing Overfitting.

PURPOSE: Many studies using machine learning (ML) in speech, language, and hearing sciences rely upon cross-validations with single data splitting. This study's first purpose is to provide quantitative evidence that would incentivize researchers to instead use the more robust data splitting method of nested k-fold cross-validation. The second purpose is to present methods and MATLAB code to perform power analysis for ML-based analysis during the design of a study. METHOD: First, the significant impact of different cross-validations on ML outcomes was demonstrated using real-world clinical data. Then, Monte Carlo simulations were used to quantify the interactions among the employed cross-validation method, the discriminative power of features, the dimensionality of the feature space, the dimensionality of the model, and the sample size. Four different cross-validation methods (single holdout, 10-fold, train-validation-test, and nested 10-fold) were compared based on the statistical power and confidence of the resulting ML models. Distributions of the null and alternative hypotheses were used to determine the minimum required sample size for obtaining a statistically significant outcome (5% significance) with 80% power. Statistical confidence of the model was defined as the probability of correct features being selected for inclusion in the final model. RESULTS: ML models generated based on the single holdout method had very low statistical power and confidence, leading to overestimation of classification accuracy. Conversely, the nested 10-fold cross-validation method resulted in the highest statistical confidence and power while also providing an unbiased estimate of accuracy. The required sample size using the single holdout method could be 50% higher than what would be needed if nested k-fold cross-validation were used. Statistical confidence in the model based on nested k-fold cross-validation was as much as four times higher than the confidence obtained with the single holdout-based model. A computational model, MATLAB code, and lookup tables are provided to assist researchers with estimating the minimum sample size needed during study design. CONCLUSION: The adoption of nested k-fold cross-validation is critical for unbiased and robust ML studies in the speech, language, and hearing sciences. SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.25237045.

Acoustic-Aerodynamic Voice Outcome Ratios Identify Changes in Vocal Function Following Vocal Fold Medialization for Unilateral Vocal Fold Paralysis.

PURPOSE: This study aimed to determine whether ratio-based measures that combine acoustic (output) and aerodynamic (input) parameters detect postoperative change in vocal function following vocal fold medialization for unilateral vocal fold paralysis. METHOD: Pre- and postoperative acoustic and aerodynamic measures were analyzed retrospectively from 149 patients who underwent vocal fold medialization for unilateral vocal fold paralysis. A 2 × 2 repeated-measures analysis of variance was conducted for each of four acoustic-aerodynamic ratios-traditional vocal efficiency (VE), sound pressure level to aerodynamic power (SPL/AP), SPL to average airflow (SPL/AFLOW), and SPL to subglottal pressure (SPL/Ps)-to investigate the main effects and interaction of treatment stage and loudness level (comfortable and loud). RESULTS: The patient group showed significant postoperative improvements in self reports of vocal function (voice-related quality of life) and clinical auditory-perceptual judgments of dysphonia (consensus auditory-perceptual evaluation of voice). Main effects for both treatment stage and loudness level were statistically significant for all measures except SPL/Ps. There were interaction effects for VE and SPL/AP, suggesting that magnitude of the treatment effect differs based on loudness. SPL/AFLOW had medium-to-large effect sizes in both loudness conditions. There were postoperative changes in SPL/Ps that were dependent on the magnitude of the reduction in AFLOW; as expected, SPL/Ps increased postoperatively in a subgroup that had large postoperative reductions in AFLOW at the comfortable loudness level. CONCLUSIONS: Acoustic-aerodynamic ratios can aid in tracking changes in vocal function following vocal fold medialization. SPL/AFLOW exhibited the largest effect size, which is expected since a reduction in abnormally high AFLOW typically accompanies the increased modulation of glottal air flow associated with successful vocal fold medialization. Future study is needed to model physiological changes in acoustic-aerodynamic voice outcome ratios across different types of voice disorders.

Quantifying the Occupational Voice Use of Teachers.

Purpose: The teaching profession is a high-voice use occupation at elevated risk for developing voice disorders. Continued research on teachers' vocal demands is necessary to advocate for and establish vocal health programs. This study quantified ambulatory vocal dose measures for teachers during both on- and off-work periods, comparing their occupational voice use to that in other studies that have reported percent phonation ranging from 17% to 30%. Method: Participants included 26 full-time, female school teachers between 23 and 55 years of age across multiple grades and subjects, including individuals with and without a voice disorder. Ambulatory voice data were collected from weeklong voice monitoring that recorded phonatory activity through anterior neck-surface vibration. Three vocal dose measures-time, cycle, and distance doses-were computed for each participant for three time periods: on-work weekdays, off-work weekdays, and off-work weekend days. Results: The teachers' average percent phonation was 16.2% on-work weekdays, 8.4% off-work weekdays, and 8.0% off-work weekend days. No statistically significant differences for vocal dose measures were found between off-work weekdays and weekend days. Overall, all vocal dose measures were approximately 2 times higher during work relative to off-work time periods. Conclusions: This study provides values for vocal dose measures for school teachers using ambulatory voice-monitoring technology. The vocal demands of this particular teacher sample and voice activity detection algorithm are potential factors contributing to percent phonation values on the lower end of the range reported in the literature. Future work is needed to continue to understand occupational voice use and its associated risks related to voice health, with the ultimate goal of preventing and managing voice disorders in individuals engaged in high-risk occupations.

Acoustic Voice and Speech Biomarkers of Treatment Status during Hospitalization for Acute Decompensated Heart Failure.

This study investigates acoustic voice and speech features as biomarkers for acute decompensated heart failure (ADHF), a serious escalation of heart failure symptoms including breathlessness and fatigue. ADHF-related systemic fluid accumulation in the lungs and laryngeal tissues is hypothesized to affect phonation and respiration for speech. A set of daily spoken recordings from 52 patients undergoing inpatient ADHF treatment was analyzed to identify voice and speech biomarkers for ADHF and to examine the trajectory of biomarkers during treatment. Results indicated that speakers produce more stable phonation, a more creaky voice, faster speech rates, and longer phrases after ADHF treatment compared to their pre-treatment voices. This project builds on work to develop a method of monitoring ADHF using speech biomarkers and presents a more detailed understanding of relevant voice and speech features.

Detecting Mild Phonotrauma in Daily Life.

OBJECTIVE: The aim of this study was to gain quantitative insights into the role of daily voice use associated with mild phonotrauma via the Daily Phonotrauma Index (DPI), a measure derived from neck-surface acceleration magnitude (NSAM) and difference between the first two harmonic magnitudes (H1 - H2). METHODS: An ambulatory voice monitor recorded weeklong voice use for 151 female patients with phonotraumatic vocal hyperfunction (PVH) and 181 female vocally healthy controls. Three laryngologists rated phonotrauma severity from each patient's laryngoscopy. Mixed generalized linear models evaluated the accuracy, sensitivity, and specificity of the original DPI trained on all patients versus a mild DPI version trained on only patients rated with mild phonotrauma. Individual contribution of NSAM and H1 - H2 to each DPI model was also evaluated. RESULTS: Reliability across the laryngologists' phonotrauma ratings was moderate (Fleiss κ = 0.41). There were 70, 69, and 12 patients with mild, moderate, and severe phonotrauma, respectively. The mild DPI, compared to the original DPI, correctly classified more patients with mild phonotrauma (Cohen's d = 0.9) and less controls (d = -0.9) and did not change in overall accuracy. H1 - H2 contributed less to mild phonotrauma classification than NSAM for mild DPI. CONCLUSIONS: Compared with the original DPI, the mild DPI exhibited higher sensitivity to mild phonotrauma and lower specificity to controls, but the same overall classification accuracy. These results support the mild DPI as a promising detector of early phonotrauma and that NSAM may be associated with early phonotrauma, and H1 - H2 may be a biomarker associated with vocal fold vibration in the presence of lesions. LEVEL OF EVIDENCE: Level 4, case-control study Laryngoscope, 133:3094-3099, 2023.

High-speed videoendoscopic analysis of relationships between cepstral-based acoustic measures and voice production mechanisms in patients undergoing phonomicrosurgery.

OBJECTIVES: There is increased interest in using cepstral-based acoustic measures for objective clinical voice assessment because of their apparent advantages over more time-honored methods, but there is a paucity of information about how these newer measures relate to underlying phonatory mechanisms. METHODS: We investigated the relationships between the acoustic cepstral peak magnitude (CPM) and high-speed videoendoscopy (HSV)-based measures of vocal fold phonatory function in 20 subjects who underwent phonomicrosurgery for vocal fold lesions. Acoustic and imaging data were acquired during sustained vowel phonation before and after surgery. RESULTS: The changes in the measures between presurgical and postsurgical assessments showed that the CPM correlated significantly with an HSV-based measure combining fundamental frequency deviation and average speed quotient (r = 0.70; p < 0.001) in a multiple linear regression, and that the variation in the CPM could also be attributed to trading relationships between the HSV-based measures of vibratory phase asymmetry and glottal closure. CONCLUSIONS: These initial results demonstrate that the clinical utility of cepstral-based measures can be enhanced by a better understanding of how these acoustic measures relate to underlying phonatory mechanisms. The CPM seems to integrate information about aperiodicity in vocal fold vibration, the relative speed of glottal closure, and estimates of glottal noise generation.

Kalman-based autoregressive moving average modeling and inference for formant and antiformant tracking.

Vocal tract resonance characteristics in acoustic speech signals are classically tracked using frame-by-frame point estimates of formant frequencies followed by candidate selection and smoothing using dynamic programming methods that minimize ad hoc cost functions. The goal of the current work is to provide both point estimates and associated uncertainties of center frequencies and bandwidths in a statistically principled state-space framework. Extended Kalman (K) algorithms take advantage of a linearized mapping to infer formant and antiformant parameters from frame-based estimates of autoregressive moving average (ARMA) cepstral coefficients. Error analysis of KARMA, wavesurfer, and praat is accomplished in the all-pole case using a manually marked formant database and synthesized speech waveforms. KARMA formant tracks exhibit lower overall root-mean-square error relative to the two benchmark algorithms with the ability to modify parameters in a controlled manner to trade off bias and variance. Antiformant tracking performance of KARMA is illustrated using synthesized and spoken nasal phonemes. The simultaneous tracking of uncertainty levels enables practitioners to recognize time-varying confidence in parameters of interest and adjust algorithmic settings accordingly.

Framework for Indirect Spatial Calibration of the Horizontal Plane of Endoscopic Laryngeal Images.

OBJECTIVE: Calibrated horizontal-plane measurements from laryngeal images could contribute significantly to refining evidence-based practice and developing patient-specific models and precision-medicine approaches. Laser-projection endoscopes can address the need for direct calibrated measures; however, these systems are not widely available. This study presents the framework for an alternative indirect horizontal-plane calibration approach. METHOD: A spatial attribute of a common object, a distinct characteristic that is maintained across images, may be used as a scale for the normalization of other spatial measurements. The outcome of this indirect approach could be used for absolute measurements (eg, in units of mm) or relative measurements (eg, percent change), depending on the information that is available from the common attribute. The required conditions of a common attribute for achieving a valid calibration outcome were studied. Three conditions were derived: registration accuracy of the common attribute, size consistency of the common attribute, and similarity in the vertical distance between the region of interest (ROI) (eg, vocal fold) and the common attribute. Any common attribute satisfying these three conditions was called proper and would result in a valid indirect calibration outcome. Three tests were presented for evaluating the properness of a common attribute. A data-driven statistical method was presented that can evaluate the registration accuracy of a common attribute. The second test used variation in calibrated lengths of a common attribute under different phonatory configurations for evaluating the size consistency condition. Finally, the effect of differences between vertical distances of the ROI and the common attribute was mathematically tested and quantified. The application of the proposed framework for indirect calibration was demonstrated using a pre existing dataset with a vocal fold as the ROI and four different common attributes (vocal fold length, vocal fold width, blood vessel on the vocal fold, and blood vessel on nearby tissue). RESULTS: The proposed registration-accuracy test was able to detect and eliminate instances of common attributes with low accuracies. The analysis suggested that among the studied four common attributes, the vocal fold length had the highest (ie, best) registration accuracy; however, the vocal fold length exhibited the lowest (ie, worst) size consistency. The analysis also suggested that, among the studied attributes, the vocal fold width offered the best trade-off among the three conditions and, hence, was a proper common attribute for calibrating spatial aspects of the vocal folds (length, displacement of edges, velocity, etc). CONCLUSION: Indirect calibration is a feasible alternative for calibration of laryngeal endoscopic images, given a proper common attribute is selected. Future work is needed to systematically evaluate the effects of various phonatory conditions on the characteristics of common attributes.