Research Investigations (Peer-Reviewed)

2015
Y. - A. S. Lien, et al., “Voice relative fundamental frequency via neck-skin acceleration in individuals with voice disorders,” Journal of Speech, Language, and Hearing Research, vol. 58, no. 5, pp. 1482-1487, 2015. Publisher's VersionAbstract

Abstract Purpose: This study investigated the use of neck-skin acceleration for relative fundamental frequency (RFF) analysis. Method: Forty individuals with voice disorders associated with vocal hyperfunction and 20 age- and sex-matched control participants were recorded with a subglottal neck-surface accelerometer and a microphone while producing speech stimuli appropriate for RFF. Rater reliabilities, RFF means, and RFF standard deviations derived from the accelerometer were compared with those derived from the microphone. Results: RFF estimated from the accelerometer had slightly higher intrarater reliability and identical interrater reliability compared with values estimated with the microphone. Although sensor type and the Vocal Cycle × Sensor and Vocal Cycle × Sensor × Group interactions showed significant effects on RFF means, the typical RFF pattern could be derived from either sensor. For both sensors, the RFF of individuals with vocal hyperfunction was lower than that of the controls. Sensor type and its interactions did not have significant effects on RFF standard deviations. Conclusions: RFF can be reliably estimated using an accelerometer, but these values cannot be compared with those collected via microphone. Future studies are needed to determine the physiological basis of RFF and examine the effect of sensors on RFF in practical voice assessment and monitoring settings.

Paper
2014
M. Ghassemi, et al., “Learning to detect vocal hyperfunction from ambulatory neck-surface acceleration features: Initial results for vocal fold nodules,” IEEE Transactions on Biomedical Engineering, vol. 61, no. 6, pp. 1668-1675, 2014. Publisher's VersionAbstract

Voice disorders are medical conditions that often result from vocal abuse/misuse which is referred to generically as vocal hyperfunction. Standard voice assessment approaches cannot accurately determine the actual nature, prevalence, and pathological impact of hyperfunctional vocal behaviors because such behaviors can vary greatly across the course of an individual's typical day and may not be clearly demonstrated during a brief clinical encounter. Thus, it would be clinically valuable to develop noninvasive ambulatory measures that can reliably differentiate vocal hyperfunction from normal patterns of vocal behavior. As an initial step toward this goal we used an accelerometer taped to the neck surface to provide a continuous, noninvasive acceleration signal designed to capture some aspects of vocal behavior related to vocal cord nodules, a common manifestation of vocal hyperfunction. We gathered data from 12 female adult patients diagnosed with vocal fold nodules and 12 control speakers matched for age and occupation. We derived features from weeklong neck-surface acceleration recordings by using distributions of sound pressure level and fundamental frequency over 5-min windows of the acceleration signal and normalized these features so that intersubject comparisons were meaningful. We then used supervised machine learning to show that the two groups exhibit distinct vocal behaviors that can be detected using the acceleration signal. We were able to correctly classify 22 of the 24 subjects, suggesting that in the future measures of the acceleration signal could be used to detect patients with the types of aberrant vocal behaviors that are associated with hyperfunctional voice disorders.

Paper
2013
M. Zañartu, J. C. Ho, D. D. Mehta, R. E. Hillman, and G. R. Wodicka, “Subglottal impedance-based inverse filtering of voiced sounds using neck surface acceleration,” IEEE Transactions on Audio, Speech, and Language Processing, vol. 21, pp. 1929-1939, 2013.Abstract

A model-based inverse filtering scheme is proposed for an accurate, non-invasive estimation of the aerodynamic source of voiced sounds at the glottis. The approach, referred to as subglottal impedance-based inverse filtering (IBIF), takes as input the signal from a lightweight accelerometer placed on the skin over the extrathoracic trachea and yields estimates of glottal airflow and its time derivative, offering important advantages over traditional methods that deal with the supraglottal vocal tract. The proposed scheme is based on mechano-acoustic impedance representations from a physiologically-based transmission line model and a lumped skin surface representation. A subject-specific calibration protocol is used to account for individual adjustments of subglottal impedance parameters and mechanical properties of the skin. Preliminary results for sustained vowels with various voice qualities show that the subglottal IBIF scheme yields comparable estimates with respect to current aerodynamics-based methods of clinical vocal assessment. A mean absolute error of less than 10% was observed for two glottal airflow measures—maximum flow declination rate and amplitude of the modulation component—that have been associated with the pathophysiology of some common voice disorders caused by faulty and/or abusive patterns of vocal behavior (i.e., vocal hyperfunction). The proposed method further advances the ambulatory assessment of vocal function based on the neck acceleration signal, that previously have been limited to the estimation of phonation duration, loudness, and pitch. Subglottal IBIF is also suitable for other ambulatory applications in speech communication, in which further evaluation is underway.

Paper
2012
D. D. Mehta, S. M. Zeitels, J. A. Burns, A. D. Friedman, D. D. Deliyski, and R. E. Hillman, “High-speed videoendoscopic analysis of relationships between cepstral-based acoustic measures and voice production mechanisms in patients undergoing phonomicrosurgery,” Annals of Otology, Rhinology, and Laryngology, vol. 121, pp. 341-347, 2012. Paper
D. D. Mehta, D. Rudoy, and P. J. Wolfe, “Kalman-based autoregressive moving average modeling and inference for formant and antiformant tracking,” The Journal of the Acoustical Society of America, vol. 132, no. 3, pp. 1732-1746, 2012. Publisher's Version Paper code
D. D. Mehta, M. Zañartu, S. W. Feng, H. A. Cheyne II, and R. E. Hillman, “Mobile voice health monitoring using a wearable accelerometer sensor and a smartphone platform,” IEEE Transactions on Biomedical Engineering, vol. 59, no. 11, pp. 3090-3096, 2012. Publisher's VersionAbstract

Many common voice disorders are chronic or recurring conditions that are likely to result from faulty and/or abusive patterns of vocal behavior, referred to generically as vocal hyperfunction. An ongoing goal in clinical voice assessment is the development and use of noninvasively derived measures to quantify and track the daily status of vocal hyperfunction so that the diagnosis and treatment of such behaviorally based voice disorders can be improved. This paper reports on the development of a new, versatile, and cost-effective clinical tool for mobile voice monitoring that acquires the high-bandwidth signal from an accelerometer sensor placed on the neck skin above the collarbone. Using a smartphone as the data acquisition platform, the prototype device provides a user-friendly interface for voice use monitoring, daily sensor calibration, and periodic alert capabilities. Pilot data are reported from three vocally normal speakers and three subjects with voice disorders to demonstrate the potential of the device to yield standard measures of fundamental frequency and sound pressure level and model-based glottal airflow properties. The smartphone-based platform enables future clinical studies for the identification of the best set of measures for differentiating between normal and hyperfunctional patterns of voice use.

Paper
2011
S. S. Karajanagi, et al., “Assessment of canine vocal fold function after injection of a new biomaterial designed to treat phonatory mucosal scarring,” Annals of Otology, Rhinology, and Laryngology, vol. 120, no. 3, pp. 175-184, 2011. Publisher's Version Paper
D. D. Mehta, D. D. Deliyski, T. F. Quatieri, and R. E. Hillman, “Automated measurement of vocal fold vibratory asymmetry from high-speed videoendoscopy recordings,” Journal of Speech, Language, and Hearing Research, vol. 54, no. 1, pp. 47-54, 2011. Publisher's VersionAbstract

Purpose: In prior work, a manually derived measure of vocal fold vibratory phase asymmetry correlated to varying degrees with visual judgments made from laryngeal high-speed videoendoscopy (HSV) recordings. This investigation extended this work by establishing an automated HSV-based framework to quantify 3 categories of vocal fold vibratory asymmetry. Method: HSV-based analysis provided for cycle-to-cycle estimates of left-right phase asymmetry, left-right amplitude asymmetry, and axis shift during glottal closure for 52 speakers with no vocal pathology producing comfortable and pressed phonation. An initial cross-validation of the automated left-right phase asymmetry measure was performed by correlating the measure with other objective and subjective assessments of phase asymmetry. Results: Vocal fold vibratory asymmetry was exhibited to a similar extent in both comfortable and pressed phonations. The automated measure of left-right phase asymmetry strongly correlated with manually derived measures and moderately correlated with visual-perceptual ratings. Correlations with the visual-perceptual ratings remained relatively consistent as the automated measure was derived from kymograms taken at different glottal locations. Conclusions: An automated HSV-based framework for the quantification of vocal fold vibratory asymmetry was developed and initially validated. This framework serves as a platform for investigating relationships between vocal fold tissue motion and acoustic measures of voice function.

Paper
D. D. Mehta, M. Zañartu, T. F. Quatieri, D. D. Deliyski, and R. E. Hillman, “Investigating acoustic correlates of human vocal fold vibratory phase asymmetry through modeling and laryngeal high-speed videoendoscopy,” The Journal of the Acoustical Society of America, vol. 130, pp. 3999-4009, 2011.Abstract

Vocal fold vibratory asymmetry is often associated with inefficient sound production through its impact on source spectral tilt. This association is investigated in both a computational voice production model and a group of 47 human subjects. The model provides indirect control over the degree of left-right phase asymmetry within a nonlinear source-filter framework, and high-speed videoendoscopy provides in vivo measures of vocal fold vibratory asymmetry. Source spectral tilt measures are estimated from the inverse-filtered spectrum of the simulated and recorded radiated acoustic pressure. As expected, model simulations indicate that increasing left-right phase asymmetry induces steeper spectral tilt. Subject data, however, reveal that none of the vibratory asymmetry measures correlates with spectral tilt measures. Probing further into physiological correlates of spectral tilt that might be affected by asymmetry, the glottal area waveform is parameterized to obtain measures of the open phase (open/plateau quotient) and closing phase (speed/closing quotient). Subjects' left-right phase asymmetry exhibits low, but statistically significant, correlations with speed quotient (r=0.45) and closing quotient (r=-0.39). Results call for future studies into the effect of asymmetric vocal fold vibration on glottal airflow and the associated impact on voice source spectral properties and vocal efficiency.

Paper
M. Zañartu, D. D. Mehta, J. C. Ho, G. R. Wodicka, and R. E. Hillman, “Observation and analysis of in vivo vocal fold tissue instabilities produced by nonlinear source-filter coupling: A case study,” The Journal of the Acoustical Society of America, vol. 129, pp. 326-339, 2011. Paper
2010
D. D. Mehta, D. D. Deliyski, S. M. Zeitels, T. F. Quatieri, and R. E. Hillman, “Voice production mechanisms following phonosurgical treatment of early glottic cancer,” Annals of Otology, Rhinology, and Laryngology, vol. 119, pp. 1-9, 2010. Publisher's VersionAbstract

Objectives: Although near-normal conversational voices can be achieved with the phonosurgical management of earlyglottic cancer, there are still acoustic and aerodynamic deficits in vocal function that must be better understood to helpfurther optimize phonosurgical interventions. Stroboscopic assessment is inadequate for this purpose.Methods: A newly developed color high-speed videoendoscopy (HSV) system that included time-synchronized recordingsof the acoustic signal was used to perform a detailed examination of voice production mechanisms in 14 subjects.Digital image processing techniques were used to quantify glottal phonatory function and to delineate relationships betweenvocal fold vibratory properties and acoustic perturbation measures.Results: The results for multiple measurements of vibratory asymmetry showed that 31% to 62% of subjects displayedhigher-than-normal average values, whereas the mean values for glottal closure duration (open quotient) and periodicityof vibration fell within normal limits. The average HSV-based measures did not correlate significantly with the acousticperturbation measures, but moderate correlations were exhibited between the acoustic measures and the SDs of the HSVbasedparameters.Conclusions: The use of simultaneous, time-synchronized HSV and acoustic recordings can provide new insights intopostoperative voice production mechanisms that cannot be obtained with stroboscopic assessment.

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