Laryngeal High-speed Videoendoscopy Research Articles

Spatial Segmentation for Laryngeal High-Speed Videoendoscopy in Connected Speech

This study proposes a new computational framework for automated spatial segmentation of the vocal fold edges in high-speed videoendoscopy (HSV) data during connected speech. This spatio-temporal analytic representation of the vocal folds enables the HSV-based measurement of the glottal area waveform and other vibratory characteristics in the context of running speech. HSV data were obtained from a vocally normal adult during production of the "Rainbow Passage." An algorithm based on an active contour modeling approach was developed for the analysis of HSV data. The algorithm was applied on a series of HSV kymograms at different intersections of the vocal folds to detect the edges of the vibrating vocal folds across the frames. This edge detection method follows a set of deformation rules for the active contours to capture the edges of the vocal folds through an energy optimization procedure. The detected edges in the kymograms were then registered back to the HSV frames. Subsequently, the glottal area waveform was calculated based on the area of the glottis enclosed by the vocal fold edges in each frame. The developed algorithm successfully captured the edges of the vocal folds in the HSV kymograms. This method led to an automated measurement of the glottal area waveform from the HSV frames during vocalizations in connected speech. The proposed algorithm serves as an automated method for spatial segmentation of the vocal folds in HSV data in connected speech. This study is one of the initial steps toward developing HSV-based measures to study vocal fold vibratory characteristics and voice production mechanisms in norm and disorder in the context of connected speech.

Description of the Features and Vibratory Behaviors of the Nyquist Plot Analyzed From Laryngeal High-Speed Videoendoscopy Images

Facilitative playback-based subjective measures offer a more reliable evaluation of the vocal fold vibration than those derived from direct inspection of video playback. One of the measures is a Nyquist plot, which presents the analyzed cycle-to-cycle vibratory information in a graphical form. While the potential is evident, the information of the features of the Nyquist plot, which the evaluation is based on, is still incomplete. The current identified features and their vibratory behaviors may be inadequate to guarantee accurate interpretation of the findings. The present study aims to address this issue by examining the features of the Nyquist plot and their vibratory behaviors. A total of 56 young normophonic speakers, that is, 20 males and 36 females were recruited as the participants. Each of them underwent laryngeal high-speed videoendoscopy to record the images of the vocal fold vibration, which were then analyzed to generate the Nyquist plots. The features were identified by inspecting the properties of the plot points forming the Nyquist plots. For each identified feature, its vibratory behaviors were examined. The results revealed four features: rim contour depicting the longitudinal phase difference; left edge shape signifying the glottal configuration, phase closure, and closed phase duration; rim width and rim pattern visualizing the regularity of glottal areas and the regularity of the intracycle variations, respectively. The findings present a more complete reference of the features and their vibratory behaviors that is pertinent for the Nyquist plot interpretation.

Effects of Using Laryngeal High-Speed Videoendoscopy Images Visualizing Partial Views of The Glottis on Measurement Outcomes

Ideally, an analysis method for laryngeal high-speed videoendoscopy (LHSV) based on the glottal area waveforms (GAW) requires images of a complete view of the glottis to ensure findings that are representatives of the vibratory behaviors of the whole vocal folds. However, in practice, the preferred images may not be obtained at all times. Often, the only available images that a clinician has to work with consist of a partial view of the glottis. This study aims to examine the effects of using images of a partial view of the glottis (ie, posterior-middle, anterior-middle, or middle) on the LHSV-based measures (ie, fundamental frequency (F0GAW), frequency perturbation (jitterGAW), amplitude perturbation (shimmerGAW), open quotient (OQGAW), and Nyquist plot). The participants consisted of 9 young normophonic females. The procedures involved LHSV recording of the vibration of the vocal folds. The images of the complete view of the glottis were analyzed to obtain the LHSV-based measures. The same images were used to simulate the images of partial views of the glottis by changing the outline of the region of interest to include only either the posterior-middle, anterior-middle, or middle parts of the glottis. The LHSV-based measures from the images of the partial views were then compared to those with the complete view . The results showed that all LHSV-based measures from the images of the posterior-middle view were similar to those of the complete view. However, only the F0GAW, jitterGAW, and shimmerGAW from the images of the anterior-middle and middle views were similar to those of the complete view. Lower OQGAW and different Nyquist plots than those of the complete view were generated by the images of the anterior-middle and middle views. In conclusion, all LHSV-based measures from the images of the posterior-middle view of the glottis, and only the F0GAW, jitterGAW, and shimmerGAW from the images of the anterior-middle and middle views of the glottis reflect the vibratory behaviors of the whole vocal folds. The same conclusion could not be applied to the OQGAW and Nyquist plots of the images of the anterior-middle and middle views of the glottis. A possible effect of the presence or absence of a posterior glottal gap on the findings warrants further confirmation.

Analysis Method for Laryngeal High-Speed Videoendoscopy: Development of the Criteria for the Measurement Input

Despite its clear advantages, laryngeal high-speed videoendoscopy (LHSV) has not yet been accepted as a routine imaging tool for the evaluation of vocal fold vibration due to the unavailability of methods to effectively analyze the huge number of images from the LHSV recording. Recently, a promising LHSV-based analysis method has been introduced. The ability of this analysis method in studying the vocal fold vibratory behaviors had been substantially demonstrated. However, some practical aspects of its clinical applications still require further attention. Most fundamental is that the criteria for the measurement input ie, a segment of interest (SOI), which has not been fully defined. Particularly, the length of the SOI and the location along the sample, where it needs to be selected require further confirmation. Meanwhile, the analysis using any options of a well-delineated glottal area demands verification. Without clear criteria for the SOI, it is difficult to demonstrate the relevance of this analysis method in clinical voice assessment. Therefore, the aim of the present study is to establish the criteria for the SOI, which involved the investigations on the length of the SOI and the location along the sample, where it needs to be selected, as well as the use of any options of a well-delineated glottal area for analysis. The participants in the present study consisted of 36 young normophonic females. The methods involved LHSV recording of the images of the vibrating vocal folds. The captured images were then analyzed using the method. The LHSV-based measures from the analyses were compared according to the specified procedures of each investigation. Results indicated that 2000 frames should be used as the SOI length. The SOI could be selected at any location along the sample as long as well-delineated glottal areas were observed. With the current findings, a more conclusive measurement protocol is available to ensure reliable LHSV-based measures. The findings further support this analysis method for clinical application, which in turn promote LHSV as a reliable laryngeal imaging tool in clinical setting.

Accurate detection of spatially calibrating laser points during transnasal, fiberoptic, laryngeal high-speed videoendoscopy using support vector machine

Performing calibrated spatial measurements of vocal fold structures (including pathology) and kinematics during phonation is essential for developing patient-specific voice production models and better quantifying treatment outcomes. Unfortunately, conventional videoendoscopic images cannot provide such measurements. However, adding laser-based fiducial markers to the field of view (FOV) can provide measurements in the coronal and transverse planes. Accurate detection of the laser points during in vivo recordings is a pre-requisite of such a measurement. This study presents a novel method based on machine learning for detection of the laser points. A custom-developed transnasal, fiberoptic endoscope projected a pattern of 7 × 7 green laser points on the FOV during sustained vowel tokens, which was recorded with a color high-speed video camera at 6000 frames per second. Analysis of the images showed that each laser point travels along a unique and deterministic trajectory. Based on this, the classification score of a support vector machine was employed for maximizing the posterior probability and finding the most probable laser point in each trajectory. Classification features were tailored to account for geometrical shape and gradient profile of laser points. Additionally, features were extracted from red, green, and blue color channels for accurate distinction between laser points and reflection light.

Influence of spatial camera resolution in high-speed videoendoscopy on laryngeal parameters.

In laryngeal high-speed videoendoscopy (HSV) the area between the vibrating vocal folds during phonation is of interest, being referred to as glottal area waveform (GAW). Varying camera resolution may influence parameters computed on the GAW and hence hinder the comparability between examinations. This study investigates the influence of spatial camera resolution on quantitative vocal fold vibratory function parameters obtained from the GAW. In total 40 HSV recordings during sustained phonation (20 healthy males and 20 healthy females) were investigated. A clinically used Photron Fastcam MC2 camera with a frame rate of 4000 fps and a spatial resolution of 512×256 pixels was applied. This initial resolution was reduced by pixel averaging to (1) a resolution of 256×128 and (2) to a resolution of 128×64 pixels, yielding three sets of recordings. The GAW was extracted and in total 50 vocal fold vibratory parameters representing different features of the GAW were computed. Statistical analyses using SPSS Statistics, version 21, was performed. 15 Parameters showing strong mathematical dependencies with other parameters were excluded from the main analysis but are given in the Supporting Information. Data analysis revealed clear influence of spatial resolution on GAW parameters. Fundamental period measures and period perturbation measures were the least affected. Amplitude perturbation measures and mechanical measures were most strongly influenced. Most glottal dynamic characteristics and symmetry measures deviated significantly. Most energy perturbation measures changed significantly in males but were mostly unaffected in females. In females 18 of 35 remaining parameters (51%) and in males 22 parameters (63%) changed significantly between spatial resolutions. This work represents the first step in studying the impact of video resolution on quantitative HSV parameters. Clear influences of spatial camera resolution on computed parameters were found. The study results suggest avoiding the use of the most strongly affected parameters. Further, the use of cameras with high resolution is recommended to analyze GAW measures in HSV data.

Influence of Analyzed Sequence Length on Parameters in Laryngeal High-Speed Videoendoscopy

Laryngeal high-speed videoendoscopy (HSV) allows objective quantification of vocal fold vibratory characteristics. However, it is unknown how the analyzed sequence length affects some of the computed parameters. To examine if varying sequence lengths influence parameter calculation, 20 HSV recordings of healthy females during sustained phonation were investigated. The clinical prevalent Photron Fastcam MC2 camera with a frame rate of 4000 fps and a spatial resolution of 512 × 256 pixels was used to collect HSV data. The glottal area waveform (GAW), describing the increase and decrease of the area between the vocal folds during phonation, was extracted. Based on the GAW, 16 perturbation parameters were computed for sequences of 5, 10, 20, 50 and 100 consecutive cycles. Statistical analysis was performed using SPSS Statistics, version 21. Only three parameters (18.8%) were statistically significantly influenced by changing sequence lengths. Of these parameters, one changed until 10 cycles were reached, one until 20 cycles were reached and one, namely Amplitude Variability Index (AVI), changed between almost all groups of different sequence lengths. Moreover, visually observable, but not statistically significant, changes within parameters were observed. These changes were often most prominent between shorter sequence lengths. Hence, we suggest using a minimum sequence length of at least 20 cycles and discarding the parameter AVI.

Studying vocal fold non-stationary behavior during connected speech using high-speed videoendoscopy

Studying voice production during running speech can provide new knowledge about the mechanisms of voice production with and without disorder. Laryngeal high-speed videoendoscopy (HSV) systems are powerful tools for studying laryngeal function and, if coupled with flexible fiberoptic endoscopes, they can provide unique possibilities to measure vocal fold vibration with high temporal resolution during connected speech. Hence, we can measure the non-stationary behaviors of the vocal folds, such as the glottal attack and offset times in running speech. In this study, a custom-built flexible fiberoptic HSV system was used to record a “Rainbow Passage” production from a vocally normal female. Automated temporal and spatial segmentation algorithms were developed to determine the time stamps of the vibrating vocal folds and the edges of the vocal folds during phonation. The glottal attack time and offset times were then measured from the temporally and spatially segmented HSV images. The amplification ratio was computed during the phonation onset and the damping ratio was calculated at the offset of sustained portion of phonation. These measures can be used to describe the laryngeal mechanisms of voice production in connected speech.

Dependencies and Ill-designed Parameters Within High-speed Videoendoscopy and Acoustic Signal Analysis

The phonatory process is often judged during sustained phonation by analyzing the acoustic voice signal and the vocal fold vibrations. Many formulas and parameters have been suggested for qualifying the characteristics of the acoustic signal and the vocal fold vibrations during sustained phonation. These parameters are directly computed from the acoustic signal and the endoscopic glottal area waveform (GAW). The GAW is calculated from laryngeal high-speed videoendoscopy (HSV) recordings and describes the increase and decrease of the glottal area during the phonation process, that is, the opening and closing of the two oscillating vocal folds over time. However, some of the parameters have strong mathematical dependencies with one another and some are ill-defined. The purpose of this study is to identify mathematical dependencies between parameters with the aim of reducing their numbers and suggesting which parameters may best describe the properties of the GAW and the acoustical signal. In this preliminary investigation, 20 frequently used parameters are examined: 10 GAW only and 10 both GAW and acoustic parameters. In total 13 parameters can be neglected because of mathematical dependencies. In addition, nine of these parameters show problematic features that range from unexpected behavior to ill definition. Reducing the number of parameters appears to be necessary to standardize vocal fold function analysis. This may lead to better comparability of research results from different studies.

Temporal Segmentation for Laryngeal High-Speed Videoendoscopy in Connected Speech

This study proposes a gradient-based method for temporal segmentation of laryngeal high-speed videoendoscopy (HSV) data obtained during connected speech. A custom-developed HSV system coupled with a flexible fiberoptic nasolaryngoscope was used to record one vocally normal female participant during reading of the "Rainbow Passage." A gradient-based algorithm was developed to generate a motion window. When applied to the HSV data, the motion window acted as a filter tracking the location of the vibrating vocal folds. The glottal area waveform was estimated using a statistical-based image-processing approach. The vocal fold vibratory frequency was computed by an autocorrelation-based extraction of the fundamental frequency (f0) from the glottal area waveform. Temporal segmentation was then performed based on the f0 contour and automatic detection of the epiglottic obstructions. Additionally, visual temporal segmentation was performed by viewing the HSV images frame by frame to determine the time points of the vocalization onsets and offsets, and the epiglottic obstructions of the glottis. The time points resulting from the automatic and visual temporal segmentation methods were cross-validated. The f0-contour patterns of rise and fall resulting from the automatic algorithm were found to be in agreement with the visual inspection of the vibratory frequency change in the HSV data. This study demonstrated the feasibility of automatic temporal segmentation of HSV imaging of connected speech, which allows for mapping the video content into onsets, offsets, and epiglottic obstructions for each vocalization. Automated analysis of HSV imaging of connected speech has significant clinical potential for advancing instrumental voice assessment protocols.

Utility of Laryngeal High-speed Videoendoscopy in Clinical Voice Assessment

This study aimed to assess the utility of laryngeal high-speed videoendoscopy (HSV) as a clinical tool. This is a prospective study of 151 patients. A total of 151 adult patients (52 male, 99 female) underwent both videoendoscopy with stroboscopy (videostroboscopy) and HSV examination as part of a routine clinical voice assessment. At the time of the examination, ratings for videostroboscopy were reported in the clinical report. Next, the clinicians reviewed the HSV examination and indicated the changes in ratings of HSV relative to videostroboscopy. Finally, the clinical reports were reviewed by a clinician not involved in data collection or clinical care of the patients and noted differences between videostroboscopy and HSV clinical ratings, and resulting diagnoses were identified and grouped. Ratings of all vibratory features showed change between videostroboscopy and HSV. Mucosal wave and amplitude of vibration showed the largest percentage change, respectively, in 74% and 53% of the reports. They were followed by the features of glottal closure (36%), phase closure (32%), glottal edge (25%), and phase symmetry (21%). Ratings of supraglottic compression and vocal fold vertical level showed the least change between videostroboscopy and HSV. Changes in initial diagnosis owing to the inclusion of HSV were indicated in 7% of the cases. HSV may be an important laryngeal imaging technique for functional assessment of the pathophysiology of certain voice disorders. HSV could enable important refinements in the diagnosis and management of vocal fold pathology.

Phasegram Analysis of Vocal Fold Vibration Documented With Laryngeal High-speed Video Endoscopy

In a recent publication, the phasegram, a bifurcation diagram over time, has been introduced as an intuitive visualization tool for assessing the vibratory states of oscillating systems. Here, this nonlinear dynamics approach is augmented with quantitative analysis parameters, and it is applied to clinical laryngeal high-speed video (HSV) endoscopic recordings of healthy and pathological phonations. HSV data from a total of 73 females diagnosed as healthy (n = 42), or with functional dysphonia (n = 15) or with unilateral vocal fold paralysis (n = 16), were quantitatively analyzed. Glottal area waveforms (GAW) and left and right hemi-GAWs (hGAW) were extracted from the HSV recordings. Based on Poincaré sections through phase space-embedded signals, two novel quantitative parameters were computed: the phasegram entropy (PE) and the phasegram complexity estimate (PCE), inspired by signal entropy and correlation dimension computation, respectively. Both PE and PCE assumed higher average values (suggesting more irregular vibrations) for the pathological as compared with the healthy participants, thus significantly discriminating healthy group from the paralysis group (P = 0.02 for both PE and PCE). Comparisons of individual PE or PCE data for the left and the right hGAW within each subject resulted in asymmetry measures for the regularity of vocal fold vibration. The PCE-based asymmetry measure revealed significant differences between the healthy group and the paralysis group (P = 0.03). Quantitative phasegram analysis of GAW and hGAW data is a promising tool for the automated processing of HSV data in research and in clinical practice.

Laryngeal High-Speed Videoendoscopy: Sensitivity of Objective Parameters towards Recording Frame Rate.

The current use of laryngeal high-speed videoendoscopy in clinic settings involves subjective visual assessment of vocal fold vibratory characteristics. However, objective quantification of vocal fold vibrations for evidence-based diagnosis and therapy is desired, and objective parameters assessing laryngeal dynamics have therefore been suggested. This study investigated the sensitivity of the objective parameters and their dependence on recording frame rate. A total of 300 endoscopic high-speed videos with recording frame rates between 1000 and 15 000 fps were analyzed for a vocally healthy female subject during sustained phonation. Twenty parameters, representing laryngeal dynamics, were computed. Four different parameter characteristics were found: parameters showing no change with increasing frame rate; parameters changing up to a certain frame rate, but then remaining constant; parameters remaining constant within a particular range of recording frame rates; and parameters changing with nearly every frame rate. The results suggest that (1) parameter values are influenced by recording frame rates and different parameters have varying sensitivities to recording frame rate; (2) normative values should be determined based on recording frame rates; and (3) the typically used recording frame rate of 4000 fps seems to be too low to distinguish accurately certain characteristics of the human phonation process in detail.

On transition between voice registers: Data from high-speed laryngeal videoendoscopy

How specific aspects of vocal fold vibration alter voice register has long been a subject of interest. Transitions between vocal registers are often studied using dynamic vocal fold models and electroglottographic signals. Although laryngeal high-speed videoendoscopy has also been applied to study steady-state voice registers, there has been little such investigation on the transitions between registers. In this study, we examined voice register transitions using phonations in which vocal qualities varied continuously in fundamental frequency (F0), loudness, or voice quality (from breathy to pressed). Glottal area measures {open quotient and alternating-current to open quotient ratios [Chen et al., JASA 133, 1656–1666 (2013)]} and acoustic measures (F0, energy, and H1-H2) were studied using simultaneously collected laryngeal high-speed videoendoscopy and audio recordings from 15 subjects. The video recordings were collected transorally at 10 000 frames per second. Glottal area waveforms were extracted using GlotAnTools (Version 5) [Erlangen, Germany], and acoustic measures were gathered using VoiceSauce software and analysis-by-synthesis. Glottal area measures were compared to acoustic measures and their relationships to voice register transitions were explored.

The glottaltopogram: A method of analyzing high-speed images of the vocal folds

Laryngeal high-speed videoendoscopy is a state-of-the-art technique to examine physiological vibrational patterns of the vocal folds. With sampling rates of thousands of frames per second, high-speed videoendoscopy produces a large amount of data that is difficult to analyze subjectively. In order to visualize high-speed video in a straightforward and intuitive way, many methods have been proposed to condense the three-dimensional data into a few static images that preserve characteristics of the underlying vocal fold vibratory patterns. In this paper, we propose the “glottaltopogram,” which is based on principal component analysis of changes over time in the brightness of each pixel in consecutive video images. This method reveals the overall synchronization of the vibrational patterns of the vocal folds over the entire laryngeal area. Experimental results showed that this method is effective in visualizing pathological and normal vocal fold vibratory patterns.

The Evolution of Methods for Imaging Vocal Fold Phonatory Function

In this article, we provide a brief summary of the major technological advances that led to current methods for imaging vocal fold vibration during phonation including the development of indirect laryngoscopy, imaging of rapid motion, fiber optics, and digital image capture. We also provide a brief overview of new emerging technologies that could be used in the future for voice research and clinical voice assessment, including advances in laryngeal high-speed videoendoscopy, depth-kymography, and dynamic optical coherence tomography.

SIG 5 Perspectives Vol. 22, No. 1, July 2012

You have accessPerspectives on Speech Science and Orofacial DisordersCE Questions1 Jul 2012SIG 5 Perspectives Vol. 22, No. 1, July 2012Earn 0.05 CEUs on This Issue Daryush D. Mehta, and Robert E. Hillman Daryush D. Mehta Google Scholar More articles by this author and Robert E. Hillman Google Scholar More articles by this author https://doi.org/10.1044/ssod22.1.1-ce SectionsAboutPDF ToolsAdd to favoritesDownload CitationTrack Citations ShareFacebookTwitterLinked In The Evolution of Methods for Imaging Vocal Fold Phonatory Function by Daryush D. Mehta and Robert E. Hillman 1. Early researchers who attempted to produce stroboscopic images of vocal fold behavior had difficulty because: a clear image of the larynx was not possible the patient did not tolerate the procedure well there was a lack of adequately trained personnel to perform the procedure they had to determine the correct relationship between the vocal fundamental frequency and the flash rate of the strobe light being used 2. Fiber optic technology: allowed clinicians to examine individuals that previously could not tolerate imaging procedures allowed clinicians to capture slow motion images of vocal fold behavior was the first major advance in laryngeal imaging was first used in laryngeal imaging in the 1930s 3. Videokymography: allows the user to view the entire larynx at high-speed frame rates requires the clinician to pass a light through a perforated pinwheel samples a very small section of the video image at an exceptionally high frame rate is cumbersome because it requires large reels of cinematic film 4. A significant problem associated with modern laryngeal high-speed videoendoscopy is: that it is difficult to develop adequate data processing techniques the elevated risk to the patient finding appropriate research subjects getting adequate light to the larynx 5. Dynamic optical coherence tomography: is an alternative to endoscopy that provides excellent surface visualization of the mucosa allows imaging of tissue beneath the surface of the vocal fold is a common laryngeal imaging technique used in most voice clinics provides similar information to videokymography Additional Resources FiguresReferencesRelatedDetails Volume 22Issue 1July 2012Pages: C1-C1 History Published in issue: Jul 1, 2012 Get Permissions Add to your Mendeley library Metrics Topicsasha-topicsasha-sigsasha-article-typesleader-topicsCopyright & Permissions© 2012 American Speech-Language-Hearing AssociationPDF downloadLoading ...

Investigating acoustic correlates of human vocal fold vibratory phase asymmetry through modeling and laryngeal high-speed videoendoscopy.

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.

Use of laryngeal high-speed videoendoscopy systems to study voice production mechanisms in human subjects

Advances in laryngeal high-speed videoendoscopy (HSV) are making it possible to investigate critical relationships between vocal fold physiology and acoustic voice production in human subjects. Our group has developed HSV systems for clinical research with synchronous acquisition of acoustics, electroglottography, neck skin acceleration, and, in the most comprehensive setup, airflow and intraoral pressure. Key results will be presented from examinations of source-filter coupling and studies of the acoustic impact of vocal fold vibratory asymmetry in subjects with and without voice disorders. Findings hold potential clinical significance by revealing acoustic-HSV relationships not observable using standard stroboscopic imaging, as well as contributing to the direct evaluation and eventual improvement of voice production models. The work of T. F. Quatieri was supported by the Department of Defense under Air Force contract FA8721-05-C-0002. The work of other authors was supported by grants from the NIH National Institute on Deafness and Other Communication Disorders (T32 DC00038 and R01 DC007640) and by the Institute of Laryngology and Voice Restoration.

Observation and analysis of in vivo vocal fold tissue instabilities produced by nonlinear source-filter coupling: A case study

Different source-related factors can lead to vocal fold instabilities and bifurcations referred to as voice breaks. Nonlinear coupling in phonation suggests that changes in acoustic loading can also be responsible for this unstable behavior. However, no in vivo visualization of tissue motion during these acoustically induced instabilities has been reported. Simultaneous recordings of laryngeal high-speed videoendoscopy, acoustics, aerodynamics, electroglottography, and neck skin acceleration are obtained from a participant consistently exhibiting voice breaks during pitch glide maneuvers. Results suggest that acoustically induced and source-induced instabilities can be distinguished at the tissue level. Differences in vibratory patterns are described through kymography and phonovibrography; measures of glottal area, open/speed quotient, and amplitude/phase asymmetry; and empirical orthogonal function decomposition. Acoustically induced tissue instabilities appear abruptly and exhibit irregular vocal fold motion after the bifurcation point, whereas source-induced ones show a smoother transition. These observations are also reflected in the acoustic and acceleration signals. Added aperiodicity is observed after the acoustically induced break, and harmonic changes appear prior to the bifurcation for the source-induced break. Both types of breaks appear to be subcritical bifurcations due to the presence of hysteresis and amplitude changes after the frequency jumps. These results are consistent with previous studies and the nonlinear source-filter coupling theory.