Joerg Lohscheller

Variability of normal vocal fold dynamics for different vocal loading in one healthy subject investigated by phonovibrograms.

We investigate the potential of high-speed digital imaging technique (HSI) and the phonovibrogram (PVG) analysis in normal vocal fold dynamics by studying the effects of continuous voice use (vocal loading) during the workday. One healthy subject was recorded at sustained phonation 13 times within 2 consecutive days in the morning before and in the afternoon after vocal loading, respectively. Vocal fold dynamics were extracted and visualized by PVGs. The characteristic PVG patterns were extracted representing vocal fold vibration types. The parameter values were then analyzed by statistics regarding vocal load, left-right PVG asymmetries, anterior-posterior PVG asymmetries, and opening-closing differences. For the first time, the direct impact of vocal load could be determined by analyzing vocal fold dynamics. For same vocal loading conditions, equal dynamical behavior of the vocal folds were confirmed. Comparison of recordings performed in the morning with the recordings after work revealed significant changes in vibration behavior, indicating impact of occurring vocal load. Left-right asymmetries in vocal fold dynamics were found confirming earlier assumptions. Different dynamics between opening and closing procedure as well as for anterior and posterior parts were found. Constant voice usage stresses the vocal folds even in healthy subjects and can be detected by applying the PVG technique. Furthermore, left-right PVG asymmetries do occur in healthy voice to a certain extent. HSI in combination with PVG analysis seems to be a promising tool for investigation of vocal fold fatigue and pathologies resulting in small forms of dynamical changes.

Assessment of the variability of vocal fold dynamics within and between recordings with high-speed imaging and by phonovibrogram†‡§

The goal of the study was to assess the variability of healthy vocal fold dynamics. Quantitative parameters describing mean regularity and vibration characteristics of vocal fold dynamics along the entire glottal axis were analyzed.

Correlation between Psychometric Tests and Mismatch Negativity in Preschool Children

The objective was to determine whether mismatch negativity (MMN) is suitable to supplement subjective psychometric subtests of central hearing. We assessed 13 healthy children and 32 children with central auditory processing disorder (CAPD). Three different types of sound deviants were presented in a multi-deviant MMN design. At group level, the incidence of MMN was always higher in clinically diagnosed controls. Children with better results in the subtest Auditory Memory Span had a higher incidence of MMN. The controls also had peak latencies that occurred significantly earlier in frontal, central and temporal electrode sites. The area under the curve (AUC) displayed an asymmetric distribution in CAPD children, who tended to have a left-hemispheric dominance. AUC, peak latency, and the incidence of MMN reflected the discriminative ability of CAPD children. Hence, these characteristics could be used for investigating children with deficits in central hearing and can supplement psychometric tests.

A New Method to Analyze Distortion Product Otoacoustic Emissions (DPOAEs) in the High-Frequency Range Up to 18 kHz Using Windowed Periodograms

Distortion product otoacoustic emissions (DPOAEs) are widely used as an objective examination procedure to determine cochlear function. In a clinical routine setting, the amplitude of the DPOAE signal at 2f1-f2 is applied as an indicator for a potential hearing loss up to 8 kHz. Due to their poor signal-to-noise ratio, meatal nodes from standing waves and calibration issues, high-frequency DPOAEs >; 8 kHz have hardly been addressed in experimental and clinical audiology so far. Here, we present a new method of measuring DPOAE signal levels based on optimal maximum likelihood estimation with windowed power spectral density estimation of stochastic signals and filtering theory. Analysis of simulated data showed that the proposed method effectively reduces the disturbing noise floor compared to conventional averaging techniques. Robust DPOAE signals were measured in 20 ears from ten normally hearing young adults (21-27 years) from 0.5 to 18 kHz . Repeated DPOAE recordings in one individual yielded a good to very good test-retest reliability of the proposed method. These observations are discussed in the context of DPOAE signal processing and possible clinical applications of high-frequency DPOAE measurements.

Model‐based quantification of pathological voice production

Hoarseness, the primary symptom of voice disorders, results from irregular vocal fold vibrations. The oncological therapy of laryngeal cancer may even result in a total loss of voice if an excision of the larynx, and thus, the vocal folds, is necessary. State‐of‐the‐art voice rehabilitation technique in this case is the utilization of scarred tissue in the upper part of the esophagus for substitute voice production. The quality of laryngeal voice, as well as the substitute voice, primarily depends on the anatomy and the vibration patterns of the voice‐producing element. Using endoscopic high‐speed recordings, the voice generators are observed during voice production. In this work, a model‐based approach feasible for the analysis and objective quantification of vocal fold vibrations, as well as the PE dynamics, is presented. By means of an automatic parameter optimization, the dynamic of a biomechanical model of the considered voice‐producing element is fitted to the recorded vibration patterns. Thereby sp...

Electromotive Triggering and Single Sweep Analysis of Vestibular Evoked Myogenic Potentials (VEMPs)

Cervical (c) and ocular (o) vestibular evoked myogenic potentials (VEMPs) provide important tools for measuring otolith function. However, two major drawbacks of this method are encountered in clinical practice. First, recording of oVEMPs is compromised by small n10 amplitudes. Second, VEMP analysis is currently based on the averaging technique, resulting in a loss of information compared to single sweep analysis. Here, we: 1) developed a novel electromotive trigger mechanism for evoking VEMPs by bone-conducted vibration to the forehead and 2) established maximum entropy extraction of complex wavelet transforms for calculation of phase synchronization between VEMP single sweeps. Both c- and oVEMPs were recorded for n=10 healthy individuals. The oVEMP n10 amplitude was consistently higher (right: 24.84±9.71 μV; left: 27.40±14.55 μV) than previously described. Stable VEMP signals were reached after a smaller number of head taps (oVEMPs 6; cVEMPs 11) compared to current recommendations. Phase synchronization vectors and phase shift values were successfully determined for simulated and clinically recorded VEMPs, providing information about the impact of noise and phase jitter on the VEMP signal. Thus, the proposed method constitutes an easy-to-use approach for the fast detection and analysis of VEMPs in clinical practice.

Quantifying spatiotemporal properties of vocal fold dynamics based on a multiscale analysis of phonovibrograms.

In order to objectively assess the laryngeal vibratory behavior, endoscopic high-speed cameras capture several thousand frames per second of the vocal folds during phonation. However, judging all inherent clinically relevant features is a challenging task and requires well-founded expert knowledge. In this study, an automated wavelet-based analysis of laryngeal high-speed videos based on phonovibrograms is presented. The phonovibrogram is an image representation of the spatiotemporal pattern of vocal fold vibration and constitutes the basis for a computer-based analysis of laryngeal dynamics. The features extracted from the wavelet transform are shown to be closely related to a basic set of video-based measurements categorized by the European Laryngological Society for a subjective assessment of pathologic voices. The wavelet-based analysis further offers information about irregularity and lateral asymmetry and asynchrony. It is demonstrated in healthy and pathologic subjects as well as for a surgical group that was examined before and after the removal of a vocal fold polyp. The features were found to not only classify glottal closure characteristics but also quantify the impact of pathologies on the vibratory behavior. The interpretability and the discriminative power of the proposed feature set show promising relevance for a computer-assisted diagnosis and classification of voice disorders.

A multiscale product approach for an automatic classification of voice disorders from endoscopic high-speed videos

Direct observation of vocal fold vibration is indispensable for a clinical diagnosis of voice disorders. Among current imaging techniques, high-speed videoendoscopy constitutes a state-of-the-art method capturing several thousand frames per second of the vocal folds during phonation. Recently, a method for extracting descriptive features from phonovibrograms, a two-dimensional image containing the spatio-temporal pattern of vocal fold dynamics, was presented. The derived features are closely related to a clinically established protocol for functional assessment of pathologic voices. The discriminative power of these features for different pathologic findings and configurations has not been assessed yet. In the current study, a collective of 220 subjects is considered for two- and multi-class problems of healthy and pathologic findings. The performance of the proposed feature set is compared to conventional feature reduction routines and was found to clearly outperform these. As such, the proposed procedure shows great potential for diagnostical issues of vocal fold disorders.

A wavelet-based approach for a continuous analysis of phonovibrograms

Recently, endoscopic high-speed laryngoscopy has been established for commercial use and constitutes a state-of-the-art technique to examine vocal fold dynamics. Despite overcoming many limitations of commonly applied stroboscopy it has not gained widespread clinical application, yet. A major drawback is a missing methodology of extracting valuable features to support visual assessment or computer-aided diagnosis. In this paper a compact and descriptive feature set is presented. The feature extraction routines are based on two-dimensional color graphs called phonovibrograms (PVG). These graphs contain the full spatio-temporal pattern of vocal fold dynamics and are therefore suited to derive features that comprehensively describe the vibration pattern of vocal folds. Within our approach, clinically relevant features such as glottal closure type, symmetry and periodicity are quantified in a set of 10 descriptive features. The suitability for classification tasks is shown using a clinical data set comprising 50 healthy and 50 paralytic subjects. A classification accuracy of 93.2% has been achieved.

Phonovibrography: The Fingerprint of Vocal Fold Vibrations

A new approach for quantitative and objective analysis of vibration patterns of the vocal folds is presented. Vocal fold vibrations are recorded during sustained phonation in real time using a digital high-speed system coupled to a rigid endoscope. Within these high-speed movies, the edges of the oscillating vocal folds are detected by an adapted region-growing algorithm. The used segmentation algorithm is evaluated regarding its stability and correctness within 372 recordings proofing its clinical applicability. From the segmented vocal fold edges, a two-dimensional color encoded matrix is performed, visualizing the oscillations of the entire vocal fold edges over time. These created so called phonovibrograms allow a direct and objective view on the occurring laryngeal dynamics. The phonovibrograms can be used for assessing therapy progress and as a basis for further classification of different types of dysphonia. Phonovibrograms have the potential to serve as the first standard in endoscopic high-speed evaluation of vocal fold dynamics.