Electroglottographic Waveform Research Articles

Approximations of open quotient and speed quotient from glottal airflow and EGG waveforms: effects of measurement criteria and sound pressure level.

Noninvasive measures of vocal fold activity are useful for describing normal and disordered voice production. Measures of open and speed quotient from glottal airflow and electroglottographic (EGG) waveforms have been used to describe timing events associated with vocal fold vibration. To date, there has been little consistency in the measurement criteria used to calculate quotient values. In this study, criteria of 20% and 50% were applied to the AC amplitude of glottal airflow and inverted EGG waveforms for measurement of open quotient. Criteria of 20%, 50%, and 80%, and a midslope criterion that segmented the waveform between 20% and 80% of the waveform amplitude, were used for the calculation of speed quotient. Subjects produced waveforms at sound pressure levels (SPL) of 70, 75, 80 and 85 dB. Results indicated that approximations of open quotient obtained from the glottal airflow waveform significantly decreased using both the 20% and 50% criteria as SPL increased from 80 to 85 dB. No significant changes were found in open quotient from the EGG waveform as a function of SPL. Results of speed quotient measures from the glottal airflow and EGG waveforms showed a generally increasing trend as SPL increased, although the differences were not statistically significant. The data suggest that the signal type, measurement criterion and SPL must be considered in interpreting quotient measures.

Electroglottography and laryngeal articulation in speech.

Electroglottography (EGG) has been used for investigating the functioning of the vocal folds during vibration. EGG is related to the patterns of vocal fold vibration during phonation and characterizes the temporal patterns of each vibratory cycle. The purpose of this study was to investigate the dynamic changes in EGG waveforms during continuous speech. Aerodynamic signals, air pressure and airflow were evaluated simultaneously with EGG waveforms. Fundamental frequency (F0), open quotient (OQ) and baseline shift of the EGG during speech production were measured for three types of Korean consonants using EGG waveforms. The glottal airway resistance during speech production was measured using aerodynamic waveforms, and evaluated for the relationship with F0, OQ and baseline shift. The results indicated that the EGG waveforms seem to be significantly affected by the articulatory activities of the larynx, airflow and subglottic pressure, and may be a useful method to describe dynamic laryngeal articulatory activity during continuous speech.

Laryngeal movement, oropharyngeal pressure, and submental muscle contraction during swallowing

This study examined temporal relationships of laryngeal movement, oropharyngeal pressure and submental muscle contraction during swallowing. Techniques used to obtain the temporal measures were electroglottography (EGG), oropharyngeal manometry, and submental surface electromyography. Liquid bolus swallows were performed by 40 normal subjects evenly divided by young and elderly, men and women. Results of this investigation suggest that the EGG waveform is reflective of the temporal aspects of laryngeal movement during swallowing and that the EGG has potential as a behavioral modification technique in swallowing therapy. A case study is presented to illustrate the use of the electroglottograph for biofeedback.

Effect of asymmetric vocal fold stiffness on traveling wave velocity in the canine larynx.

The vocal fold (VF) traveling wave is essential to normal voice production. The present investigation describes a new method to determine traveling wave velocity (TWV) in the in vivo canine phonatory model. This method synchronizes photoglottographic and electroglottographic waveforms with videostroboscopic images to determine the duration of time the traveling wave moves between two tattoos placed a known distance apart between the upper and lower margins of each VF. Using this method, we compared the TWV of a paralyzed VF with the TWV of the contralateral, electrically stimulated VF during phonation in two canines. In addition, the presumed VF stiffness asymmetry in the simulated acute recurrent laryngeal nerve paralysis state was confirmed by measuring Young's modulus of each VF. The results indicated that the TWV of the paralyzed VF averaged 55% of the TWV of the normal, stiffer VF when the glottal gap was small and entrainment occurred. This study demonstrated the feasibility of quantifying traveling wave motion in asymmetric VF stiffness disorders. The potential use of TWV in human beings as a target to optimize the phonosurgical results in asymmetric VF stiffness disorders is discussed.

Videostroboscopy of human vocal fold paralysis.

Previous stroboscopic studies of human vocal cord paralysis have been infrequent and have lacked documentation of the site of lesion. In order to study human laryngeal paralysis, the recurrent and superior laryngeal nerves were infiltrated unilaterally with lidocaine hydrochloride in three human volunteers. Vagal paralysis was simulated by combined (superior and recurrent) infiltration in one volunteer. Additionally, 20 patients with untreated laryngeal paralysis were studied from the voice laboratory at UCLA. In addition to videostroboscopic analysis, photoglottography and electroglottography were performed and synchronized with the stroboscopic images. The most significant finding in stroboscopy of the paralyzed larynx was the asymmetry of traveling wave motion. The traveling wave on the normal vocal fold had a faster wave velocity that created a phase difference in the vibration of the two folds. The wave also traversed a greater distance along the vocal fold mucosa on the normal side. No patient or volunteer with untreated laryngeal paralysis had a symmetric traveling wave, either in superior or recurrent laryngeal nerve paralysis. Synchronization with glottography indicated that the differentiated electroglottographic waveform provides useful information about the timing of glottic opening and closure in states of asymmetric laryngeal vibration. Implications for future studies and for the diagnosis of laryngeal paralysis are discussed.

Characterization of the electroglottographic waveform: a primary study to investigate vocal fold functioning.

To objectify the vocal fold functioning we opted for a method of processing the electroglottographic (EGG) signal. This study with 7 normal and 12 pathological voices presents the results of measurements over the chest register as a function of voice intensity and frequency. Reproduction measurements show that at least 5 measurements per intensity/frequency pair are needed to get a reasonable estimation of the EGG parameters. The averaged results over about 20 measurements in the chest register showed differences for some parameters for subjects in the most different categories. To get more consistent results we recommend to improve the measurement protocol and adjust the parameters.

An automated method for matching a vocal fold contact area model to an EGG waveform

Electroglottography (EGG) signals arc routinely used for observation of vocal fold adduction and regularity in vocal fold vibration. Analysis over many cycles can be very tedious if waveform parameters arc extracted manually or semiautomatically. A parameter optimization strategy is used here to provide a list fit to a model, thereby allowing larger volumes of data to be processed. Processing speed and reliability of extraction depend on the type of model being used and the cleverness in choosing the appropriate seed values. [Work supported by NIH.]

Interpretation of the electroglottographic signal

Summary Interpretation of the electroglottographic (EGG) signal involves at least two major stages of investigation, the transduction stage and the modeling stage. This article addresses some aspects of both of these stages. In the transduction stage, it is shown how electrode size and orientation can affect the signal-to-noise ratio and the linearity of the EGG signal. Best results are predicted when interelectrode distance is small, electrode size is on the order of the glottal length, and the electrode angle is small. In the modeling stage, it is shown that pulse widening of the EGG waveshape results from increased adduction, that peak skewing results from glottal convergence (in the presence of vertical phasing), the knee in the EGG waveform results from medial surface bulging, and gradual sloping of the waveform (toward a triangular shape) results from increased vertical phasing.

Synchronized videostroboscopic and electroglottographic examination of glottal opening.

Interpretation of electroglottography (EGG) as an index of glottal contact area has been complicated by difficulty obtaining independent validation measures. The purpose of this research was to implement a new simultaneous EGG/videostroboscopic technique for the evaluation of the relationship between a discontinuity in the opening phase of the EGG waveform with the onset of glottal opening viewed via videostroboscopy. The results support previous suggestions that this EGG discontinuity, when observed in nonpathologic individuals, usually marks the onset of glottal opening along the superior surface of the vocal folds.

Conditioned variability in voicing offsets

The authors amplify observations by A.K. Krishnamurthy and D.G. Childers (ibid., vol.ASSP-34, p.730-43, Aug. 1986) regarding speech pressure and electroglottographic waveform characteristics at the cessation of voiced speech. They pointed out the great variability in both the abruptness of voicing offset and in the temporal relations of these waveforms at offset. The present authors report that their data confirm that the situation described by Krishnamurthy and Childers occurs frequently. They also report that there can be a decrease in the sharpness of closure of the vocal folds in the final cycles, so that the laryngeal vibration, while causing substantial deflection in the Lx waveform, generates little acoustic energy. This correlates auditorily with a relatively breathy offset, and with an increase in the duration of the open phase with respect to the closed phase of the glottal cycle. >

Laryngeal modeling: Theoretical, in vitro, in vivo

Because the larynx is situated anatomically in an area which is difficult to measure and visualize, theoretical, in vitro, and in vivo models are used in laryngeal research. Vocal fold vibration was studied in anesthetized dogs, while electrically stimulating independently the superior and recurrent laryngeal nerves under conditions of constant airflow. Photoglottographic (PGG), electroglottographic (EGG), and subglottic pressure signals were obtained while stroboscopically photographing the larynx. Specific points along PGG, EGG, and subglottic pressure waveforms were correlated with laryngeal events which occurred during vibration. The canine larynx, in an experimentally produced phonatory mode, vibrates in a two mass (upper and lower margin) system and appears comparable to modal human voice production. The recorded glottographic waveforms from experimentally produced phonation in the canine are similar to signals recorded from humans. However, observed differences can be related to anatomic differences.

An electroglottographic study of vocal vibrato

Summary This study investigated vocal vibrato in trained singers through the use of electroglottography (EGG). Ten adult trained singers (7 women, 3 men) were each required to produce four singing tasks. The tasks involved the production of / a / during an ascending interval of a third in both chest and falsetto registers, once with and once without vibrato. Audio and EGG output during these tasks were directly digitized for subsequent analysis. Results pertaining to changes in the EGG waveform as a function of the singer's gender, the vocal register and the vibrato condition are discussed. A major finding was the apparent absence of consistent, distinctive differentiation in the EGG waveforms when comparing the vibrato and vibrato-inhibited conditions for the majority of subjects. Possible explanations for the majority findings, as well as comment on the feasibility of the EGG for investigating vocal vibrato, are discussed.

Vocal fold vibrations in dysphonia: model vs. measurement

Several investigators have conjectured that the electroglottographic (EGG) waveform is inversely proportional to the lateral area of contact of the vocal folds. But this conjecture is essentially impossible to substantiate by observations. We have developed a simple model of the vocal folds that estimates the vocal fold lateral contact area as a function of time. The EGG waveform is directly calculated as the reciprocal of this lateral contact area function. We show how the model may be used to simulate EGG waveforms for normal male voices in model register and vocal fry and for predicting EGG waveforms for models of vibrating vocal folds that have a nodule or polyp on one fold.

Onset of voicing in stuttered and fluent utterances.

Electroglottographic (EGG) and acoustic waveforms of the first few glottal pulses of voicing were monitored and voice onset time (VOT) measured during an adaptation task performed by stutterers and controls. The fluent utterances of stutterers resembled those of control subjects. After dysfluencies, however, the EGG signal increased gradually, lending physiological support to the technique of "easy onset" of voicing. EGG waveforms also served to help differentiate mild from severe stutterers. Idiosyncratic ritualized laryngeal behavior, sometimes including physiological tremor, was evident in the EGG record.

Electroglottography for laryngeal function assessment and speech analysis.

The methodology of electroglottography is briefly outlined, Major emphasis is given to validating key features of the electroglottographic (EGG) waveform using ultrahigh-speed laryngeal films. We show how the instants of glottal closure and opening may be identified from the EGG waveform. This information may be used to improve speech analysis techniques such as the pitch synchronous, closed phase, covariance analysis method. Other applications include pitch detection, the determination of intervals of voicing, unvoicing, mixed voicing and silence, improving speech synthesis, and assisting the automation of inverse filtering.

Relationships between electroglottograph, speech, and vocal cord contact.

Our research involves laryngeal assessment via the analysis of data obtained from simultaneously recorded electroglottographic waveforms, acoustic signals, and ultra-high-speed laryngeal films, which have all been synchronized by special timing signals. We report results which support the fact that the output of an electroglottographic device does indeed reflect vocal fold contact. Further, periodicity analysis performed on the speech and electroglottographic data, synchronously recorded for the same utterance, yield equivalent measures. The data were obtained from both normal subjects and patients with various pathologies and vocal disorders.

Mathematical models of glottal area and vocal fold contact area

The glottal area function and the vocal fold contact area are computed as a function of a dynamically changing glottal configuration. Parameters are prephonatory widths and amplitudes of vibration of the upper and lower margins of the vocal folds, and the phase angle between the two. The computed waveforms are compared with measured photoglottographic (PGG) and electroglottographic (EGG) waveforms. The basic PGG and EGG waveform shapes are confirmed by modeling, although a simple relationship between vocal fold contact area and EGG may not always exist. It is demonstrated that symmetries in these glottographic waveforms are related to the shape of the medial surface contour of the vocal fold and should not be confused with asymmetries in the glottal volume flow [Rothenberg, Vocal Fold Physiology, edited by Stevens and Hirano (1981), pp. 305–323].