Electroglottography

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The electroglotto graphie (EGG) (Greek glôttis - the vocal apparatus consisting of both vocal cords, glottis) - also called electrolaryngography, ELG ; (Greek larynx ) - is a procedure for observing, measuring and visualizing the activity of the larynx during normal and impaired speech. The vibration cycle of the vocal folds is shown . The recording device is the laryngograph . The graphically recorded EGG or ELG (electroglottogram or electrolaryngogram) gives both quantitative and qualitative information about vocal fold vibration and the linguistic use of the voice.

Function and application

Electroglottography (electrolaryngography) shows the functionality of the vocal folds in the larynx area during phonation (speaking, singing, loud singing). It provides information about the course of vocal fold vibrations and is therefore suitable for larynx and vocal cord diagnostics and for monitoring the course of larynx and vocal cord treatments and voice therapies. In particular, the course of treatment for organic voice disorders can be easily evaluated and documented with electroglottography. A great advantage of electroglottography is the direct and non-invasive measurement of vocal fold movement. A direct vocal fold signal can thus be measured by measuring devices without restricting phonation.

Electroglottography is used in clinical practice

  • EGG has already been used with positive results for the deaf and hearing impaired
  • it is also used in dysphonia (voice disorder) and, through electrocochlear stimulation in people with acquired deafness, a prosthesis for lip reading is obtained from the recorded EGG

Investigation procedure and evaluation

During an EGG examination, two surface electrodes are placed symmetrically over the two wings of the thyroid cartilage . During phonation, the impedance of the vibrating vocal folds is measured between the electrodes . A so-called Lx-Laryngographic signal is available as a measurement file, which shows the horizontal opening and closing movement of the vocal folds. Modern devices also allow the synchronous recording of the voice via a microphone, so that the Lx signal (vocal fold vibration) can also be compared directly with the vocal sound. The recording of electrical impedance, which forms the basis of electroglottography, was introduced by Fabre (1957), albeit in a slightly different form.

The so-called Lx waveform recorded during an EGG (ELG) examination ( Lx is the name for the recorded laryngogram; see Laryngograph ) is in the positive range for the increasing vocal fold closure and each peak corresponds to the maximum contact between the vocal folds. The main edge of the waveform gives a precise indication of the beginning of the closing phase. The Lx waveform does not give any explicit information about the opening width of the glottis . Abberton / Fourcin therefore call the EGG electrolaryngography: 'A true glottograph would give information about the glottis , i.e. about the volume between the vocal folds.

Lx waveforms

The vocal cord vibration is a complex three-dimensional movement. The horizontal opening and closing movements of the vocal folds to and from the midline are more common because they are relatively easy to observe. The vertical component of the vibratory cycle is less well described.

Abnormal Lx waveforms

Lx waveforms occur when there are physical abnormalities or medical disorders of the voice.

Normal vocal folds

  • same mass and hardness, mucus layer consistently tough and shiny.

Abnormal voice

  • Continuously irregular or incomplete vibration or short sections of abnormal or irregular vibration (also perceptible in the auditory impression)
  • usually occurs with the main pitch changes or in connection with certain oral articulation processes (e.g. with velar consonants)
  • Disturbance of the air flow aerodynamics
  • no symmetrical vocal cord vibration

pathological vocal folds

  • larger mass of a vocal cord: ( polyp or carcinoma )
  • Differences in stiffness due to unilateral paralysis.

Vocal cords in laryngitis

  • different levels of mucus on both lips or particular dryness of the vocal folds

EGG in pathological speech

Abberton and Fourcin assume that the electroglottograph is well suited for evaluating voice production because of the direct reproduction of cyclical vocal fold vibration. Disturbances in voice formation are very likely to be closely related to the closing and closed phases of vocal fold vibration.

EGG and other methods

  • Classic indirect laryngoscopy:

Visual procedure, involves inserting a mirror in the throat and sticking out the tongue: only artificial vowel sound can be produced. (Larynxoscopy with a mirror or magnifying endoscope, sometimes with local anesthesia of the pharynx against the gag reflex)

  • Direct laryngoscopy: (autoscopy)

Introduction of a supporting laryngoscope and an endoscope , which can also be connected to a microscope. Recognizable: color of the mucous membrane, changes, deposits and mobility of the vocal folds visible, also paralysis, carcinoma

  • Laryngostroboscopy:

Laryngostroboscopy generates short flashes of light at regular intervals, the frequency of which can be changed. These are superimposed (synchronized) with the vibrations of the vocal folds via a larynx microphone: the impression of an apparent standstill occurs. When the lightning frequency is changed, a strongly slowed oscillation sequence can be made visible. In these procedures, only the surface of the vocal folds is visible, while the vertical component of the vocal fold vibrations cannot be clearly observed.

One advantage of electroglottography over these methods is that EGG does not require complex procedures for evaluating the acoustic speech signal and there is no need to intervene in the speech process.

literature

  • E. Abberton, AJ Fourcin: Electroglottography. In: Experimental clinical phonetics. Ed .: C. Code, M. Ball, Billing & Sons, Worcester 1984, 62-78
  • N. Henrich, B. Roubeau, M. Castellengo: On the use of electroglottography for characterization of the laryngeal mechanisms . Proc. Stockholm Music Acoustics Conf., 2003, Stockholm, Sweden, pp. 455–458 ( available online here )

See also