Electroglottograph

The electroglottograph, or EGG, (also referred to as a laryngograph) is a device used for the noninvasive measurement of the degree of contact between the vibrating vocal folds during voice production.

[1][2] To measure VFCA, electrodes are applied on the surface of the neck so that the EGG records variations in the transverse electrical impedance of the larynx and nearby tissues by means of a small A/C electric current (in megaHertz).

However, because the percentage variation in the neck impedance caused by vocal fold contact can be extremely small and varies considerably between subjects, no absolute measure of contact area is obtained, only the pattern of variation for a given subject.

In addition, by using multiple channels simultaneously, the technique can be made easier to use and more reliable by giving the user an indication of the correct positioning of the electrodes, and providing a quantitative measure of vertical movements of the larynx during voice production.

This technique provides an intuitive means for quickly assessing vocal fold contact phenomena and their variation over time.

Electroglottograph, Glottal Enterprises model EG2-PCX shown here.
Photograph of an EGG signal from a Glottal Enterprises EG2-PC (top) and a Laryngograph/Kay electroglottograph (bottom).
Showing the contacts on the electrodes from a Glottal Enterprises EG2-PCX. Electrodes for other electroglottographs are typically very similar in size and shape. This set of electrodes is from a Glottal Enterprises EG2-PCX, which is a dual-channel EGG, so it has 2 sets of contacts. Electrode jelly is used to help conduct the signal from the contacts to the neck.
Figure 7 of: Martin Rothenberg and James J. Mashie, Monitoring Vocal Fold Abduction Through Vocal Fold Contact Area Journal of Speech and Hearing Research, Volume 31, 338-351, September 1988