Electroglottograph

The electroglottograph, or EGG, (sometimes referred to as a laryngograph) is a device for the noninvasive measurement of the time variation of the degree of contact between the vibrating vocal folds during voice production. Though it is difficult to verify the assumption precisely, the aspect of contact being measured by a typical EGG unit is considered to be the vocal fold contact area (VFCA). To measure VFCA, an EGG records variations in the transverse electrical impedance of the larynx and nearby tissues by means of a small A/C electric current in the megaHertz region applied by electrodes on the surface of the neck. This electrical impedance will vary slightly with the area of contact between the moist vocal folds during that part of the glottal vibratory cycle in which the folds are in contact. 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.