Electrolaryngography (Lx) and electroglottography (EGG) are non-invasive methods used to assess human vocal fold vibration and investigate speech and singing. This paper provides a systematic review of evidence-based studies using Lx/EGG in the analysis of the singing voice, identifying and critically appraising the thematic content and the research methodologies of the relevant investigations. Lx/EGG represents a powerful tool for the analysis of the singing voice in medical settings, and in support of research and teaching. Current research in this area is paving the way towards a better comprehension of singing performance.
Electrolaryngography (Lx) and electroglottography (EGG) are non-invasive techniques for assessing human vocal folds, through the application of electrodes placed externally on either side of the neck. Developed by Fabre, the basic principle of EGG was reported in Fabre (1940) and fully explained in Fabre (1957). The tool was further developed by Fourcin and Abberton (1971), who presented a slightly different version, the Lx, and by Rothenberg (1992), who designed the multichannel EGG, featuring a vertical array of two pairs of electrodes to track the vertical movements of the larynx.
Based on the principle that human tissue is a good electrical conductor while air is not, the Lx/EGG electrodes monitor the closing and opening of the vocal folds (see Figure 1), by measuring variations in the electrical impedance of the larynx. A constant, high frequency current in the 0.3-3MHz range is sent through the neck of the participant using the electrodes: the impedance/admittance variation of the current, caused by the contacting and de-contacting of the vocal folds, is measured (Fourcin & Abberton, 1971), which reflects the amount of contact between the vocal folds (Scherer, Druker, & Titze, 1988) and is graphically represented in the waveform produced.