Fig. 11. The basis of the electro-oculogram (EOG). Subjects are seated before a cupola as portrayed in Figure 9. Skin electrodes are placed near the inner and outer canthi for recording the EOG. At regular intervals, the patient is required to move his or her eyes back and forth through an excursion of 30 degrees. In the cupola portrayed in Figure 9, this would be the distance between the two outer light-emitting diodes. Typically, EOG recording is bilateral. (Adapted from a figure provided by Metrovision, Pérenchies, France: http://www.metrovision.fr.)