THE EFFECT OF SMALL DIFFERENCES IN ELECTRODE POSITION ON EOG SIGNALS - APPLICATION TO VIGILANCE STUDIES

The primary aim of the study was to determine the best electrode posit ions for EOG signals in vigilance studies. Two-channel recordings were conducted in analogy to the Rechtschaffen and Kales (1968) system. Tw enty electrodes (10 electrode pairs) were compared. Both EOG amplitude s and amplitude asymmetries within an electrode pair were studied. The amplitude of the EOG signal is sensitive to relatively small differen ces in electrode position. This concerns especially distance from the eye, the direction of eye movement and the effect of the upper eye lid movement. Larger and more symmetrical EOG amplitudes were obtained fo r different eye movements by placing the electrodes more medially than in the conventionally used system. EOG asymmetry in different electro de positions was dependent on the eye movement direction and even on t he starting and end points of a movement with equal angular degrees. M ost of the data could be explained by a simple monopolar model when co mbined with the effects of the upper eye lid movements. The most unexp ected finding was that the EOG amplitudes of the horizontal and obliqu e eye movements were significantly larger when the eyes were moving to wards an electrode than when they were moving to the opposite directio n.