The human eye can be perceived as a dipole with the positive pole at the front of the eye and the negative pole at the back. The corneo-retinal potential elicited from this dipole is called the EOG. Any eye movement or blinks will result in a potential spread that will be recorded by all EEG electrodes in the form of signal offsets and transients. While an eye movement changes the direction of the corneo-retinal dipole and elicit an artifact that is roughly linearly dependent with the movement size and direction, a blink creates a “short-circuit” between the cornea and the extra ocular skin and elicits a monophasic deflection of 50-100 µV in the EEG channels.
A typical approach to record an EOG signal is to use a bipolar montage, where one pair of electrodes is used to record horizontal eye movements (HEOG) and a second pair of electrodes is used to record vertical eye movements (VEOG). The respective position of each electrode is illustrated in Figure 1.
Here, HEOG is acquired by placing one electrode at the canthus of one eye (positive site) and the second electrode at the canthus of the other eye (negative site). The placement of one electrode below and another above the eye allows the recording of VEOG.
Based on the above characteristics of the EOG, Brain Products offers different solutions to achieve a good EOG signal. In what follows, we will describe how to record an EOG signal using actiCHamp and how to set up a Recorder workspace based on the method chosen.