Removal of ocular artifact from the EEG: a review

Eye movements cause changes to the electric fields around the eyes, and consequently over the scalp. As a result, EEG recordings are often significantly distorted, and their interpretation problematic. A number of methods have been proposed to overcome this problem, ranging from the rejection of data corresponding temporally to large eye movements, to the removal of the estimated effect of ocular activity from the EEG (EOG correction). This paper reviews a number of such methods of dealing with ocular artifact in the EEG, focusing on the relative merits of a variety of EOG correction procedures. Issues discussed include the distinction between frequency and time domain approaches, the number of EOG channels required for adequate correction, estimating correction coefficients from raw versus averaged data, differential correction of different types of eye movement, the most suitable statistical procedure for estimating correction coefficients, the use of calibration trials for the estimation of correction coefficients, and the distinction between 'coefficient estimation' and 'correction phase' error. A suggested EOG correction algorithm is also described.