Removal of ocular artifact from the EEG: a review

Eye movements cause changes to the electric fields around the eyes, and con sequently over the scalp. As a result, EEG recordings are often significant ly distorted, and their interpretation problematic. A number of methods hav e been proposed to overcome this problem, ranging from the rejection of dat a corresponding temporally to large eye movements, to the removal of the es timated effect of ocular activity from the EEG (EOG correction). This paper reviews a number of such methods of dealing with ocular artifact in the EE G, focusing on the relative merits of a variety of EOG correction procedure s. Issues discussed include the distinction between frequency and time doma in approaches, the number of EOG channels required for adequate correction, estimating correction coefficients from raw versus averaged data, differen tial correction of different types of eye movement, the most suitable stati stical procedure for estimating correction coefficients, the use of calibra tion trials for the estimation of correction coefficients, and the distinct ion between 'coefficient estimation' and 'correction phase' error. A sugges ted EOG correction algorithm is also described. (C) 2000 Editions scientifi ques et medicales Elsevier SAS.