The Correction of EOG Artifacts by Frequency Dependent and Frequency Independent Methods

Methods for correcting EEG which is contaminated by EOG artifacts, which are frequency dependent or frequency independent, were compared. EEG activity contaminated mainly by eye movements was treated separately from activity contaminated mainly by blinks. The statistical comparison was based on representative, real data incorporating differential effects over frequency. The influence of EOG activity on different derivations and bands, and the resulting need for correction of EOG artifacts were of interest too. Correction using a constant gain function proved to be consistently inferior to using a gain depending on frequency. For eye movements, differences were, however, not very large in practical terms, and this was true for all frequency bands. The correction of blinks by the time domain method (i.e., constant gain) may become misleading in the sub-delta band, which might have implications for very slow activity such as slow cortical potentials. Transfer functions not corrected for coherent EEG activity at the EOG electrodes overcompensated in the alpha and beta bands, in line with earlier results showing the need to incorporate coherent EEG activity into the determination of EOG-EEG transfer. It was found to be preferable to use sample average coefficients and gain functions, rather than individual ones, leading also to simpler computing. EOG correction is indispensable at frontal derivations, in particular for the delta and theta bands. It is advisable to correct at central and even at parietal derivations.