Residual ocular artefact subsequentto ocular artefact removal fromthe electroencephalogram

A method based on the vector representation of electro-oculogram (EOG) and electroencephalogram (EEG) signals has been developed for quantifying in simulation the amount of residual ocular artefact (OA) contamination of EEGs after the application of an EOG-based OA removal (OAR) algorithm. The residual artefact is measured as R2, the ratio of residual OA power to the estimated background EEG power. Two types of OA model, the in-plane and the out-of-plane model, were introduced. Values of R2 were computed using simulated contaminated EEGs, which were constructed using measured EEGs, contaminated by a variety of eye movements and blinks, and measured EOG signals. In most cases the estimate of R2 was approximately 0.03, corresponding to a 17% modification of the EEG voltage. The radial component contributed up to 30% of the residual artefact power. For practical applications, the use of the vertical and horizontal right and the radial EOG components was found to be preferred.