Eye movement-related artefact in the EEG causes serious
dif®culties in the interpretation of EEG (as is described
more fully in Croft and Barry, 1998a). One method of reducing
this problem is to remove the ocular voltage from the
EEG using EOG correction techniques. For example in Eq.
(1) the true EEG (estTEEG) at time point (i) is estimated as
the measured EEG (MEEG) minus a proportion (B) of the
voltage measured about the eyes (Gratton et al., 1983). B is
typically calculated separately for each subject and scalp
site using Eq. (2) (the least squares method), where X and
Y are the EOG and EEG voltages, respectively, at time i.
With the use of such a procedure, the experimenter does not
have to reject data contaminated by ocular artefact.