The ERFIA multilevel method.

The processing steps from the ‘raw’ EEG to ERFIAs serving as the dependent variable for multilevel analysis. First, the EEG is partitioned into event-related segments, and then a baseline correction is made. Next, the segments are partitioned in 20-ms intervals, and the area under the curve for every interval for all trials is calculated. As a third step, an EOG rejection is carried out for all ERFIAs separately. Finally, the valid ERFIAs per fixed interval serve as a dependent variable in the multilevel analysis.