After acquisition, raw data were referenced to nose, bipolar horizontal and vertical EOG derivations were computed from the four eye channels, and converted to 16-bit Neuroscan format after removing ActiveTwo DC offsets using Polyrex software (Kayser, 2003). Also during this stage, a second degree Polynomial high pass filter spanning an entire recording block (approximately 5 min) was applied, which empirically outperforms other high pass filter algorithms commonly used to reduce or eliminate DC drifts. Volume-conducted blink artifacts were effectively removed from the filtered, continuous EEG by means of spatial PCA generated from identified blinks and artifact-free EEG periods (NeuroScan, 2003).
