Continuous electroencephalogram (EEG), stimulus onset, and response codes were recorded using a 72-channel, 24-bit Biosemi ActiveTwo system (256 samples/s; DC-128 Hz). After acquisition, raw data were converted to a nose reference, bipolar EOG derivations were computed from the four eye channels (horizontal electrooculgram (HEOG) = RE – LE; vertical electrooculogram (VEOG) = TE – BE) and exported to 16-bit Neuroscan format using Polyrex (Kayser, 2003), a widely used conversion program that removes ActiveTwo DC offsets, optimizes data rescaling for 16-bit resolution, and provides EEG re-referencing. Amplifier drift was eliminated by padding sufficient samples into the beginning of the file and applying a high-pass causal filter based a rectangular smoothing window (3541-point padding/channel allows the buildup of a rectangular filter window, corresponding to a 10-s time constant2). The filtered, continuous EEG was then blink corrected using a spatial, singular value decomposition filter generated from identified blinks and artifact-free EEG periods (NeuroScan, 2003).
