Data processing was conducted in MATLAB® (2009a, The Mathworks, Natick, MA) using identical methods for both systems, based on functions in the Psychophysiology Toolbox (http://sourceforge.net/projects/psychophys/) and custom scripts. Biosemi data were transformed to be comparable to the original data. Data were downsampled using the Matlab resample function. The signal from Cz was referenced to an algebraic average of the two ears, whereas the signals from O1 and O2 were referenced to P7 and P8, respectively. All signals were filtered with finite impulse response (FIR) filters and a Kaiser window as implemented in the firfilt plugin to EEGLAB (Delorme & Makeig, 2004): a highpass filter with a half-amplitude cutoff frequency of 1 Hz (1-Hz transition band, filter order of 1286, ripple of .0001) and subsequently a lowpass FIR filter with a half-amplitude cutoff frequency of 30 Hz (transition band of 20 Hz, filter order of 24, ripple of .0001). A transverse EOG lead was created from the appropriate pair of monopolar electrodes.
