EEG activity was recorded from three channels (P3, PZ, P4) using an electrode cap and linked earlobes as the reference. Sensors placed on the outer canthus and above one eye recorded eye movements (EOG). A ground electrode was placed on the right shin. The electrode impedance was kept below 5 Kohms for EEG and 10 Kohms for the EOG and ground. Data were recorded on a Grass Model 12A Neurodata acquisition system with a ½ amplitude low and high frequency filter settings at .01 Hz and 30 Hz, respectively. The EEG was digitized on line at a rate of 256 samples/second over a 500 ms baseline and a 1500 ms post baseline epoch. A standard eye-blink correction algorithm was applied to remove ocular artifacts from the raw EEG data (Gratton, Coles, & Donchin, 1983) and a 7.5 Hz low pass digital filter was applied to reduce high frequency noise. Analog-to-digital saturation led to repetition of trials.
