A Grass model 12A Neurodata Acquisition System recorded EEG and electrooculographic (EOG) data at a sampling rate of 256 Hz and filtered from 0.01 – 30 Hz (6 dB/octave rolloff). EEG, referenced to linked earlobes, was recorded from three parietal electrodes: on the midline at Pz, and over left and right hemispheres at P3 and P4, respectively. EOG was recorded using a pair of biopotential electrodes arranged in a transverse montage, one electrode placed superior to the eye and the other at the outer canthus. Impedances were kept below 5 kΩ for EEG and below 10 kΩ for EOG. Trials consisted of 2 s of data, including a 500 ms prestimulus baseline. Target trials were repeated if the subject failed to respond or the analog-to-digital converter’s limits were exceeded. Two standard trials were presented before each repeated target trial to maintain a constant proportion of target and standard trials. Trials repeated more than twice were excluded from averaging.
