The EEG was recorded with a Biosemi Active-Two system using sintered Ag/Ag-Cl electrodes in an electrode cap at 71 standard scalp sites (DC–100 Hz bandpass filter, 512 Hz digitization rate). The DC offsets were kept below 25 mV. During data acquisition, all channels were referred to the system’s internal loop (CMS/DRL sensors located in the parietal region) and offline re-referenced to the left mastoid electrode. The bipolar vertical electro-oculogram (EOG) was derived from electrode Fp1 and an electrode below the left eye. The horizontal EOG was derived from electrodes on the left and right outer canthi.
