2.1.3. EEG recording and quantification
EEG was recorded using a Quick-Cap with sintered electrodes. Using the Ten-twenty Electrode Placement System of the International Federation, the EEG activity was monitored over nineteen scalp locations. All leads were referenced to linked mastoids (M1 and M2), and a ground electrode was applied to the forehead. Additionally, vertical eye movements were recorded with electrodes placed above and below the left eye. The 19 EEG traces were digitized online at 1000 Hz and stored on a hard disk. Epochs were comprised from the 3000 ms preceding and 8000 ms following the stimulus presentation and automatically screened for artifacts. Excluded were all epochs showing amplitudes above ±50 μV. All together 2.1% of epochs were excluded from further analysis.