Electroencephalographic data were recorded from a 64-electrode scalp cap using the 10–20 system (Brain Products, Munich, Germany) with reference electrodes on the left and right mastoids. The vertical electrooculogram (EOG) was recorded with placed above and below the left eye. EEG and EOG activity was amplified at 0.01–100 Hz band-pass and sampled at 500 Hz. All of the electrode impedances were maintained below 5 kΩ.
The EEG data were pre-processed and analyzed using Matlab R2011b software (MathWorks) and the EEGLAB toolbox (Delorme and Makeig, 2004 (link)). The EEG data for each electrode were down-sampled to 250 Hz and re-referenced to the grand averages. The signal was then passed through a 0.01- to 30-Hz band-pass filter. Time windows of 200 ms before and 700 ms after the onset of the picture were segmented. EOG artifacts were corrected using an independent component analysis (ICA) (Jung et al., 2001 (link)) (Supplementary Figure S1 ). Epochs with amplitudes that exceeded ±50 μV at any electrode were excluded from the average (5.6 ± 0.6% trials were excluded).
The EEG data were pre-processed and analyzed using Matlab R2011b software (MathWorks) and the EEGLAB toolbox (Delorme and Makeig, 2004 (link)). The EEG data for each electrode were down-sampled to 250 Hz and re-referenced to the grand averages. The signal was then passed through a 0.01- to 30-Hz band-pass filter. Time windows of 200 ms before and 700 ms after the onset of the picture were segmented. EOG artifacts were corrected using an independent component analysis (ICA) (Jung et al., 2001 (link)) (