Electrophysiological activity was register with a 64-channels EEG system (Biosemi ® ActiveTwo) with electrodes positioned according to the 10-20 international system at a samling rate of 2048 Hz (band-passed 0.1 to 100Hz). Four external electrodes were used to monitor eye movements. Two of them were placed in the outer canthi of the eyes in order to record horizontal EOG and the other two were positioned above and below the right eye to record vertical EOG. Two additional external electrodes were placed on bilateral mastoids for re-referenciation. Data pre-processing was performed using MatLab (The Mathworks, Inc.), EEGLAB (Delorme and Makeig, 2004) and ERPLAB toolbox (Lopez-Calderon and Luck, 2014). The signal will be down-sampled at a rate of 512 Hz and band-passed between 0.1 Hz and 30 Hz for ERP analysis. EEG signal will be segmented into epochs from -500ms to 1200ms respective to stimulus onset. The ERP components under interested in this proposal are P1, N170 and N400. P1 component is traditionally defined as the highest positive voltage observed between 20 and 110 ms after stimulus onset and is generally recorded over occipital region. N170 is commonly identified as the highest negative amplitude value observable around a latency of 130 to 210 ms after stimulus onset and its scalp topography is centered over occipito-temporal. N400, on the other hand, is a monophasic negative deflection that occur around 400ms after the onset of the stimulus and whose topography over the scalp, although more difficult to characterize, seems to be centro-parietal.
2.5. Statistical analysis of ERPs