2.3.3. EEG preprocessing
The EEG preprocessing was based on the procedures described in Kotowski et al. (2023). The code was written in Python 3.9.7 using the MNE 0.24.0 package (Gramfort et al., 2013) and will be publicly available after publication. In short, any manually identified corrupted channel (various individual channels in 17 participants) were interpolated using spherical splines (Perrin et al., 1989). The EEG channels were recalculated to common-average reference and band-pass filtered between 2 and 40 Hz using a third-order zero-phase forward-backward digital Butterworth filter (Gustafsson, 1996). ERP epochs between -100 to 500 ms relative to stimulus onset in correct trials were extracted. Ocular artifacts were corrected by removing independent components (ICs) correlated with eye blinks in EOG signal by more than 2 SD s higher than others. We manually removed some additional artifactual ICs for 16 participants (on average 1.4 ICs per participant, as reported in the code provided above) that were not detected by the algorithm due to weak EOG signals or due to artifacts of non-ocular origin. Finally, the ERPs were corrected with respect to the 100 ms pre-stimulus baseline.