EEG Preprocessing

The EEG data were bandpass filtered between 3 and 45 Hz using a two-way finite impulse response (FIR) filter (the “eegfilt” function in EEGLAB). High-voltage stimulation artifacts during EVS2 and EVS3 were removed using the digital filters. The artifacts during EVS1 were removed using a quadrature-IVA method (Lee et al., 2019). Data were then re-referenced to the average reference (linked earlobe) and ocular artifacts (EOG) were corrected based on cross-correlation with the reference EOG channels using the AAR toolbox included in EEGLAB. The cleaned EEG data were bandpass filtered into four conventional EEG frequency bands (Groppe et al., 2013): theta (4–8 Hz), alpha (8–13 Hz), beta (13–30 Hz), and gamma (30–45 Hz). The bandpass-filtered data were then segmented into non-overlapping epochs. Epoch sizes were determined such that the epochs include around four cycles at a center frequency of the selected bandwidth (Martin and Schröder, 2016), resulting in epoch sizes of 600, 400, 200, and 100 ms for the theta, alpha, beta, and gamma bands.