EEG data were processed offline using custom MATLAB scripts (MathWorks, MA, USA) and the EEGLAB toolbox (Delorme & Makeig, 2004). The steps are briefly described as follows: (1) The 50 Hz AC line noise artifact was removed using a notch filter; (2) non‐physiological slow drifts in the EEG recordings were removed using a 0.1 Hz high‐pass filter; (3) the filtered EEG data were re‐referenced to the common average; (4) bad channels and bad epochs were manually rejected by experienced operators. The rejected bad channels were then interpolated from the EEG signals of adjacent channels via spherical spline interpolation; (5) eye movement and blink artifacts were removed using independent component analysis (ICA); and (6) the EEG data were re‐referenced to a common average.
