To analyze correlation and phase synchrony between different scalp channels, we filtered the referential and corrected EEGs to the frequency band 1–50 Hz. Correlation and phase synchrony are shown in Fig. 5(B) and (C) for scalp EEG: T7*F7, T7*Cz, T7*Pz, F7*Cz, F7*Pz, and bipolar (F7–T7)*(Cz–Pz). One can see that correlation and phase-synchrony values of the referential EEG are smaller than that of the corrected EEG. This is different from iEEG in Figs. 3(H) and 4(C) where the correlation and phase-synchrony values of the referential iEEG are larger than that of the corrected iEEG. The reason for this phenomenon is that the reference signal has smaller amplitudes than the corrected scalp EEG, as seen in Fig. 3(B). It can be seen that the corrected F7*Pz has greater correlation and phase-synchrony values than the referential F7*Pz and bipolar (F7–T7)*(Cz–Pz). Hence, correlation and phase-synchrony values of the referential or bipolar EEG cannot correctly reflect that of the corrected EEG in some cases and lead to the misinterpretation of EEG. We also note that the correlation and phase-synchrony values for all corrected EEGs decrease
