To show the influence of the reference signal on EEG recordings, Fig. 3(C)–(E) shows the PSD for the reference signal, original referential LTD4, and corrected LTD4. One can clearly see the similar high-frequency activity (20–70 Hz) for the reference signal and referential LTD4 in Fig. 3(C) and (D), which is reduced in the corrected LTD4 in Fig. 3(E). This verifies the following: 1) The high-frequency activity (20–70 Hz) in the referential LTD4 comes from artifacts of the reference signal, and 2) high-frequency artifacts are mostly removed in the corrected LTD4.
