Fig. 2

Power spectrum (top panel), event-related spectral perturbation (middle panel), and the spectral density (bottom panel) of three groups at Oz. The time window interval was [−500ms, 500 ms] with the checkerboard onset at 0 ms, and the frequency band analyzed was 4–30 Hz. Two horizontal lines in the top and middle panel indicate the alpha band (8–13 Hz). Two vertical lines in the spectral density plots indicate the alpha band