Fig. 4

Average power density spectra of EEG signals from the eight selected electrodes (“P7”, “P3”, “Pz”, “P4”, “P8”, “O1”, “Oz” and “O2”) in all trials of Run 1 (left panels), Run 2 (middle panels) and Run 3 (right panels) for five patients (VS2, VS4, MCS1, EMCS1 and EMCS2) and a healthy control. The red and green points indicate flickering frequencies of the target and non-target buttons, respectively. The target frequencies of 6 Hz and 7.5 Hz imply that the target buttons appeared on the left and right sides of the GUI, respectively