Experimental protocol and EEG sensor layout.

(a) Events in each trial: a two-second blank window, a two-second fixation, and a two-second cue for finger movements. (b) Illustration of potentials difference during individual finger movements (no data in blank windows). (c) Illustration of a 128-channel EEG sensor layout with 50 electrodes (in red) as the mostly used channel set for decoding.