Fig. 2.

Experiment 1 and Experiment 2. A The experiment of extracting EEG characteristic parameters. All subjects were asked to close their eyes for 5 min to collect the EEG data for analyses. The subjects should wear EEG caps correctly and ensure the quality of EEG signals. During the experiment, the subjects were instructed to stay relaxed without thinking of anything particular and without sleeping, and try to avoid unnecessary movements. All subjects were asked to refrain from using drugs or foods that additionally promote or suppress brain activity since 24 h prior to the experiment. The subjects could clearly understand the experimental process. B The experiment of motor image and rest. Before the experiment started, we explained the steps of the experiment and the matters needing attention in detail to each participant. The subjects were correctly wearing an EEG cap and were instructed to minimize unnecessary movements to ensure the quality of EEG signals. When the experiment started, the first is 12 s of preparation time. Then two stimuli (rest or image, lasting for 15 s respectively) were randomly presented. Participants were required to rest or imagine their legs’ movements according to the corresponding cue stimuli. The interval of cue stimulus is 1 ~ 4 s randomly. EEG data were collected throughout the experiment