Fig 1. Experimental protocol of the multitask EEG experiment with three different motor conditions, namely motor execution (ME), motor imagery (MI), and movement observation (MO).

Each trial of experiment consisted of 1-sec fixation, 3-sec task performance and 3–5 sec (4-sec on average) resting periods. During the 3-sec task performance, the participants were requested to either physically clench their left hand once, imagine clenching their left hand once, or watch a video clip of a human left hand clenching once, during the entire 3-sec duration.