Experimental protocol. Each subject stood in the Gait-Assistance Robot (GAR) with closed eyes for 30 s and then with open eyes for 30 s. Subsequently, robot-assisted gait training (RAGT) proceeded for 6 min. Sine-wave sound stimulation (SS), verbal sound stimulation (VS), and no sound stimulation (NS) were provided at 4 min (ST1), 4 min 20 s (ST2), 4 min 40 s (ST3), and 5 min (ST4) after the start of RAGT. Electroencephalography (EEG) were recorded throughout the experimental protocol, and each 4-s segment of EEG data (arrow, ↑) was extracted from filtered data during the 8 experimental periods: middle of the eyes-closed condition; middle of the eyes-open condition; beginning of RAGT (baseline); immediately before ST1; immediately after ST1, ST2, ST3, and ST4. ▼ST1–ST4: first-fourth 2-s sound stimulation. ↑: 4-s segments of EEG data.