## 4 Materials
A fourth-order Butterworth notch filter (48-52 Hz) was used to remove 50 Hz power-line interference, while an eighth-order Butterworth bandpass filter (0.5-100 Hz) was employed to preserve critical components of the brain signal. No other filters or processing methods were applied during signal acquisition. Figure 1: Electrode placement for EEG/EMG signal recording. At the beginning, each volunteer was exposed to SSVEP stimuli with frequencies ranging from 5 to 30 Hz, and real-time responses were monitored by observing the EEG spectrum at electrode O2. Responses varied among participants--some showed higher amplitudes, others lower. For each individual, the stimulation frequency associated with the strongest SSVEP response was selected based on visual inspection and expert assessment by the experiment supervisor. Each participant completed four recording sessions, with an approximate one-minute break between sessions to allow for rest. The first session (1 min) recorded EEG/EMG signals representing brain activity free of muscle artifacts, with the participant sitting still and focusing on a non-pulsating LED. The second session (1 min) captured EEG/EMG signals in the presence of muscle artifacts (e.g., jaw clenching), with the participant sitting still but without visual stimulation. The third session (1 min) involved exposure to visual stimulation using a pulsating LED. The stimulation frequency had been selected at the beginning of the experiment to elicit the strongest SSVEP response for each participant. The fourth session (1 min) aimed to record SSVEP responses in the presence of muscle artifacts. The participant was instructed to look at a green, pulsating LED (1 cm in diameter, placed 1 m away from the eyes) while clenching their jaw to introduce muscle-related noise into the EEG signal. The experiment consisted of four 1 min sessions designed to isolate or combine SSVEP and EMG-related components. Detailed descriptions of each session, including task instructions and expected artifacts, are provided in Table 1. Figure 2 shows the EEG/EMG signals recorded during jaw clenching (without visual stimulation) for participant S01. The jaw-clenching artifact occurred around 10 s, producing a substantial amplitude increase on every electrode. Notably, these artifacts also propagate to electrodes O1, O2, and Oz. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Session** & **Duration** & **Task Description** & **Participant Instructions** & **Visual Stimulation/Muscle Artifacts** \\ \hline \multirow{3}{*}{1} & \multirow{3}{*}{1 min} & Recording of EEG/EMG signals without muscle artifacts. The participant sat still and focused on a non-pulsating LED. & Please sit still, relax your facial muscles, and look at the steady (non-blinking) LED in front of you. & No/No \\ \hline \multirow{3}{*}{2} & \multirow{3}{*}{1 min} & Recording of EEG/EMG signals with muscle artifacts (e.g., jaw clenching), without visual stimulation. & Please sit still and gently clench (your jaw for about 0.5 s, then relax it. & \\  & & Exposure to a pulsating LED at the frequency previously & Please focus on the blinking LED and remain still, without clenching & Yes/No \\ \cline{1-1} \cline{3-3} \multirow{3}{*}{3} & \multirow{3}{*}{1 min} & Recording of SSVEP response. & Other artifacts. & Please keep looking at the blinking green LED and gently clench your jaw for about 0.5 s, then relax it. & Yes/Yes \\ \cline{1-1} \cline{3-3} \multirow{3}{*}{4} & \multirow{3}{*}{1 min} & Recording of SSVEP signals with simultaneous muscle artifacts (jaw clenching). & Please focus on the blinking LED and remain still, without clenching & Yes/No \\ \cline{1-1} \cline{3-3} \cline