Wireless Surface Electromyography Recording of Facial Muscle Activity During Expressions

Begin with a human participant seated before a display screen, wearing an adhesive mask embedded with dry electrodes.

Electrodes are placed over the important facial muscles to non-invasively record surface electromyographic, or sEMG, signals linked to muscle movement.

A wireless unit near the ear collects and transmits these signals.

The participant follows various facial expression videos.

Each expression is held briefly, followed by a rest period, to capture muscle contraction and relaxation.

During an expression, motor neurons within the facial nerve send signals to the facial muscles, causing them to contract.

This generates electrical activity in the muscle fibers, detected at the skin surface as an sEMG signal.

As the muscles relax, these signals decrease.

The muscle contraction during the expressions shows high signal amplitude compared to the resting period, revealing distinct patterns for analyzing facial muscle activity.

To begin, carefully remove the electrode mask from the case and inspect its shape to ensure a proper fit on the face.

Place electrode number 11, marked with an eye symbol, near the participant's right eye. Position electrode number 8, marked with a nose symbol, on the nose. Attach electrodes 13 to 16 on the forehead and then attach 1 to 2 electrodes on the chin. Now place the reference electrode on the right mastoid.

Gently press the mask onto the skin and carefully peel off the outer transparent support films one by one to fully attach the mask. Ensure the mask remains in place throughout the process.

Remove the protective film, insert the electrode array connector card into the DAU's connector socket, and secure the DAU to the tape.

Seat the participant comfortably in an upright chair at a fixed distance, such as 70 centimeters, from the computer screen.

In the electrodes application, select the DAU ID number and click Confirm to pair the tablet and DAU. Choose the electrode mask montage and click Confirm. Now, select the channels to display on the screen with desired filters and click Confirm. After selecting the channels, connect the tablet to the computer using a cable and change the Android tablet USB settings from transferring files to USB tethering. Verify that all 16 electromyography electrode signals are detected in the application on the tablet before proceeding.

Open the tablet’s electrode application and press Start session to begin EMG recording. Enter the session details, including Study name, Session name, Site, Operator, Patient ID, Age, Gender, and Remarks. Then, click Start Recording to capture EMG data.

If calibration is required, the application will prompt the participant to perform basic tasks such as closing eyes or chewing. Click Start to initiate calibration. Once completed, click OK to proceed or click Next to skip. Once the entire calibration is complete, click Done and OK.

On the computer, double-click the experiment file facial_expressions.psychopy. After closing unnecessary pop-up windows, click on Run experiment to launch the protocol. When prompted, enter session details such as participant number, session number, and tablet name, then click OK.

Have the participant perform 11 facial expressions as instructed by the video guide. After holding each expression for five seconds, give a three-second rest.

Once the experiment is complete and PsychoPy automatically stops, click END recording to stop EMG data capture on the tablet. Now, click Yes, stop. After the confirmation window appears, click OK.

Finally, press the Sync button to synchronize session data with the system's cloud and press OK when complete.