Facial expressions, even at their most subtle, cover a wide palette of emotions. The study of these expressions can be approached several ways, including via a camera and facial mapping using FaceReader expression analysis software—but another common method for acquiring this type of data is through facial electromyography (fEMG).
fEMG is a relatively simple procedure that focuses on recording the activity of two specific sets of facial muscles:
- zygomaticus major (cheek muscle used for smiling)
- corrugator supercilli (forehead muscle associated with frowning and negative emotions such as anger, fear, and disgust).
While parsing a subject’s nuanced emotional state can be tricky, zygomaticus and corrugator muscle activity are highly reliable indicators of the physiological components of smiling or frowning. Even tiny variations of expression barely discernible in video are detectable via fEMG, as the slightest tension and release of the zygomaticus or corrugator muscles will be reflected in separate channels in the fEMG data.
So, how do we acquire good quality fEMG?
Since the zygomaticus and corrugator muscles on each side work in tandem during natural smiling or frowning, it’s only necessary to apply electrodes to one side of the face. It’s also important that one—and only one—ground electrode be used; for fEMG, ground is normally applied near the corrugator electrodes.
- First, the facial skin needs to be properly prepared by gently cleaning with an alcohol wipe, after which it’s recommended to apply a skin prep solution called ELPREP to enhance signal quality.
- Next, a conductive gel is applied to the participant’s cheek and forehead.
- Select and apply reusable (EL254, EL654) or disposable (EL513) electrodes.
- Connect the appropriate lead to the selected amplifier. The type of recommended electrode leads will depend on whether the setup uses
- Before recording fEMG data, it’s also highly recommended to verify that the impedance of the attached electrodes falls between between 5 and 10 KOhms. This is easily achieved through the use of an electrode impedance checker called an EL-CHECK, which takes the guesswork out of proper electrode adhesion.
With the proper setup and equipment, acquiring great fEMG data is as easy as smiling.
To learn more, we invite you to visit our webinar page for these and other free, on-demand webinars that detail methods for recording and analysis of fEMG data:
BIOPAC offers a wide array of wired and wireless equipment that can be used in your research. To find more information on solutions for recording and analyzing signals such as ECG, heart rate, respiration and more using any platforms mentioned in this blog post, you can visit the individual application pages on the BIOPAC website.