Procedure

Participants were tested individually in a quiet laboratory at the University of Bath with the experimenter present. Written informed consent was obtained prior to study participation. Participants were seated approximately 60 cm from the PC monitor (17”) with a screen resolution of 1024 × 768 pixel, matching the resolution of the ADFES-BIV⁴³ videos. The faces thus appeared approximately life-sized to the participants, similar to face-to-face conversations. Participants’ faces were cleaned with alcohol swabs to remove any oil or make-up from the face to help secure electrode attachment of the double-stick adhesive rings to the skin. The 10 facial EMG electrodes were then placed in pairs over the respective muscle sites on the left side of the face according to the guidelines by Fridlund and Cacioppo⁴⁸. The electrodes of each pair were placed in close proximity to each other with a distance of approximately 1 cm between the electrode centres. The lower electrode on the lateral frontalis was placed in line with the pupil of the eye when looking straight ahead approximately 1 cm above the eyebrow, and the second electrode was placed just above. For the corrugator supercilii, one electrode was placed directly above the eyebrow lined up with the inner commissure of the eye fissure, and the other electrode was placed lateral and slightly above the first one above the eyebrow. For assessment of the levator labii, one electrode was placed lateral to the baseline of the nostril, and one electrode right below and slightly lateral of the first one. To assess zygomaticus major activity, one electrode was placed in between the corner of the mouth and the bony dimple next to the ear, and one electrode toward the mouth on the same imaginary line. The first electrode on the depressor anguli oris was placed about 1 cm below the corner of the mouth and the second was placed below the first one. Participants were kept blind about the true purpose of the study of assessing their facial muscle activity when watching others’ facial emotion. Thus, participants were told that the electrodes would be measuring pulse and sweat response to facial emotional expressions akin to Dimberg¹. Participants were further asked to sit still for optimal assessment of their body’s responses.

The task started with a short neutral-content clip (4 min 18 sec), which was included to induce a similar neutral affective state in all participants to begin the experiment⁴³. Participants then underwent the facial mimicry task reported in this manuscript (see section Facial Mimicry Task), followed by a facial emotion recognition task which is presented elsewhere⁴⁶. After completion of the computer-task, participants were debriefed and compensated with either course credit or GBP 7.