Visually detectable facial mimicry in response to android facial expressions

Facial mimicry plays a crucial role in human communication. Previous studies have reported that observing human facial expressions induced spontaneous facial mimicry using facial electromyography (EMG) and video data. A previous study reported that the expressions of an android also elicited such mimicry, as reflected in EMG recordings. However, whether such android-induced mimicry could be visually detectable remains unknown. To investigate this issue, we showed dynamic facial expressions of anger and happiness from the android Nikola via a prompter system to participants. We recorded the EMG of their corrugator supercilii and zygomatic major and videotaped their faces, which were automatically coded for facial actions to evaluate brow lowering and lip-corner pulling actions. Nikola's angry expressions induced stronger corrugator supercilii activity in the EMG and brow lowering in the video data, while happy expressions induced stronger zygomatic major activity and lip corner pulling. These results imply that the facial expressions of humanlike androids can induce visually detectable spontaneous facial mimicry in humans, which could be further utilized to coordinate human-robot interactions.