InterFACE: Establishing a Facial Action Unit Input Vocabulary for Hands-Free Extended Reality Interactions, From VR Gaming to AR Web Browsing

Extended Reality (XR) interactions often rely on spatial hand or controller inputs - necessitating dexterous wrist, hand and finger movements including pressing virtual buttons, pinching to select, and performing hand gestures. However, there are scenarios where such dependencies may render XR devices and apps inaccessible to users - from situational/temporary impairments such as encumbrance, to physical motor impairments. In this paper, we contribute to a growing literature considering facial input as an alternative. In a user study (N=20) we systematically evaluate the usability of 53 Facial Action Units in VR, deriving a set of optimal (comfort, effort, performance) FAUs for interaction. We then use these facial inputs to drive and evaluate (N=10) two demonstrator apps: VR locomotion, and AR web browsing, showcasing how close facial interaction can get to existing baselines, and demonstrating that FAUs offer a viable, generalizable input modality for XR devices.