LipIO: Enabling Lips as both Input and Output Surface

Abstract. We engineered LipIO, a novel device enabling the lips to be used simultaneously as an input and output surface. LipIO comprises two overlapping flexible electrode arrays: an outward-facing array for capacitive touch and a lip-facing array for electrotactile stimulation. While wearing LipIO, users feel the interface's state via lip stimulation and respond by touching their lip with their tongue or opposing lip. More importantly, LipIO provides co-located tactile feedback that allows users to feel where in the lip they are touching—this is key to enabling eyes- and hands-free interactions. Our three studies verified participants perceived electrotactile output on their lips and subsequently touched the target location with their tongue with an average accuracy of 93%, while wearing LipIO with five I/O electrodes with co-located feedback. Finally, we demonstrate the potential of LipIO in four exemplary applications that illustrate how it enables new types of eyes- and hands-free micro-interactions.