Quadmetric Optimized Thumb-to-Finger Interaction for Force Assisted One-Handed Text Entry on Mobile Headsets

Abstract

Augmented reality head-worn computers often feature small-sized touch interfaces that complicate interaction with content, provide insufficient space for comfortable text input, and can be awkward to use in social situations. This paper presents a novel one-handed thumb-to-finger text entry solution for augmented reality head-worn computers. We design a glove composed of 12 force-sensitive nodes featuring an ambiguous keyboard layout. We first explore the viability of force disambiguation to evaluate the force division within the force spectrum. We select a 3-level force division as it allows to considerably reduce the number of keys while featuring a high (83.9%) accuracy. Following this pilot study, we map the 26 English characters onto the 9 nodes located on the index, middle and ring fingers in a 3-3-3 configuration, and attribute the space, enter and backspace keys to the remaining three nodes. We consider text entry performance as a quadmetric optimization problem considering the following criteria: goodness of character pairs, layout similarity to the QWERTY keyboard, easiness of force interaction, and comfort level of thumb reach. The resulting layout strikes a balance between performance and usability. We finally evaluate the quadmetric optimized layout over 6 sessions with 12 participants. The participants achieve an average text entry rate of 6.47 WPM with 6.85% error rate in the final session, which is significantly faster than existing thumb-to-finger solutions. In addition, our one-handed text entry system enhances the user mobility compared to other state-of-the-art solutions by freeing one hand, while allowing the user to direct his visual attention to other activities.