Two-In-One: A Design Space for Mapping Unimanual Input into Bimanual Interactions in VR for Users with Limited Movement
Momona Yamagami, Sasa Junuzovic, Mar Gonzalez-Franco, Eyal Ofek, Edward Cutrell, John R. Porter, Andrew D. Wilson, Martez E. Mott · 2022 · ACM Transactions on Accessible Computing · doi:10.1145/3510463
Summary
This paper addresses a significant accessibility barrier in virtual reality: the requirement to use two motion controllers simultaneously for bimanual interactions. Many VR applications assume users can hold and manipulate two controllers, excluding people who have use of only one hand due to stroke, amputation, limb difference, or the need to control a wheelchair. The authors propose Two-In-One, a design space that provides a structured framework for creating accessible one-handed alternatives to two-handed VR interactions. The design space has two dimensions. The first categorizes bimanual VR interactions into four types based on Guiard's Kinematic Chain theory: symmetric in-phase (both hands move synchronously, like lifting a heavy object), symmetric out-of-phase (hands alternate, like climbing a ladder), asymmetric coordinated (one hand stabilizes while the other acts, like using a smartphone), and asymmetric uncoordinated (independent actions, like dual-wielding swords). The second dimension considers whether computer assistance is on or off—whether the system infers the virtual hand's movement or the user directly controls it. The authors surveyed 39 popular VR applications and found that all observed bimanual interactions fit into these four categories, with asymmetric coordinated interactions being most common (48%). They then applied two "lenses" to the design space—a creation lens for developing input techniques and an evaluation lens for predicting tradeoffs.
Key findings
The researchers prototyped three input techniques for symmetric out-of-phase interactions (climbing walls): (1) **Infer Virtual Hand** uses computer assistance to automatically position the second virtual hand based on the controlled hand's movement; (2) **Alternative Input** uses head gaze with raycasting to control the virtual hand; (3) **Mode Switch** allows sequential control of each virtual hand with a single controller. A video elicitation study with 17 participants with various mobility limitations (cerebral palsy, spinal cord injuries, muscular dystrophy, stroke, ALS) revealed complex tradeoffs between user effort and autonomy. Eight participants preferred inferred virtual hand (less effort, more seamless), nine preferred alternative input (more control, novel experience), and two preferred mode switch (full control). Critically, preferences varied based on the interaction context—participants wanted automation for non-essential movements but full control for strategic gameplay. Participants emphasized that inaccessible gaming is frustrating: 11 described games they couldn't play competitively or at all. All but one felt single-controller input would improve VR accessibility. However, participants strongly requested customizable options rather than one-size-fits-all solutions, including button remapping, adjustable movement sensitivity, and the ability to switch between techniques based on context and daily fluctuations in their abilities.
Relevance
This work provides VR developers with a practical framework for implementing accessible alternatives to two-handed interactions. The four-category classification of bimanual interactions enables developers to systematically identify which interactions need alternatives and what properties each technique should leverage. The tension between autonomy and effort has broader implications for accessible design. Computer assistance reduces physical demands but can feel like "cheating" or reduce immersion; full user control preserves agency but increases fatigue. The finding that preferences vary by person, context, and even daily ability fluctuations argues strongly for offering multiple accessibility options rather than single solutions. The design space extends beyond gaming VR to augmented reality (HoloLens), assistive technology (prosthetics and orthotics), and real-world bimanual tasks. The authors note that bimanual interaction challenges exist outside VR as well, and the input techniques suggested here could improve accessibility in physical rehabilitation and daily living activities. For accessibility practitioners, this paper demonstrates how design spaces can structure thinking about accessible alternatives while preserving the core tradeoffs users must navigate.
Tags: virtual reality · VR accessibility · motor impairment · input techniques · bimanual interaction · game accessibility · design space · one-handed interaction
Standards referenced: W3C XR Accessibility User Requirements