Key Takeaways
- Many VR applications assume a standard range of motion, creating accessibility barriers for users with mobility limitations.
- Using motion primitives—geometric representations of movement—enables customizable remapping of physical motions to virtual interactions.
- Allowing users to customize and remap their physical motion can reduce physical effort and improve usability.
Abstract
Movement-based spatial interaction in VR can present significant challenges for people with limited mobility, particularly due to the mismatch between the upper body motion a VR app requires and the user's capabilities. We describe MotionBlocks, an approach which enables 3D spatial input with smaller motions or simpler input devices using modular geometric motion remapping. A formative study identifies common accessibility issues within VR motion design, and informs a design language of VR motions that fall within simple geometric primitives. These 3D primitives enable collapsing spatial or non-spatial input into a normalized input vector, which is then expanded into a second 3D primitive representing larger, more complex 3D motions. An evaluation with people with mobility limitations found that using geometric primitives for highly customized upper body input remapping reduced physical workload, temporal workload, and perceived effort.
Formative Study
In our formative study, we worked with 10 people with mobility limitations to understand the challenges they face in VR. We had them try different VR applications and observed how the experience worked—or didn’t work—for them. It quickly became clear that many VR games and experiences assume a standard range of motion that not everyone has. Simple actions like reaching for a menu, dodging obstacles, or even just holding a controller could be frustrating or impossible. These challenges highlighted a major gap in VR accessibility and the need for customizable ways to adapt controls to different abilities.
Key challenges included:
- Reaching and large arm movements – Many users couldn’t comfortably extend their arms or make wide gestures.
- Balance and body movement – Dodging, crouching, and leaning were difficult, especially for seated users.
- Two-handed interactions – Some struggled with games that required both hands or precise grip strength.
- Controller and button use – Limited dexterity made pressing buttons or holding controllers uncomfortable.
- Headset fit and setup time – Adjusting the headset and getting started took extra effort for many users.
These findings made it clear that for VR to be truly inclusive, it needs more flexible input options that adapt to each user’s abilities.
MotionBlocks
Based on what we learned, we developed MotionBlocks, a system that makes VR more accessible by adapting controls to each user’s abilities. Instead of forcing users to conform to a fixed way of moving, MotionBlocks allows them to customize how their real-world movements translate into VR.
Motion Primitives
Based on the movements participants wanted to make in the formative study, we created a set of motion primitives—simple geometric shapes that represent different types of motion. These primitives can be combined and customized to create a wide range of interactions.
We found six motion primitives that covered the range of motions users wanted to make:
- Line – 1-dimensional translation toward an object.
- Arc – 1-dimensional rotation around a central point.
- Point – 2-dimensional rotation, without translation.
- Plane – Bounded 2-dimensional translation.
- Hemisphere – 2D rotation around a central point and a given radius.
- Sphere – 3D translation from a starting position.
How Motion Remapping Works
MotionBlocks transforms physical movements into virtual actions by mapping motion between control space (where the user can comfortably move) and transfer space (the range of motion required by the application).
Control-space motion primitives produce a normalized input vector that represents a given movement. This input vector is then expanded by the transfer-space motion primitive into the larger input the application expevts. Using an input vector allows any small, comfortable motion to be amplified or adjusted to match the application's expected input. For example, a user’s small hand motion along a plane near their lap can be mapped to a large swiping action in a hemisphere in VR, reducing physical strain while maintaining full functionality.
Additionally, because the input vector is standardized, it enables flexible remapping across different interaction types. Users can replace spatial motions with alternative inputs, such as using a joystick to control a hand movement or a mouse to simulate head rotations. This modular design makes VR interaction more accessible and customizable to individual needs.
General overview of how the system works. In addition to remapping movement spaces, the modular design also enables the use of traditional input devices like joysticks and mice instead of a transfer-space motion primitive.
User Study
To see how MotionBlocks improves VR accessibility, we conducted a user study with 8 participants from our formative study. Each participant configured their own motion remapping setup using motion primitives and tested it across different VR applications. We compared their performance and experience with and without MotionBlocks enabled.
Key qualitative findings from the experiment:
- Reduced Physical Effort – MotionBlocks significantly lowered physical strain, making VR interactions more comfortable.
- Increased Reach and Precision – Users could perform actions like grabbing objects or selecting menus more easily by mapping small movements to larger virtual actions.
- Better Head and Body Movement – Remapping allowed users to lean, dodge, and look around with less effort, improving gameplay and navigation.
- One-Handed Usability – Participants who struggled with two-handed interactions successfully played games using one hand and a joystick.
- Adaptability Across Applications – Users customized their motion settings for each game, showing that MotionBlocks works across different VR experiences.
Examples of control-space motion primitive configurations. (a) Point primitives tracking 2D wrist rotation; (b) Plane primitives tracking 2D translation forward and sideways across the user's lap; (c) Sphere primitives tracking smaller, more comfortable 3D movements of the head and hands; (d) A Sphere primitive tracking motion in the right hand, mapped to a transfer-space primitive as normal, but additionally the joystick in the right controller provides input to a transfer-space Hemisphere (orange) for the left hand, enabling two-handed input.
NASA-TLX Results
We used the NASA-TLX to get more information about how MotionBlocks affected participants' VR experience. After using VR with and without MotionBlocks, participants rated their experience across six categories: Mental Demand, Physical Demand, Temporal Demand, Performance, Effort, and Frustration.
Key results from the NASA-TLX analysis:
- Lower Physical Demand – MotionBlocks significantly reduced physical strain, making interactions less tiring.
- Less Temporal Pressure – Users felt less rushed and more in control of their actions.
- Reduced Effort – Participants found VR tasks easier to complete with customized motion mappings.
- Consistent Performance – Despite changing their input method, users maintained accuracy and effectiveness.
- No Increase in Mental Load – Even with new interaction techniques, users didn’t feel overwhelmed or confused.
These results show that MotionBlocks made VR more accessible without adding cognitive strain, proving that customizable motion remapping can improve usability, comfort, and overall experience for people with mobility limitations.
Contact Us
Questions? Feel free to contact:
- Johann Wentzel (PhD graduate, University of Waterloo)
hello [at] johannwentzel.ca - Alessandra Luz (PhD candidate, University of Waterloo)
alessandra.luzlam [at] uwaterloo.ca - Martez Mott (Microsoft Research)
martez.mott [at] microsoft.com - Daniel Vogel (University of Waterloo)
dvogel [at] uwaterloo.ca