HeadTurner: Enhancing Viewing Range and Comfort of using Virtual and Mixed-Reality Headsets while Lying Down via Assisted Shoulder and Head Actuation

Research Background and Problem

• Problem or Challenge: The authors identified that when users adopt a supine posture while using virtual reality (VR) or mixed reality (MR) head-mounted devices, the rotation of the shoulders and head is constrained by the supporting surface. This limitation reduces the field of view and decreases the comfort of head rotation. Studies show that compared to a standing posture, the horizontal head rotation range in a supine posture decreases from 261° to 130°, and the vertical rotation range decreases from 172° to 94.9°. Additionally, users in a supine position require significantly greater subjective effort and neck muscle activation to achieve the same rotation angles.
• Significance: As VR/MR devices become increasingly popular, user comfort in various scenarios, such as prolonged viewing, medical therapy, or leisure, has become critical. Existing hardware and software solutions (e.g., virtual viewport rotation or full-body motion support) fail to fully address this issue and may exacerbate VR motion sickness.
• Research Motivation: The motivation for this study is to investigate the constraints of the supine posture and propose an innovative solution that can expand the field of view and enhance comfort without causing additional VR motion sickness.

Solution

• Method or Solution:
  • The authors proposed a device called "HeadTurner," a 2-degree-of-freedom (DoF) platform triggered by the user's active head rotation. The system adjusts the pitch of the bed and the angle of the pillow to accommodate the user's head and shoulder movements, thereby increasing the field of view and enhancing comfort.
• Innovations:
  1. Dual-subsystem design: one pillow subsystem for head guidance, supporting pitch motion; and another tilting subsystem for body assistance, supporting horizontal rotation.
  2. Platform movements are triggered by the user's head rotation, avoiding sensory conflicts and VR motion sickness.
  3. The system utilizes precise real-time data acquisition (e.g., head posture and distance sensing) to provide smooth and stable responses.
• Implementation Steps and Key Technologies:
  1. Use the tracking functionality of the Meta Quest 3 headset to record the user's head movement data, combined with the OptiTrack system for accurate spatial position tracking.
  2. Employ PID control and angular position feedback techniques to drive linear actuators on the platform, enabling pitch adjustments of the pillow and rotation of the body platform.
  3. The system uses Unity software to analyze and transmit control signals in real-time and provides automated calibration functionality.
  4. High safety design features (e.g., speed and acceleration limits) ensure user comfort and safety during operation.

Research Outcomes

• Specific Results:
  • HeadTurner expanded the user's field of view, increasing horizontal rotation by 24% and vertical rotation by 9%.
  • In experimental scenarios (watching videos and playing first-person shooter games), using HeadTurner significantly improved the field of view (e.g., a 12.4% increase in head rotation range during gaming) while reducing subjective effort and muscle load.
  • Subjective feedback indicated that 75% of participants preferred the supine experience with HeadTurner.
• Advantages Over Existing Solutions:
  • Compared to purely software-based or hardware-based solutions, HeadTurner avoids sensory conflicts, significantly reduces physical constraints, and ensures a natural and comfortable VR experience.
  • Compared to existing motion-based rotation solutions (e.g., rotating chairs) that may induce VR motion sickness, HeadTurner is more effective in reducing discomfort and excels in user engagement and immersion.
• Experimental or Evaluation Results:
  • Compared to a regular bed, using HeadTurner for video viewing significantly improved subjective comfort; in FPS gaming, subjective effort decreased by 1.4 points (on a 10-point scale), though the slight improvement in VR motion sickness (FMS score reduced by 0.4 points) did not reach statistical significance.
  • Some users reported enhanced immersion when using HeadTurner, particularly in tactical operations and increased interaction within gaming environments.
• Limitations and Future Directions:
  • Limitations:
    • The system is relatively costly, as the current implementation uses expensive motion capture equipment and platforms.
    • The system's response speed, especially in pillow angle adjustments, needs improvement to adapt to rapidly changing scenarios.
    • The study sample primarily consisted of young participants, lacking representation from older adults or individuals with physical disabilities.
  • Future Directions:
    1. Optimize hardware to reduce implementation costs, such as using built-in gyroscopes in VR devices instead of external tracking systems.
    2. Add active control modes to predict user intent and automatically adjust the device using technologies like eye-tracking.
    3. Expand the system to more scenarios, such as motion-based games, virtual meetings, or even intelligent multifunctional gaming chairs.

Conclusion

HeadTurner offers an innovative solution to address the limitations of the field of view and comfort in a supine posture during VR use. Its user-driven design and practical implementation demonstrate effectiveness across various application scenarios, providing valuable insights for broader simulation applications and assistive device design.