Difference between revisions of "Simulator sickness"

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Revision as of 20:21, 2 December 2015

Simulator Sickness is a type of visually induced motion sickness that occurs when using VR and AR devices. The symptoms of simulator sickness include dizziness, headache, nausea, vomiting and other discomforts. Simulator Sickness occurs when the VR devices fails to completely fool our vestibular and proprioceptive systems, the sensory systems responsible for balance, spatial orientation and bodily positions. It is caused by the discrepancies between the motion perceived from the screen of HMD and the actual motion of the user's head and body. In other words simulator sickness from VR is developed when what our eyes see does not match how our heads move. Even minute discrepancy can cause these unpleasant sensations. Simulator sickness is one of the major problems to the wide adoption of Virtual Reality. As hardware and software improve, VR Devices hope to reduce and eventually eliminate simulator sickness.

Gabe Newell from Valve has claimed that its HTC Vive, unveiled in GDC 2015, is the first VR Device that has eliminated simulator sickness from its users. HTC Vive has Lighthouse Motion Tracking system that utilizes lasers to improve the accuracy of the head tracking to under 1/10 of a degree.

Symptoms

  • Disorientation - ataxia, sense of disrupted balance[1]
  • Nausea - caused by vection, illusory perception of self-motion
  • Eye strain

Causes

  • Large and frequent acceleration
  • Loss of head tracking
  • Lack of control from user
  • Using HMDs for prolonged period of time without breaks
  • Low altitude or filling FOV with ground
  • Some users find certain stereoscopic images uncomfortable
  • Wide display field of view
  • High latency
  • Follow Oculus SDK's guidelines for distortion correction
  • Flickering or flashing images rapidly
  • Lack of VR experience[2]
  • Each individual has difference tolerance of simulator sickness.[3]

How to Avoid

Developers

  • Avoid large acceleration and deceleration (linear or angular), especially if the acceleration occurs frequently or over a prolonged period of time. Use constant velocity if needed.
  • Always maintain head tracking. Never stop head tracking even for a short period of time.
  • Avoid unexpected camera movements outside of the users' control. During cutscenes avoid moving the forcing the user to move his or her gaze. Instead, provide examples or suggestions to allow the user to look at the intended target him or herself. Foreshadowing and guiding impending camera movements can help alleviate simulator sickness.
  • Allow or suggest users to take periodic breaks.
  • Height of user's point of view matters. The lower a user's POV is, the faster ground plane changes and fills the user's FOV. It creates a more intense visual flow and can cause discomfort similar to moving up stairs.
  • Stereoscopic images can cause discomfort in certain individuals. Studies have shown that this can be reduced by reducing the disparity between the images. Additionally, any scaling of the IPD should be applied to the entire head model. You should set the inter-camera distance in the Rift to the user’s IPD from the config tool.[4]
  • Wide display field of view can cause simulator sickness. Humans are more sensitive to the motion and imageries in the periphery. Optic flow and subtle flicker in peripheral regions can have a greater effect. Larger FOV also means greater overall visual input which can cause greater vestibular and proprioceptive conflict. Changing camera field of view can lead to unnatural movement of the virtual environment in response to head movements.[4]
  • Make sure your app does not lag or drop frames on systems that meet the minimum system requirements. Minimize Motion-to-photon latency. Any latency between the movement of the user's head and the change of the display of VR device can cause discomfort.
  • Follow the Oculus SDK's guidelines to correct the distortion caused by the lenses. Incorrect distortion correction can appear normal but still cause discomfort.
  • Avoid content with a lot of flickering especially high contrast flashing. Rapid flashing in 1-30Hz range can cause seizure in people with photosensitive epilepsy.
  • Render 2D splash screens in 3D virtual spaces. Minimum of 3DOF of head tracking should be maintained to avoid discomfort.[5]
  • Do not allow the screen to freeze, even for a short time. Fade to black while maintaining audio if needed.
  • If you are creating a seated VR experience, you can place the user in a stationary environment such as virtual chair or cockpit. This can reduce simulator sickness by explaining why they are stationary in real life while moving in VR.[5]
  • Avoid sudden changes in brightness such as going from a dark room to sunny outdoors.

Users

  • More experience you have with VR the less susceptible you are to simulator sickness. Start off with slower and more stable apps. As your body becomes more accustomed to visual and vestibular conflicts, try out faster pace apps.
  • Take breaks between VR sessions.

How to Reduce

Developer

Locomotion

  • Reduce non-forward movements -
  • Reduce vection -
  • Reduce accelerations -
  • Reduce camera yaw -
  • Add a static reference frame -

User

References

  1. https://www.twentymilliseconds.com/pdf/simulator_sickness_questionnaire.pdf
  2. http://www.mitpressjournals.org/doi/abs/10.1162/105474600566952#.VXn0gNIziko
  3. http://www.ncbi.nlm.nih.gov/pubmed/14702999
  4. 4.0 4.1 https://developer.oculus.com/documentation/intro-vr/latest/concepts/bp_app_simulator_sickness/
  5. 5.0 5.1 http://www.google.com/design/spec-vr/designing-for-google-cardboard/physiological-considerations.html