Simulator sickness of VR 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.
- Disorientation - ataxia, sense of disrupted balance
- Nausea - caused by vection, illusory perception of self-motion
- Eye strain
- 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
- Each individual has difference tolerance of simulator sickness.
How to Avoid
- 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.
- 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.
- 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.
- 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.
- Avoid sudden changes in brightness such as going from a dark room to sunny outdoors.
- 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
- Creating environments where there is a visual horizon will work especially well. You need some visual cue that not everything is moving to reduce the incidence of nausea. A STABLE horizon that the player can focus on while movement is taking place helps decrease nausea.
- See also: Locomotion
- Reduce non-forward movements - Avoid movements that we do not do in real life like looking to the side while moving forward. The solution is to only allowing the user to walk toward where they are facing. While this reduces simulator sickness, it limits the game play.
- Reduce vection - A lot of vection can make some users sick. Effective way to reduce vection is to use simple textures or reduce the speed of the player's movement.
- Reduce accelerations - Because our vestibular system only detects accelerations (changes in velocity) not constant velocity. If the user is moving at constant speed or straight line, they will feel very little simulator sickness from accelerations. Try to avoid frequently slowing down or speeding up and elliptical motions such as turns and jumps.
- Reduce camera yaw - Camera yaw is slowing turning your field of view to the left or right. If the camera yaw control is connected to a stick on the controller or a mouse and keyboard instead of your head motion, you can become sick from vestibular disconnect. Easy way to fix this is requiring the user to stand or use a swivel chair. Additionally, comfort modes can be added to allow users to instantly turn a large number of degrees.
- Add a static reference frame - By adding a static reference frame such as a cockpit or helmet, you can not only reduce simulator sickness but also increase immersion. Users feel the weight of the HMD and subconsciously associate the weight to the virtual helmet in game. This does not apply to all games.
- When the player is in motion, create a black border around the view able area. In essence you are making the viewable area a monitor Temporarily. One could adjust the size of the border, ranging from no border to making it appear as though you are looking at the game world through a window. Players can adjust the size of borders as they gain their VR legs.
- The player must have something in their home that is stable for them to hold onto while experiencing motion in VR. A solid table, a door frame, a support beam in the house. The idea here is to hold it with your hand, and gain the proprioception that the item is NOT moving, despite what your vision is telling you.
- Begin with seated experiences. Build up to artificial locomotion. First try something with a cockpit/car around you for artificial locomotion. The cockpit gives you a frame of reference to not get sick. (like how keeping an eye on the horizon can help against motion nausea in the car)
- At the slightest hint of nausea close your eyes and keep closed until it passes or take of the HMD. Stop playing if it happens again. For real. Stop.
- Never push through nausea. There's multiple reports of people being sick for the rest of day after trying that. We're talking lie down and having to hurl every now and then kinda sick.