When exposed to a virtual reality (VR) environment, some users display a type of motion sickness called virtual reality sickness. And it is as real as it is unpleasant! Virtual reality sickness is not limited only to VR displayed using a headset but can occur in other virtual environments, too, such as a mobile platform.
Just like with other types of motion sickness, people experience the following symptoms when immersed in a virtual reality environment: balance problems, nausea, sweating, vertigo, eye strain and headache, disorientation, and even a change in skin color (which is a warning sign).
The Importance of Safety Precautions and Notices
Because of the severity of some VR sickness symptoms, it is important to inform participants of safety precautions and to warn them about preexisting conditions that might trigger discomfort. Standard notices include:
- Warning participants not to stand up too quickly after a session, because some people might experience mild dizziness after a VR experience.
- If an individual is suffering from an ear infection, exhaustion or lack of sleep, it is not advisable to participate in any form of VR.
- If users display any signs of sickness, they should stop immediately. Prolonged exposure will not improve their well-being. It is not physically possible to “power through it”; the longer they play, the more ill they will become.
Degrees of Discomfort
Experience has shown that around one to two individuals in a group of 10 typically suffer an adverse reaction to a virtual reality environment. The likelihood of such a reaction decreases with exposure to virtual reality (practice makes perfect), as the individual’s senses become accustomed to the VR environment. It is important to inform participants of safety precautions.
The adverse reaction is largely dependent on the hardware and software used for the experience. It is also important to note that the more familiar the individual is with the actual experience “in real life,” the more sick he or she may become in a VR environment. Older people are also more susceptible.
Causes of Motion Sickness in the VR Environment
Being immersed in a virtual reality experience causes users to experience several cue conflicts. Their vision expects one input but receives another. A good example is walking in virtual reality; the user feels like he or she is walking but is standing still.
A VR experience can create postural instability, because the information needed to balance is missing or incorrect. Any sense of feeling unbalanced can cause the body to react through nausea and, in severe cases, vomiting.
Some experiences cause an even more severe reaction because of any of the following reasons:
- The VR screen is too close to the eyes (a hardware issue).
- Motion in the periphery (a software or design issue).
- Latency (a hardware issue).
- Unnecessary screen/head movement ( a software or design issue).
Designing for the Mitigation and Prevention of VR Sickness
The design of the virtual reality experience can address and mitigate VR sickness. Here are some things to look out for:
Hardware and Software Considerations
Refresh Rate
A consistent high frame rate (at or above the display refresh rate, or 90 frames per second) is important. Low frame rates and frame dips will cause nausea. It may be necessary to optimize some scenes to provide this consistent rate.
Headset
Whenever possible, opt for the latest headset available.
Latency
Latency (the time between movement and when the movement is visible to the user) should be as low as possible. Latency below 20 milliseconds can enable the use of predictive tracking, while latency above 60 milliseconds can cause nausea due to tracking and distortion.
Flicker/Motion Blur
Look for VR experiences that avoid flicker and motion blur, especially in the user’s peripheral vision.
Design Considerations
Movement
Users should be able to remain seated when possible. In addition, it’s important to assist users by providing arrows to indicate the direction they need to look in, with a limited amount of movement required. If possible, they should be able to avoid excessive head movement.
If the experience requires users to reach for objects, those objects should be within their reach. The VR experience should also limit or avoid uncontrolled movement.
Be sure the experience doesn’t create a mismatch between real and virtual movements. It should only require movements that are appropriate to the experience and that match users’ sensory expectations. Heads should move like heads, and people should move like people. Including breaks from movement will give users time to rest.
Where possible, VR experiences should avoid the following movements:
- Rapid tilting, rolling and bouncing of objects.
- Tilting, spinning or flipping from the user’s viewpoint.
- Sideward movements and movements perpendicular to the direction of the user’s field of view.
- Movements in which physical sensations do not match the visual stimuli.
Transitions
VR experiences should avoid rapid and unexpected screen transitions; they are more effective with short checkpoints that transition the user from one scene to the next.
Visual Elements
To avoid nausea, VR experiences should have a stable focus point or background for users to lock their eye on. Vehicles can help provide reference points in a fast-paced experience.
If the experience requires an elevator, part of the elevator should always be visible so that the users will not feel like they are floating. In addition, reducing the field of view will help to minimize the amount of information the user needs to process. VR experiences should always apply real-world physics to the virtual world; for example, users should not be able to walk through walls.
Throughout the experience, scenes should be realistically lit and not too bright. Furthermore, zooming in can cause nausea, so throughout the experience, camera height and object closeness should be consistent.
Acceleration
The experience should limit abrupt and sudden as well as long and slow changes in acceleration. Acceleration should match user expectations, and a constant speed across the experience might be most comfortable.
Sound
Participants in immersive learning use all of their senses, so it is critical that relevant sounds are included in a VR experience to match the user’s sense of movement.
By considering the design principles in this article, you can offer a VR experience that’s relatively free of VR sickness. Focus on these areas:
- Using the latest hardware, check the refresh rate and latency.
- Ensure that all movement is experience-appropriate.
- Allow acceleration only at a constant speed.
- Create some rest stops along the way.
- Add sound as appropriate.
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