Virtual reality sickness (VR motion sickness) is the physical discomfort that occurs when an end user's brain receives conflicting signals about self-movement in a digital environment. While the exact number of people who will be affected by VR motion sickness cannot be known in advance, software engineers who develop VR and augmented reality (AR) environments typically assume that 25% of viewers will experience VR motion sickness. This is the same percentage of people who experience motion sickness on an airplane while traveling through low altitude turbulence.
VR sickness is caused by conflicting signals sent to the brain from the person's eyes, inner ear and body tissue sensory receptors. A pronounced feeling of illness typically occurs when the viewer is watching a digital representation of themselves appear to move quickly in a digital environment while the person's physical body remains stationary. Like other types of simulator sickness, the symptoms of VR motion sickness can include nausea, dizziness/lack of balance, drowsiness, warmth, sweating, headaches, disorientation, eye strain and vomiting. Studies have shown that participants in a VR experience can feel ill up to several hours after taking off their VR headsets.
Underlying causes of VR sickness
There are several theories about the root causes of VR motion sickness and differences in how individuals use vision to maintain their balance may be one contributing element. The biggest contributing factor, however, is thought to be caused by the sensory conflicts that send confusing messages to the brain. This is because even though the person’s eyes may say they are walking around a virtual world, their body will tell them that they are actually sitting down and those conflicting sensory signals cause a feeling of illness.
Current research indicates that gender and age may also play an important role in determining who may fall victim to VR motion sickness. For example, woman are more likely to be affected than men. While some researchers believe this is because women lag behind men in the consumption of virtual reality programming, other researchers believe that women are more likely to get sick from VR because they have better peripheral vision than men and require a larger field of view (FOV) to avoid motion sickness. Different ages and stages in life may also determine if a user will be affected by VR sickness. Genetics are also thought to play a role in determining who will be affected by VR motion sickness. If a person’s family exhibits migraines, inner ear conditions, problems with sight, or past experiences with motion sickness, then it is likely the offspring will be genetically predisposed to suffer in the same way.
How VR developers can avoid making end users sick
The first fix software developers can make to avoid giving users VR motion sickness is to adjust the frame per second (FPS) rate to reduce lag time. VR engineers recommend that instead of focusing attention on using more processing power to create a sharper picture, developers should focus on increasing the speed at which each frame refreshes to at least 90 FPS. This speed will help reduce delay or shaking in the images as they pass across the screen.
Sensory conflict can be aggravated by latency. If a VR participant looks to the right while wearing a VR helmet, for example, the screen shifts left to ensure the viewer's digital environment matches their physical actions. While this shift appears to be occurring in real time, it actually occurs in near real-time. While the movement across the screen may seem immediate to the viewer, the lag time still creates a mismatch between what the person's eyes tell them and what their body's tissue sensors are actually experiencing.
Perhaps the best way to avoid VR motion sickness, however, is to test each shot while creating it and expose someone with high sensitivity to frame rates and see how they react. This approach will inform developers if their shots are smooth and clean enough to leave users unaffected. Other proposed fixes include using headsets that are placed further from the user’s face and using mixed reality (MR) instead of virtual reality to provide the viewer with a fixed horizon or visual reference point.
Unlike virtual reality which immerses the end user in a completely digital environment, or augmented reality which layers digital content on top of a physical environment, mixed reality blends digital and real world settings. Digital cinematographers have had good success preventing VR sickness by simply adding a virtual representation of the viewer's nose or hand to the MR screen. Unfortunately, many current VR locomotion solutions have negative outcomes along with the positive. For example, the extremely helpful fix of using mixed reality takes away the immersive experience that VR users are paying for.