Photo credit: nan palmero via Visualhunt / CC BY

Virtual reality (VR) is becoming mainstream or at least getting some major pushes toward becoming mainstream. Billions of dollars are being invested into the VR industry and VR arcades are being built. The price of VR headsets is also becoming cheaper. GearVR is given out free with the purchase of a new Samsung smartphone. All of these are efforts to get VR exposure to as many people as possible.

With more people getting into VR, there have been increasing number of reported cases of motion sickness. Unlike experiencing motion sickness while traveling, motion sickness in VR is different. You cannot simply wait it out or try to endure it because you are ideally immersed in the VR space. If what is happening in the VR space is causing you to feel sick then the only way to overcome it is to remove yourself from VR entirely.

My goal for this post is to go over what are some of the reasons why motion sickness happens in VR.

What Is Motion Sickness?

Motion sickness in simple terms is when there is a disagreement between what you see and what your body is experiencing. For example, when you travel in a car, you perceive yourself as moving, but your body is stationary. Depending on how sensitive you are to motion sickness, you may start to experience some of the symptoms of motion sickness. The common symptoms of motion sickness are dizziness, fatigue, and nausea. If the cause is not resolved, then the sufferer will eventually vomit.

How does this translate to motion sickness in VR? When you are in VR, there are different factors that can create conflicts between what you see, hear, and do. When this happens, it can induce motion sickness for some people.

Some Factors That Cause Motion Sickness

Latency

Latency is the most common culprit for causing motion sickness because both software and hardware contribute to this problem. For example, as you move your head with a VR headset on, there is latency between your position and when that position is drawn to the screens in the headset. In fact, the position that gets render would be outdated by the time the pixels show up on the screens. Because of this problem, a technique known as Asynchronous Timewarp (ATW) is used to fill in the missing frames to reduce judder. Oculus, SteamVR, and PlayStation each uses their own variation of ATW.

Sensory Conflict

When movement in VR occurs without the user’s action, there is a sensory conflict. For example, you are moving forward in VR space, but sitting down in reality. This will likely cause motion sickness for the person in VR. Depending on how fast they are moving in VR space, the severity of motion sickness will increase.

Eye Strain

The VR headset needs to be calibrated for your eyes. The distance of the lenses from your eyes is one adjustment you can make. Another adjustment is the interpupillary distance (IPD) of the lenses, which is the distance from one eye’s pupil to the other.

When your headset is calibrated for your eyes, you will notice that everything is more clear and crisp. As a result, it can lessen the likelihood of motion sickness.

Why Do Some People Experience Motion Sickness?

Based on a new study, Thomas Stoffregen, a kinesiologist who has been studying motion sickness for decades, lead a team to test the susceptibility of a group of 18 male and female undergraduates during two VR games using the Oculus Rift DK2. The first game involves head movements to roll a virtual marble through a maze. This made 22 percent of the players feel sick after 15 minutes. The second game is a horror game, which uses a gamepad to navigate through a creepy building. This game made 56 percent of the players feel sick within 15 minutes.

What is unique about this study is that among those that felt sick roughly 78 percent were women. This meant out of 18 women, 14 of them experienced motion sickness.

The widely accepted theory behind motion sickness, which is a mismatch between the motion your body is sensing and what your eyes are seeing does not explain the gender gap. Stoffregen believes things that disrupt your balance instead cause motion sickness. Men and women are typically different shapes and sizes so they will have differences in the subtle, subconscious movements that keep their bodies balanced.

To test out the theory, Stoffregen conducted a new study where he measured participant’s balancing motions before they played the games. As a result, he found a measurable difference in sway between those who reported feeling sick and those who did not.

Stoffregen’s finding suggests that gender and age may affect the likelihood of someone experiencing motion sickness.

I hope this post helps you understand why motion sickness happens in VR. If you found this post helpful, share it with others so they can benefit from it.

If you have any questions or believe something else should be added to the post let me know. Feel free to leave a comment, send me a tweet, or send me an email at steven@brightdevelopers.com. I will be glad to hear from you.

If you are a VR developer or someone that suffers from motion sickness in VR then my other posts about tips for developing motion sickness free VR experiences and tips to prevent motion sickness in VR might help you.

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