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Everything You Wanted to Know About Simulator Sickness

Summary: Almost everyone experiences sickness of some kind. Users may need to re-adapt to every application for the Oculus Rift. Keep sessions short and allow users to control intensity to match their preferences.

Motion sickness has been a pretty common theme in the Oculus Rift forums. The Best Practices Guide is full of tactics you should use in your application to help users avoid motion sickness. People discuss which gaming rigs and graphics cards help get the highest frame rates, the better to avoid motion sickness.

That said, there are a ton of questions people about motion sickness. How common is it? What are the most common symptoms? What makes people more prone to sickness?

US Navy Logo US Navy Seal by US Army Institute Of Heraldry - Keeleysam.
Licensed under Public domain via Wikimedia Commons.

Fortunately there’s an organization that has been doing research on this for decades - the United States Navy. The Navy realized that doing training missions in flight simulators was much cheaper (and less risky) than in its aircraft, so starting in 1960, they began training their pilots in ever-more-advanced simulators. Unfortunately, some of their pilots would get sick, and they worried about how simulator training would carry over to the actual planes, so they commissioned lots of studies to determine what causes motion sickness, how common it is, and whether simulators would help Navy pilots fly planes better. Today we’re going to take a look at the “Introduction to and Review of Simulator Sickness Research”, written by David M. Johnson in 2005.

Can research into Navy simulators actually tell us anything about virtual reality headsets?

Interior of a Navy flight simulator

This is a legitimate question. Navy simulators use hydraulics to change the orientation of the simulator when you do things like turns, and Oculus et al do not. Navy pilots also tend to be young adults, mostly men, and headset users will make up a wider proportion of the population.

That said, the simulators used by the Navy have a very wide horizontal field of view, and the image being simulated is a flight during a cockpit (one of the most common VR demo types to date). From reading the document, it sounds like a lot of the things discovered by the Navy have also been discovered by the VR community.

Let’s get into it!!

General Facts about Simulator Sickness

How common is it?

This tends to be extremely difficult to measure, and varies widely across individuals and simulator tasks. Depending on the task and the criteria used for measurement, incidence ranged from 10% to 90% of users who got motion sick. Here are the incidences of sickness from five different studies of five different simulators:

In one study, 61% of those sick had their symptoms persist between 15 minutes and six hours. Symptoms very rarely persisted the morning after a simulator session.

What things make you more prone to motion sickness?

Why do we get simulator sickness?

There are a few theories. Most pinpoint the difference between the motion perceived by your eyes and the motion reported by your inner ear. One theory says your brain interprets the sensory mismatch as evidence of having been poisoned, leading to nausea/vomiting.

Animals also get motion sickness.

Motion sickness is generally more correlated with gastrointestinal distress - symptoms like burping, nausea, and vomiting. Simulator sickness is more correlated with visual distress - eye strain, difficulty focusing, disorientation, and headache.

How were these tests conducted?

Generally, by asking pilots after they took turns in the simulator, and then aggregating data about them, or running correlations based on other facts about the people that got sick (age, etc). Some of the other studies about motion sickness date from World War II when a much wider range of people were being transported across the high seas.

Because symptoms vary so widely from person to person, a very large number of pilots are needed to establish statistical significance. This made testing in controlled environments difficult. In studies that had large numbers of subjects, the researchers had less control over the environment or the test conditions. The same testing difficulties will likely apply for user experience researchers. A wide number of subjects will need to be tested to draw conclusions about a given stimulus.

What other things should I know about?

Conclusion

Almost everyone experiences sickness of some kind, depending on the environment, and almost everyone adapts. Because people adapt to simulator conditions, and because symptoms vary widely, you’ll need to test a large number of people to draw conclusions about whether your application causes sickness.

The most common symptoms are dizziness, eye strain, disorientation, and nausea. Actual vomiting is rare.

The Navy had strict conditions about when pilots were allowed in the simulator (as well as a smaller age range than the general public). People are going to try to play your game while drunk, people will play with head colds or the flu, children are going to try your application, even though they are all more susceptible to sickness, and you won’t be able to control it. You can add settings to your game to allow the user to control the intensity of the experience.

When users are just starting with your game, keep sessions short, try to avoid forcing the user to move their head, and put more intense experiences at the end of a session.