Jun 15 2015

Simulation Sickness

One of my oldest memories is from a cruise my family took when I was five. Toward the end of the trip I started to feel incredibly sick. At one point I had to simply sit down – I was immobilized with nausea and a general feeling of unwell. I am told I later vomited on the captain’s shoes, although I don’t have any memory of this.

What I was experiencing was simple motion sickness. There is a related phenomenon emerging known as simulation sickness. When the CEO of Oculus first used their Oculus Rift virtual reality game system, he experienced symptoms of motion sickness.  It’s a serious problem for this new technology, delaying full deployment.

The problem is rooted in neuroscience. Our brains receive several types of sensory information that tell it about it orientation relative to gravity and any acceleration or motion it is experiencing. The eyes simply see how our head is moving in relation to the rest of the world. Our vestibular system senses both our orientation with respect to gravity and acceleration. It does this through three semicircular canals, a utricle, and a saccule in each inner ear, oriented in each three-dimensional axis. These canals are filled with fluid and lined with tiny hairs projecting from neurons. The semicircular canals experience rotational acceleration, while the utricle and saccule measure the direction of gravity and linear acceleration.

Further, our muscles contain stretch receptors that give feedback to the brain about how they are contracting. Finally there is proprioception, a type of sensation that tells the brain where our limbs are in three-dimensional space. A simple test of proprioception is to close your eyes and then touch your nose.

The cortex and cerebellum take in all this information and compare it in real time. This processing is primarily used to create balance and aid in coordination. The cerebellum does most of the heavy lifting here with contributions from the cortex for voluntary control. Motion sickness is what happens when the various types of sensory input related to position and movement give conflicting information to the brain. These symptoms include vertigo, which is a subjective sense of motion, often spinning. People might simply notice feeling off balance without spinning, and when severe these sensation can result in nausea and vomiting.

Motion sickness specifically refers to a situation in which these symptoms result from the vestibular system sensing motion while the eyes do not. If you are on or in a vehicle that is undergoing significant acceleration but your eyes do not perceive it because the objects immediately around you are stable, that can cause motion sickness.

Simulation sickness is similar but in the opposite direction. Vestibular and proprioceptive input are telling your brain that your body is not moving, but your eyes are telling your brain that it is. There seems to be a threshold effect for this to kick in, and it is likely different with every individual. I have played many video games with screens of various sizes and distances from me. If the screen fills a certain amount of my visual field, then playing action games will produce simulation sickness. Simply moving back from the screen or reducing the size of the game window is all that is needed to avoid feeling sick.

Oculus Rift is a new virtual reality system in which you wear bulky goggles that complete cover your visual field. It is meant to me immersive virtual reality. Further, as you turn your head the computer changes your view, so you can literally look around your virtual world simply by turning your head. This, of course, is a perfect setup for simulation sickness. In fact, it’s hard to imagine how it wouldn’t cause simulation sickness in those who are susceptible.

Gamers are trying to develop and share home remedies for simulation sickness. I doubt any of them are really effective, except one – slowly build up your “resistance” to simulation sickness over time. Use Oculus Rift for a short period of time, stopping when you develop mild symptoms. Do this every day, and hopefully you will be able to go longer and longer before you develop symptoms. Eventually you may be able to use the device without nausea.

This is called “vestibular therapy” and it’s exactly what we do for patients who experience pathological vertigo. There are probably two things happening with this therapy. The first is that the brain gets better at synchronizing the various sensory inputs so that they match better and trigger less vertigo. This mechanism is probably more relevant to vertigo than simulation sickness. The second mechanism is that the brain’s plasticity adapts it to the vertigo so that the symptoms become progressively suppressed. In other words, the brain produces less of the symptoms of vertigo in response to the sensory mismatch.

That is a lot to ask of your customers, however; to slowly build up a tolerance to the nausea produced by using your product. Serious gamers hungry for virtual reality will probably do it, but obviously the industry would love a technical fix. They are working on various options.

One option is eye tracking, which will allow the software to adjust the presented view not only to head movements but to eye movements as well, simulating a real experience more accurately.

One preliminary study found a decrease of 13.5% in the number of players experiencing simulation sickness when a virtual nose was placed for reference in the frame.

VR developers are also trying to improve the video itself, increasing refresh rate, reducing light intensity, and reducing motion blur in the video. Reducing lag is also critical. Even the slightest lag between moving your head and the display tracking accordingly can be sickness-inducing.

Some games are also less prone to simulation sickness than others. For example, flight simulators, where you have a static cockpit for reference, are better than games in which the entire visual field is moving. This is what led to the “virtual nose” idea. We may see games specifically designed to minimize simulation sickness early on, until the technology matures further.

Conclusion

I am highly looking forward to virtual reality gaming (and I have been for literally decades). I am excited that VR gaming is finally here. However, I am also very sensitive to motion sickness and I suspect I will have a hard time adapting to the technology. I am therefore being patient and waiting for the technology to improve and at least make the easy fixes to help minimize simulation sickness. It is likely, however, that I will have to adapt to VR gaming and may have to pick and choose which games I can tolerate.

When the technology matures, and I can afford to buy one, I’ll report back on my experience. Meanwhile it would be great if any readers can report on their own experience in the comments.

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