On VR Development and Avoiding Motion Sickness

November 04, 2016 by Crytek

On VR Development and Avoiding Motion Sickness

You don’t want to have to think about feeling nauseous when you’re playing a video game, and VR devs don’t want you to have to think about it either. But if you’re not careful about how you design a VR experience, it can cause symptoms akin to motion and simulator sickness. So when we’re developing a new VR title, we think about it a lot. So you don’t have to.

If you haven’t trained as a pilot or astronaut, you probably haven’t experienced simulator sickness. But you’re probably familiar with car sickness—i.e. motion sickness—if not personally, then via the experiences of a friend. What happens when you get motion sickness is this: you get in a car (or on a boat, or a plane, or a train). The car begins to move. You can see that your feet are planted firmly on the ground, but at the same time you can see things moving outside of the window. Your brain starts to worry. Am I moving or am I standing still?

This might sound like an easy question, but it can be a very confusing moment for your brain. If you’re lucky, your brain will settle the question quickly, accept that you are sitting still inside of a moving car, and get on with thinking about which game you’re going to buy next. If you’re unlucky, i.e. prone to motion sickness, your brain might settle the question by emptying the contents of your stomach. This isn’t right! Am I hallucinating? your brain thinks. Maybe I’ve been poisoned! Better empty my stomach just in case. This phenomenon is called sensory conflict, and the results are anything but fun.

In slightly more scientific terms, when you experience sensory conflict, your vestibular system is sending your brain messages about what your body is doing that contradict the messages from your eyes. It is referred to as a sickness, but it isn’t a disease. In fact, you need a fully functioning, totally healthy vestibular system in order to experience it (lucky you!), and your body can (and likely will) adapt to the situation causing it in time, which has also led researchers to refer to it as a “phenomenon of maladaption.”

VR sickness originates in sensory conflict as well. Your body, which might be sitting still in a chair or standing in your living room, is sending one message to your brain about what you are doing while your eyes, immersed in a virtual world, are sending another. This conflict can be exacerbated in VR if the frame rate is slower than your brain’s processing power, but a lot of elements can contribute to the effect: flickering light, speed of movement, camera control issues, scaled motion, or as we discussed in Seeing Is Deceiving: Your Brain and VR, first person shooter standards like weapon sway, walking gait, or head bob. This is where game dev wizardry comes in.

“There is a wealth of information about what makes people sick in VR and how to avoid it,” explained Ali Helmy, Animation Programmer at Crytek. “The main problem is: how do we take this information into account and make a game that’s fun? We could create a super nice sitting simulator that does an awesome job of simulating sitting on a chair at a desk and there would be zero nausea, but who would play it?”

No one. That’s who. So it’s a good thing we already know a lot about eliminating VR sickness.

VR Sickness Solutions

Keeping frame rates high and latency low is one of the most obvious solutions to the problem. The higher the frame rate, the more willing the brain is to believe in your virtual reality—and the less likely you are to end up feeling sick. Helmy explained that the max possible frame rate on the VR dev kits has risen with each subsequent kit he’s seen. “Everybody realized very quickly that you need a high frame rate and low latency,” Helmy explained. “You need zero frame delay between your motion and the camera motion. Frame rate is crucial. When it is too low it might not make you nauseous, but it might give you a massive headache.”

Another solution you’ll hear VR devs discussing is camera control. Don’t take camera control away from the player. However, according to Helmy, there are situations in which you can take partial camera control away from the player. Camera rotation is trickier.

“At first we said, that’s it, no camera motion, no camera rotation, do not take control of the camera. However if you look at The Climb you will notice that we do occasionally take camera control. For example, when you reach a ledge you grab onto the side and pull yourself up until you’re standing on top of it. In those moments we’re moving the camera for you. The real issue is whether or not the movement is player initiated or player actuated. So if the player decides to jump, jumps, and then we move the camera for them, they are more likely to be ok with the camera imitating a jumping movement. Your brain expects it and accepts it,” Helmy explained.

It turns out, meeting the brain’s expectations is another big key to getting your brain to believe in a virtual world and avoid nausea and headaches. Dissonance between expectations and experience in virtual reality can yield unpleasant results.

“If you hit something in a racing game you expect to be thrown forward, and if that doesn’t happen your brain is like *makes gagging noise*,” Helmy said. “Your brain is like this computer that is living in this spaceship that is your body. It knows. When you jump certain senses will tell you you’ve landed. But if that never happens, my brain is like, what just happened?” Another sensory conflict.

People have been researching these issues for a long time, but we still have a lot to learn about VR. Crytek’s VR Research and Development team is always testing out new approaches.  

With the right combination of software and hardware solutions, future VR devs might not have to tailor as many development decisions to the VR medium. Julius Carter, Game Designer for VR Research and Development at Crytek, is working on a number of prototypes that address VR sickness issues. “But if I told you about them now, I’d have to kill you,” he joked when I asked him to describe them.

While we know these and other hardware solutions are in the works, for now, developers must solve the VR sickness quandary with elements they can manipulate now: gameplay, locomotion, careful camera work, audio, and graphics.