We've mentioned nausea a few times in this course as one of the problems in VR. In this video, we will discuss what causes nausea in VR, and ways to avoid or reduce this uncomfortable experience. Nausea in VR is also called simulation sickness, which refers to the discomfort induced by simulated environments. It's mainly caused by the conflict between information received in the brain from our vestibular system and our visual system. In this situation, you are physically moving while looking at something relatively still. So your vestibular system tells the brain that you are moving, but your visual system says you are not, and that's what makes you feel sick. With simulation sickness, it's almost the opposite. Say, you're sitting in your living room chair playing a VR car simulation game. You're physically not moving, but because you are immersed in VR, your visual system is convinced that you are. This then causes the conflict between your vestibular and visual systems, which makes you feel very sick. The best way to avoid simulation sickness is to pay attention to how users could navigate in the virtual environment. Physical movements where users use their own body to move around in VR just like they do in real life, tend not to cause much nausea, if any at all. If you don't want to limit user movement by their physical space, you could consider methods such as walk in place or teleporting. The worst method is to directly import the default first person controller used in many games, where users can move around with the keyboard and mouse and a joystick. A lot of my students have done this to me, and I normally have to take the HMD off to avoid destroying the rest of my day after about 30 seconds. There are other factors that contribute to simulation sickness in VR. Because the displays are very close to your eyes, you might experience eye strain. A frame rate below 90 Herse could cause discomfort as could flashing or high contrast images. So these are the things you might want to avoid when building your VR environments. Finally, just as not everyone experiences motion sickness in cars, some people are less prone to simulation sickness than others. Especially if you are a VR developer and have spent quite a lot of time in VR, your brain is probably more used to it. So it's important to remind yourself that your game might feel completely harmless to yourself, but it could make other people feel very sick. And the best way to find out is to test it on typical users your app is designed for.