How to Prevent Simulator Sickness

October 22, 2023March 29, 2018 by Pablo Farias

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Table of contents

Simulator / VR Sickness

Body sensations don’t match visual stimuli
Sensitivity varies between people
- Must test with A LOT of people
Science / biology is unknown
Trial and error is revealing what works and what doesn’t

Known Triggers

Forcing rotation on the user’s field of view
Mismatch between real and virtual movement (acceleration)
Low frames per second (FPS)
Lag / slow response time to movement
High field of view (FOV)

Locomotion Techniques

No movement
Teleportation
Constant velocity
Vehicle / cabin
Arm swinging
Climbing
Degrees of freedom influence options available!

Further Reading

Transcript

You might have heard about people getting sick when they try virtual reality. It might even happen to you. What we’ll do in this lesson is talk about what’s known as Simulator sickness or, VR Sickness.

Humans have what you could call, an inner accelerometer that can detect rotation and acceleration as well. For example, if you go on a rollercoaster or a swing, or if you spin around, you will feel the acceleration and the rotation even if your eyes are closed. So we can call this an inner accelerometer. This is called the Vestibular system and it passes information on to your brain that is combined with information from your visual system so that you can keep your balance and your posture. So it is a very important system in our bodies, which allows us to stay balanced, not fall out.

So, there are different theories regarding why motion sickness can happen. When you are in a car and you are reading a book, for example, some people will feel nausea. I am one of those people, so I can’t really read when I’m in a car. And what’s happening there is that there is a difference between what my visual system is seeing, which is, would be a book or a phone, and what my vestibular system is experiencing, which would be rotation and acceleration. So, there is a difference. And one of the theories around why motion sickness happens, says that it happens because of that difference when you have that discrepancy between your visual stimuli and your sensory experience.

Now when it comes to virtual reality, the correct term here is not motion sickness, it’s Simulator, or VR sickness, and sometimes you also see it as Induced Motion Sickness, which kind of works the same way. There is basically a discrepancy between what you are seeing and what you’re experiencing. But it’s usually the other way around as in we are seeing movement, for example, and we might not be moving at all.

So again there is, it is unknown, the exact biology and science as to why this happens. There are many theories. But what we do know is that the sensitivity to this issue affects different people in different ways. There are people that have differences in intensity of these problems. And also there are things that make some people sick and other people are not gonna even notice that, or they’re not gonna be affected by that. So, this is a very important aspect for when you are developing virtual reality experiences.

With virtual reality experiences, you can trigger deep sensory experiences in your players which can create incredible, amazing experiences, but it can also turn into something very nasty if the experience makes people sick. So what you’ll want to do early on is test your project in virtual reality, test it yourself as soon as possible. And also test it with as many people as you can because there are things that affect some people and not others so you want to get a really good amount of feedback and testing before you actually launch your game.

So, just as a personal anecdote, I took a bunch of VR mini-games that I made to, like a meet up group on virtual reality and different people tried them and the ones that I thought would make people sick didn’t make anyone sick, but one of them that I didn’t think it would make anyone sick, which is a moving platform, actually made some like people feel a little bit like it was too much. So, you’ll want to get a lot of feedback from different people.

And even though science and biology are behind, we don’t know the extent mechanisms or biology behind these problems, actually the industry is figuring it out by trial and error. So by trial and error developers in the community are starting to learn what works and what doesn’t work. But again this is early days so don’t take any of this as if it is set in stone. You can always try and do different things. But these are some really known triggers that are backed by, that you can easily test as well in a couple of people and one of them will be sick. I get sick actually, with almost all of them, except for the last one.

So, one thing that you should always avoid is forcing rotation on the person’s view. In real life, let’s say you want to look to one direction so you can always move your head and do it. But imagine if you’re trying to look at that direction but some machine is moving your head to the other way that is what happens when you try to rotate the camera of the player inside of your game. So that is something you want to avoid.

Related to that is when there’s a mismatch between what the person is seeing, the movement they are seeing, and the movement they are experiencing. So, if you do want to have people moving in a virtual reality experience, which will be the case in many times, you probably want to avoid or reduce acceleration. Acceleration is a change in speed over time, and that is what we actually experience. Once we are at a constant velocity we don’t really experience anything. So, if you are going to have something that is moving try to make it move at a constant speed, for example. And try to make the start of that movement, maybe a little bit soft so that the acceleration is not felt as much.

Then other things that make you sick are actually things that can have to do with poor performance in your game but also with devices that have poor capabilities. So low frames per second. Frames per second are the amount of images that are rendered per second in your game. When that number drops it’s usually because there’s too much CPU processes going on that can actually make people sick. And that is something that you can easily test, if you try Google Cardboard experiences on phones that are not made for virtual reality you get very low frames per second and it’s absolutely horrible.

Also, when there is lag, so if you move in virtual reality and there is a lag when the world updates after you move your head, so you move your head and you’re still seeing the same thing and then like a second later, or a fraction of a second, the move moves with you. That can also make people sick and that can make you very sick. So, those are things to take in mind.

Then research, at least according to the Oculus website, and some other places that I looked, says that the more- the higher field of view that you have the more sick people tend to be. Field of view is the angle at which you view in virtual reality. So when we’re not wearing a head-mounted display, we can actually see almost 180 degrees. But in a head-mounted display, you usually get a tunnel vision. So depending on the platform there will be different angles and also vertical angles that you will see.

It seems that higher angles usually make people more sick, although, they bring better immersion in the experience. So that’s a bit of a trade-off. Because if you have a head-mounted display with a very small field of view and maybe it will make people less sick but, it can also feel like, at least I feel a little bit claustrophobic if I really can’t see that much to the sides. Some technique people have tried is to have like a cockpit for example, like a plane cockpit where you can see the borders so it kind of reduces your field of view and that seems to have helped some people.

And now something I want to mention as well, related especially to the first items is that 360 video can actually make people quite motion sick. Quite simulator sick. Because in 360 video a lot of the times people are, the camera is just moving all over the place. For example the GoPro 360 videos on YouTube that can be view in Google Cardboard are beautiful videos. They can make a lot of people sick, at least they made me sick when I tried the surfing one and the snowboarding ones. So that is something to keep in mind.

Now, we talked about what doesn’t work but let’s talk now about what works and how people can move in virtual reality. Movement in virtual reality is called- movement is called locomotion, so when we talk about locomotion techniques we are talking about ways in which people can move in a virtual environment. I’m going to mention things, show some examples.

First of all, you can have no movement at all. You can just be in a fixed position. You can look around. And that is going to have a high comfort level for people because there is no acceleration, there is no discrepancy between movement, although, if your head mount display doesn’t have position tracking and you’re standing up and you try to lean forward or lean backwards or you try to jump and you’re not seeing that reflected in virtual reality that can obviously affect comfort. So in general, position tracking is better than no position tracking when it comes to comfort in my opinion, and my experience.

Now, we can also have no movement, but where we are, we are always first person in virtual reality, because we are always there but we could be controlling a character that is in third person. So that is just another example. And we have full control as to where we want to look and we can control the character, with say, a controller. Then, what I mentioned before, when you have position tracking it is more natural, the direction is more natural than when you don’t have position tracking because if you lean forward, you also lean forward in your VR experience so the movement you are seeing in the virtual world matches the movement you are experiencing.

Also the height of your character in virtual reality, in this case, is the same as your height in the real world. Well, clearly not, the scale is different but the distance from the ground feels similar because that is measured when you set up your platform, your headset. So, that also helps.

Then, a very commonly used technique is called teleportation and it consists on using a point, or reticle, or like a laser pointer to point where you want to go and then you are transported instantly to that location. So, that is a way to avoid having to deal with velocity or acceleration, as I mention before, it’s not a a good thing to have. So, if you can avoid having, this is a way to make it more comfortable. Because people move with this teleportation system to a new position and then in that position they can just look around and they are not being accelerated into any direction. Then you can have movement with constant speed.

Like in this example here. And in this example, the player doesn’t really decide where they are going. They can even activate the movement or stop the movement. And, the wait goes from not moving to moving is a bit abrupt so I found that this actually did make some people a little bit like it was too much even though I thought it was really, really comfortable.

Now, what also helps in different experiences is to have these sort of handrails or elements around you that make it, give it a more anchored reality, kind of, kind of sensation so that you’re not, you feel, you don’t feel like you’re just floating in the middle of nowhere, if that is something that could make some people a bit uncomfortable in the experience.

Then there is also the option to have constant speed but in a variable direction. So in this- in this animated GIF here the person actually decides where they want to go by looking at that direction and then they activate movement to that direction. Once they activate movement they are moving on that fixed direction even if they look elsewhere until they activate the movement again by pressing a button.

So, a variation of this that you will encounter in some mobile games is what I call move where you look. It is something similar but say if you look to the right you start moving to the right and then you look to up and you start moving up. That actually makes me personally a little bit sick. I think it’s better if you, if you make it as a fixed option. Now, it is always an alternative to have more than one type of locomotion in a games. You will see some games that offer options to the player. They can have, like free to like teleportation and, for example, using the gamepad to also move. Because some people don’t get sick at all and they will want to be able to explore freely.

Another type of experience of movement in virtual reality is when you are moving in a vehicle; this could an aircraft or a land vehicle. And on a vehicle there are a few things that are important: one of them is that you have elements around you, like I said before. You have like, handrails, in this case you have like couple of buttons and windows and that whole cockpit so that can definitely help.

And then, now in a vehicle it’s very high likely that you will want to turn so that means you’ll have to induce some sort of rotation. And, what people have found is that when it comes to rotation, when you have a smooth rotation it actually makes people more sick than when you have discrete step rotation. This particular case the buttons on the dashboard are used to rotate but each rotation, it’s like a discrete step. It’s not a smooth element. That can also help with motion sickness.

Then, there is now locomotion techniques that requires hand tracked controllers which is arms swinging. And, in this technique you look where you want to go and then you move your arms up and down and you move to that direction. So, that is also a good system in my opinion, because it really brings you whole body into the equation and the movement feels a little bit more real.

Although there are options, or there are things you might want to avoid. For example, you wouldn’t want to do something like an ice skating where if you want to stop, and stop moving your arms, if the player keeps like an inertia in that direction I feel like that would make people sick because that is what I saw with the Other World experience was that when I, also when I, when I didn’t let the player fully control the movement it gave the people that I tried this on, it gave them a bit motion sickness, including myself.

You can also have other interactions. There’s really no limits to the things you can do. In this particular case, using the hands to climb actually felt very comfortable, I was standing up, and it was similar to how you would be climbing in real life. But, I guess the heights could make some, some people sick.

So, that brings me again to the beginning which is that you have to test your idea and your prototype with many people, if possible go to a crowded place and just set up your equipment and be, “Free virtual reality testing” and just, people that walk by just get, see what they do.

And it’s not just about what they say it’s also how they interact with the game. What is of use, what is not of use? Like, if you really have to explain it to them it means that something is not working. The game should be self-explanatory or should have some sort of in-game tutorial that teaches the people how to play. Because once your game is out, or your experience, or applications out, you’re not going to be there to teach them how to play. So, ideally you want to help them feel comfortable with the game and learn how interact with your virtual environment.

Alright, so I’ll leave some links in the notes if you want to read more about motion sickness, or simulator sickness and, this, all of this lesson. And, I will see you in the next video.

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