Motion Sickness in VR

Over the last few years, VR in the gaming section has almost become mainstream, although it’s still a challenge to make it as comfortable as it is desired. While usually, the main focus for developing a game is on the graphics or the story, for VR games it is getting rid of the motion sickness. This article covers everything around motion sickness, its origins and how to reduce it in VR games.

At the GDC (a summary of this year’s conference can be found here) in 2017, a very popular game studio held a talk about how motion sickness works and what that means for the work of game developers. Here, I have summarized it for you and picked out the most valuable information as it relates to motion sickness and the development process of their newest VR game:

The talk of Oliver Palmieri contains a lot of information about what you should do in VR and what you really shouldn’t. In order to develop Eagle Flight, a VR game which lets you become an eagle and gives you the opportunity to fly, Ubisoft put extra effort in the R&D of avoiding motion sickness. To fix the bad feeling while or after playing VR games, you have to understand what is going on in the body from an organic perspective. Regarding this, Palmieri mentioned three points:

  • – The Inner Ear
  • – Saccadic Eyes Motion
  • – Vestibulo-Ocular Reflex

The Inner Ear

The inner ear or internal ear is located at the innermost point of the ear and is responsible for sound detection and balance. The special form of it lets us detect the three main axes – X, Y and Z – so we always know our head’s exact position.

Saccadic Eyes Motion

Our eyes have a so-called saccadic behaviour when following a moving object. Ubisoft found out that this effect does not only occur when the head is fixed and the eyes are following an object, but also when the body is rotated and the eyes are made to focus on the things directly in front of them.

Vestibulo-Ocular Reflex

In their study, they found out that there is a strong connection between the ears and eyes. If the head is moving, the eyes are adjusting in a reflexive way. If the inner ear is detecting a movement of the head while the eyes are focusing on a certain point, the eyes are adjusted so that the point is still focused.

The main conclusion of the research was that ears and eyes work together and if any motion is not detected by both parts, the brain implies that something is wrong. With this knowledge, the team defined their desired solution for this project as follows:

  • – Best VR comfort
  • – Accessibility / Intuitiveness
  • – Precision / Reactivity

Eagle Flight Development Process & Motion Sickness Reduction

In the first version of the game, Ubisoft just focused on controls and basic gameplay comfort. Even though early stages of the demo were quite successful and got positive feedback from gamers and non-gamers alike. The controls were basically the head movement of the player without any controllers, due to the fact that controlling 3d with a 2d joystick felt unintuitive. Very soon, however, testers got sick while playing and the team came to the conclusion that the fact that the players saw things which didn’t correlate with what their sense of balance detected, made them sick. They came up with two ways to make you feel sick: Feeling motion, but not seeing it and seeing motion, but not feeling it. Those two points mapped onto VR games and especially onto Eagle Flight led to five main causes for VR discomfort:

  • – Vision / Inner ear conflicts
  • – Visual continuity not met
  • – Fast motion in close proximity
  • – Visual perception only of acceleration
  • – Brain expectations of collision

After that feedback, a lot of effort was put into the aspect of motion, how it was presented to the player and which techniques could reduce the motion sickness to make playing the game as comfortable as possible.

Head Position

The player’s head position controls the flight direction of the eagle in the game and thus the head position had to be respected, which means it is not allowed to show movements which aren’t done by the players themselves.

Forward Vection

Vection is the perception of motion, e.g. flying in Eagle Flight. This forward vection had to be constant and linear, which means that the acceleration or deceleration wasn’t changed abruptly, like for example suddenly stopping in mid-air.

Continuous motion

Slow acceleration and deceleration works quite well, but sudden stops are not comfortable, because the visual motion doesn’t fit the information the brain gets from the inner ear. If the player crashes into a wall the game, changing direction quickly or stopping is not allowed. So, in order avoid this behaviour a fade to black is shown to the player.

Nose

Your brain is very used to seeing your own nose, even if you don’t consciously see it. To bring back this familiar reference point, a bird nose was added to the view. The behaviour was the same, the player didn’t really see the nose at the lower part of the view, because the brain just faded it out very quickly.

Keep The Brain Busy

If the brain is busy, it doesn’t have that much time to think about the correlation of visual perception and ear balance. The consequence of this is reduced motion sickness.

Sounds

Not only visual effects like the nose as reference point let the brain believe that something is real, but also sounds can have an influence. In Eagle Flight, the sound of wind was implemented very carefully. Heading to the right makes a different sound than heading left, which is kind of a reference point as well.

All those points combined mean that the game can be played without getting sick at all.

Relevance Of Motion Sickness

Motion sickness became a well-known word among gamers, even though this phenomenon is, of course, also happening all the time at other places. Palmieri mentioned that wearing glasses for the first time makes you feel uncomfortable for two to three weeks. The eyes experience unusual visions which have to be re-considered normal for the brain, which takes some time. The same effect takes place with space or sea sickness. The body experiences motions which are not controlled by the own body and gets sick.

The Function Of Motion Sickness

According to George Crampton, the author of “Motion and space sickness, motion sickness has no function which is needed in order to survive. The result of motion sickness is vomiting and the only apparent function of vomiting is the removal of the contents of the stomach. Thus, in order to get rid of poison in the stomach, the body gives you the feeling of nausea, which is the same feeling you get if you encounter motion sickness. We can conclude that “vestibulo-gastric illness” (i.e. motion sickness) somehow correlates with the instinctive behaviour of handling poisoning.

The topic around motion sickness is not only of interest to VR game developers, but also to many other areas in real life or research. Therefore, there is lots of scientific content available which can be used to implement a reduction of motion sickness for VR games.

With this knowledge about motion sickness and how to avoid or at least reduce it in VR games, the experience will be much better for the gamers, which leads to better reviews and overall reputations. I’m really looking forward to all the great games that will come out in the next few months and years!