The disease of movement and the physics of virtual reality

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Virtual reality technology has experienced rapid improvement in recent years as its applicability expands to more areas and big players get involved. However, VR technology still has some flaws that are extremely difficult to address. Overcoming these problems is essential to making a wider application possible. As many research groups try to take different approaches to these technical issues, an essential part of this is certainly a better understanding of the physics of human vision.

The problem of virtual reality

The movements of illness, dizziness, nausea, headache, etc. they are very common among VR users. A survey by Austrian virtual reality company Junge Römer showed that more than 75% of the 991 survey participants had experienced at least one of these symptoms. The survey also revealed that these negative effects were particularly strong for first-time users. In addition, there was an almost linear relationship between the persistence of these symptoms and the time of use.

In addition to providing a comfortable RV experience for entertaining purposes, the biggest motivation for scientists to invest in solving these problems is to enable the applicability of RV in areas such as medicine or education.

So the question is how can physics help us improve the virtual reality experience?

How do virtual reality headsets work?

In order to appreciate the role that physics plays in virtual reality, it is useful to review how virtual reality headsets and the human eye work.

Basically, what happens when you wear these stylish virtual reality glasses is that you look at a screen very close to your eyes that occupies the entire field of view of your eyes. However, your eye cannot focus on very close objects. To overcome this problem, we use complex optical systems, which consist mainly of lenses (read below) so that our eyes can focus on these objects.

The amount of light on the screen will pass through this optical system and then touch the view. Your eyepieces will bend this light to focus it on the retina at the back of the eye. In the next step, certain vision receptors will convert this amount of electromagnetic radiation into electrical pulses and transfer it to the brain.

In physics, we represent this situation using the so-called ray model (see image, right).

Typically, a simple VR optical system consists of a set of highly sensitive lenses (usually Fresnel lenses) sandwiched between the eye and a screen.

These goals are extremely important in these devices. Because? Remember that when you use a virtual reality headset, you are actually looking at a screen that is very close to your eye and not a real object. This is a challenge to the naked eye. You can easily prove it for yourself if you start with the phone screen at a certain distance and zoom in; it eventually becomes blurred. Also, if you keep it close enough for sure, you will surely feel eye fatigue and headaches. This is because you are pressing your eyes to do something that is not uncomfortable for you.

With VR headsets, how can we keep this screen so close to the eye, but still allow a clear picture? We plant complex optical elements, which consist of particular objectives, to make the necessary corrections.

However, our eyes are very sensitive and the optical elements used are far from perfect. Unfortunately, only a small degree of mismatch makes a big difference in the immersive power of virtual reality. In fact, because of these small imperfections, we still have people reporting experiences such as motion sickness, loss of eyes, dizziness, headache, and so on.

The problem of vergence-accommodation

A large part of the solution will be the solution of one of the most fundamental optical challenges: the so-called accommodation-vergence problem. Most VR developers consider this to be one of the three most difficult challenges, in addition to improving screen resolution and expanding the field of view.

Put a finger in front of your face and look at it. Two things will happen with your eyes. First, in a very short time, your eyes will be focused on the finger (this is accommodation) and then your eyes should be fixed, which means they should point to the finger (this is embarrassment). In the real world, our eyes adjust and move closer to the same point.

However, this is not the case with VR headsets. When you wear VR glasses, your eyes are always focused on the VR screen near you. On the other hand, the vergence will indicate the virtual object whose distance and location will change over time. This makes everything very uncomfortable for your eyes and is one of the reasons why you experience eye fatigue and nausea.

Solution to the problem

VR companies make a lot of effort to solve the vergence-hosting problem. What so far has taught us all efforts in this direction is that we must optically address this problem. We cannot avoid this with simple computer or technical tricks. This means that we need to integrate optical systems into future VR headsets that mimic the behavior of light in the real world.

One of the first ideas to address this issue was to create virtual reality devices that contained multiple screens instead of a single one. Each of these screens would have a different focal length and, as such, would show different parts of the virtual environment. However, this comes at a high price because multiple screens will keep the contrast low.

Later, VR developers focused their attention on adaptive optics. The idea was to replace traditional VR components that had a single focal length with flexible lenses in this regard, meaning that they could switch between different focal lengths on demand in less than a millisecond.

By mounting these lenses between the human eye and the VR screen the scientists were able to create a much better virtual experience and less negative effects for the human subject. Although adaptive optics places strict requirements on head positions, which makes it very impractical.

It seems that a Singapore company has taken this work a step further. Instead of throwing away the idea of ​​adaptive optics, they rely on it. In 2018 they developed software that can determine the optimal location for the focus in all virtual scenes. In addition, they introduced an infrared eye tracker to check where the user is looking and feed this information to mechanical actuators that can easily adjust their position.

A third popular approach to this problem is the so-called light field technology. The idea behind this approach is to project multiple views of the virtual object onto the single VR screen using two or more rays of light coming out of the incremental areas of that virtual object. These rays will be projected on the pixels of the screen. The downside is that the more light rays we need, the greater the number of pixels needed.

A final note

VR technology has experienced massive and rapid improvement in recent years. However, VR devices are still far from perfect. People still report problems like nausea, dizziness, dizziness, eye fatigue, and so on. after having a VR headset for a while. However subtle these problems may be, the importance of addressing them is obviously enormous if we want this technology to be applicable in areas such as science, medicine, education, and so on. Our work so far has convinced us that an essential part of this goal is to understand the physics of the human visual system and to develop VR optical systems in full compliance with it. However, given the efforts and investments companies are making in this technology, we have every reason to expect near-perfect VR headsets.

– Haxhi Pantina is a physicist and journalist.

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