Dynamic FOV In VR: Why Those Blinders In Eagle Flight Are Your Best Friend

Note the black borders. Image Source: vrtodaymagazine.com

The other day I watched an IGN review for Ubisoft’s latest VR game, Eagle Flight. The game itself looks like great fun and the reviewer did an excellent job covering the pros and cons of the title itself.

But there was one thing that he failed to mention, and it is something that I think a lot of new VR enthusiasts may be wondering: just what the hell is that black stuff covering up large portions of the screen during gameplay?!?

Notice how the Field of View constricts and adjusts in tandem with the user’s head movements. Video Source: Youtube

Above is a 16-second clip of Eagle Flight gameplay. Notice that as a player tilts their head (which is how turning is accomplished in “Eagle Flight”), the direction they tilt towards becomes partially blocked by a black hue. In VR, this covering is known as a Dynamic FOV adjustment and it is critical to staving off the effects of motion sickness and nausea (otherwise known as VR sickness). Besides being quite effective at mitigating VR sickness, Dynamic FOV adjustments are barely noticeable in headset, despite the fact that they are highly noticeable on a 2D monitor.

What Causes VR Sickness?

The overlying theory behind VR sickness is called the Sensory Conflict Theory, which in layman’s terms, means that there is a disconnect between what your eyes perceive as movement and what your vestibular system (those bits in your inner ear that give you a sense of balance and orientation) perceives as non-movement.

So when your visual cortex is being sent signals that say YOU’RE AN EAGLE SOARING OVER PARIS at the exact same time that your vestibular system is saying YOU’RE A SILLY HUMAN SITTING STILL IN A DESKCHAIR, you’re brain is likely to get confused and make you feel ill.

Image Source: TechRadar

Some even theorize that the specific bodily inducement of nausea is the result of your brain misinterpreting disorientation as a possible side-effect of poisoning, and thus the desire for oral ejection is actually the body trying to purge any potential contaminants.

How Do Dynamic FOV Adjustments Mitigate VR Sickness?

So first off, it is important to understand that Field of View (or FOV) refers to the degree to which the observable game world can be contained by the screen (or screens) in front of your eyes.

Image Source: VR Lens Lab

In real life, the average person can see roughly 200°-220° around them without moving their head. In VR however, that viewing area is constrained to an area typically between 90°-100°. There are a number of reasons for this (many dealing with the cost of better technologies), but one of the most important reasons is the proven relationship between increased FOV and increased nausea in headsets.

Think of it like this. If your brain is already having trouble understanding why the visual stimuli in front of your eyes seems incongruous to the information that is being sent by your vestibular system, then adding more visual stimuli (with a wider FOV) is only going to make you sicker. It’s just more incongruous content for your brain to try and analyze. If, however, you decrease the FOV and limit the amount of incongruous stimuli, then your brain is more capable of understanding what is happening.

Furthermore, smaller FOV’s also mean that more of your real-life-human field of vision remains static, and that static image gives the brain something to hold on to and use as a means of understanding the surrounding environment. In Jason Jerald’s “The VR Book”, he states that “Humans have a strong bias toward worlds that are stationary. If some visual cues can be presented that are consistent with the vestibular system, motion sickness can be reduced” (pg. 205). Jerald calls these visual cues Rest Frames.

“Humans have a strong bias toward worlds that are stationary” — The VR Book

I called Jerald up to ask what he meant by this and he put it quite simply. “When you’re playing a first-person game on a computer,” he said, “you may be moving erratically on screen, but because the world outside the the game — the edge of the monitor, the desk it’s sitting on, and so forth — are all stationary, you feel grounded and your vestibular system does not get confused like it does when you’re in a VR headset.”

Eagle Flight’s systems function in a very similar manner, except that they react directly what what you’re doing on screen. When you’re making a turn, or moving very rapidly past buildings (the kind of thing that in real life gives you a very strong sense of nausea-inducing vection, or speed), blinders pop up on the sides of your eagle view, giving you a visual response to something that you’d usually have a physical response to.

These blinders provide your visual cortex with something that is just as static as your vestibular system thinks you are, and it gives you a solid sense that YOU (and your blinders) ARE MOVING FORWARD THROUGH THE WORLD, rather than the sense that THE WORLD IS MOVING BACKWARDS AROUND THE STATIONARY YOU.

Are FOV Adjustments Distracting In-Game?

No. In fact, they’re barely noticeable in game and overall they allow for enhanced immersion.

Earlier this year Ajoy Fernandes and Steven K. Feiner of Columbia University wrote an award-winning paper titled “Combating VR Sickness through Subtle Dynamic Field-Of-View Modification”. While this paper seems completely separate from the work done by Ubisoft with Eagle Flight, the basic concepts are shockingly similar. In their paper, Fernandes and Feiner stated that the primary issue surrounding VR FOV was that higher FOVs were required to generate higher levels of immersion (or presence), but that immersion came at a significant cost, which was that higher FOVs also greatly increased nausea.

To tackle this problem, they proposed the concept of Dynamically adjusting FOV.

Image from the Columbia University Study. On the left is the unobstructed FOV, on the right is the FOV as it’s being dynamically adjusted based on user input (speed and direction of movement).

Their findings won them the “Best Paper” award at theIEEE Symposium on 3D User Interfaces. Besides simply demonstrating the effectiveness of Dynamic FOV adjustments, the team also measured users abilities to perceive the adjustments in-headset. According to the paper “FOV restrictors were unnoticed by the majority of participants, with 15 out of 30 participants selecting 1 (definitively stating “Did not notice or did not happen”) in response to whether they noticed the FOV decrease during the session in which they experienced the FOV restrictors. . Furthermore, 11 of 15 R-90 participants (those whose field of view was only diminished to 90°) marked a 1 for FOV change…clearly indicating that it was imperceptible to the majority experiencing that condition” (pg. 210) .

The fact is that while this technique may seem glaringly obvious on a standard monitor, in headset it is anything but.

Wrap-Up

Dynamically adjusting the Field of View while in headset is one of the best ways to mitigate nausea in VR, and while it may look highly apparent (and even annoying) when presented on a 2D monitor, it is barely noticeable in a headset and certainly worth the high levels of comfort and non-pukey feelings that it provides.

Job well done Eagle Flight.

**Written by Nathan Hoffmeier

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