Why Multiple Displays are (much) Better than VR Headsets

September 27th, 2022

About VR Headsets

There is increasing interest in using new generation “Virtual Reality” (VR) Headsets such as Facebook’s “Oculus” and HTC’s “Vive” as display devices for simulator-based training.

The idea is simple: when you turn your head, movement is detected by “head-tracking” electronics in the headset and then transmitted to your computer. After that, your computer “re-draws” what you see on the two small displays in front of your eyes. The problem is, lots of people experience motion sickness when objects are moving in the simulated world, especially when you are moving too e.g. at the controls of (simulated) mobile equipment.   (Indeed, one automotive manufacturer told us that he had to “mothball” his VR simulator because 80% of trainees experienced such motion sickness.)

The most obvious symptom of such motion sickness is nausea but others are blurred vision, vertigo, dizziness, fatigue and headache, even hours later.

Well, that motion sickness is due to two different problems [1], [2].

First, when wearing a VR Headset, your field-of-view is limited to what’s directly in front of you, much like the “blinders” that prevent a racehorse from seeing side-to-side. For that reason, you must turn your head to “see” left and right, and to look up and down.

The fact is, for training simulation to be effective, all sensory cues must work together, and that leads to the second problem, namely the time delay between turning your head and “seeing” in the new direction (also called “lag” or “latency”), because typical computers just can’t “keep up” with typical head movements.  

Here are the technical details: “frame rate” refers to the number of times, per second, that your computer “notices” the movement of your head, “decides” what to change now that you are looking in a new direction, performs lots of calculations associated with those changes, and finally “re-draws” what you see inside the VR Headset. And to avoid motion sickness, the frame rate must be very high e.g. 90 Hz, and that requires lots and lots of computing horsepower.  

(You can mitigate the time delay problem in two ways: first, by learning to turn your head s-l-o-w-l-y, and second, by training for just a few minutes at a time. Clearly, both “solutions” will greatly impact your simulator-based training.)

Why Multiple Displays are (much) Better

In the real world, you can turn your head as quickly as you want and you always see something new, i.e. there is no “time delay”.

More importantly, when you look forwards, you see not just forwards but also left and right and up and down. And that peripheral vision is key to operating real heavy equipment in the real world, whether you’re working with a forklift to place a palletized load on a shelf, or working with an excavator to dump material into the bed of a haul truck.

The fact is, you count on being able to see to the left and right and up and down while you work, and that’s why preserving a “natural” field-of-view is so important for simulator-based training.

Indeed, you can do just that with three “big screen” displays set up in front of your simulator controls to provide a panoramic field of view of 180 degrees. (And when it’s important to turn your head to look backwards when moving backwards, just add another “big screen” display set up behind your simulator controls.)

Fortunately, the growing popularity of home entertainment systems has brought the price of off-the-shelf HD (and now 4K) “flat screen” TVs within the reach of every training budget, even as the size of popular models continues to increase from 42” to 55” to 65” or more. (Bigger displays “fill up” even more of your field of view, making the simulation experience even more “immersive”.)

And you’ll find that the price of four such displays can be less than the price of a single VR Headset.

Six More Reasons Why Multiple Displays are (much) Better

We can identify six additional limitations associated with VR Headsets.

  1. Wearing a VR Headset limits what you see to just the simulated world. For this reason, it can be difficult, for example, to reach for a forklift lever with your right hand (in the real world) because you cannot “see” the lever or your hand. (More expensive VR Headsets attempt to overcome this problem by adding cameras to “superimpose” what the cameras “see” on top of the simulated world to create “augmented reality”, at added cost. Alternatively, there are VR “gloves” with built-in sensors to “capture” the position and movement of your hands, in order to create virtual hands that can be seen the simulated world presented inside the VR Headset.)
  2. The weight on your head, and the display fitting tightly over your eyes (to block out the real world around you), make VR Headsets uncomfortable to wear for the extended periods of time required for simulator-based training.
  3. The VR Headset must be connected by a cable to your computer (wireless connections are too slow) and that cable can “get in the way” when you move your head.
  4. When wearing a VR Headset, only youcan “see” what’s going on. So if an instructor wants to monitor your progress by watching you work, that instructor will need some kind of conventional display in any case, at additional cost.
  5. Because the displays inside the VR Headset are so close to your eyes, the visual display appears “pixelated”, i.e. you can notice the tiny picture elements (pixels) that together create the visual presentation. This isn’t a problem with big screen displays because they are positioned much farther away from your eyes, and so the perceived visual quality is superior.
  6. When sharing a single simulator “station” among many trainees, the VR Headset must be adjusted each time (everyone’s head is different), and that means extra wear-and-tear that can quickly lead to damage, not to mention problems associated with personal hygiene. (This is especially problematic with COVID-19 still with us.)

Clearly, using multiple displays has none of these limitations.

One more thing: a recent review of the scientific research about VR Headsets for education and training [3] concluded that when it comes to developing psycho-motor skills [e.g. for operating heavy equipment], they have

“… no advantage [compared to multiple displays] and in some cases even proved counter-productive because of widespread cyber-sickness, technological challenges, or because the VR experience distracted from the learning task.”

The Bottom Line

Consider this: more of your brain is devoted to processing what you see than the combination of what you hear and touch and smell. And because what you see is so important, multiple “big screen” displays will always deliver superior support for hour-after-hour simulator-based training.

The fact is, today’s VR Headsets are simply too “primitive”, too fragile, and too costly for “industrial strength” simulator-based training. And although that technology is improving (slowly), off-the-shelf “flat screen” TVs are increasing in size much faster, and at prices that continue to fall. Practically, this means that “filling up” your field of view with multiple displays has never been so affordable.

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References

1] “The Science of Simulation”, MS&T – The International Defense Training Journal, Halldale Group, June 2019, 

[2] “The Virtual Reality Head-Mounted Display Oculus Rift Induces Motion Sickness”, J. Munafo, M. Diedrick, T. Stoffregen, Experimental Brain Research, Volume 235, Issue 3, 2017.

[3] “A Review of the Use of Virtual Reality Head-Mounted Displays in Education and Training”, L. Jensen, F. Konradsen, Education and Information Technologies, Volume 23, 2018.