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How Fast Does "Virtual Reality" Have To Be To Look Like "Actual Reality"?

January 7, 2013 | Telepresence Options

virtual-reality-helmet.jpgLow latency is important to an effective VR display but might not be everything.

For decades now, virtual reality has been a pipe dream concept, well ahead of the technology needed to realize it. Generating a convincing 3D world that precisely and instantly matches the head-tracked position of a player's gaze was well beyond the headsets that proliferated in research centers and on the market up through the '90s. It has only been recently that products like Sony's prototype gaming headset and the upcoming Oculus Rift have seriously attempted to create believable virtual reality headsets using modern head-tracking and display technology.

But there are some who think the technology in these systems still hasn't been developed far enough to create a truly believable, head-tracked virtual reality. Valve's Michael Abrash laid out this case in a detailed blog post last weekend, suggesting that VR headsets need a "Kobayashi Maru moment"�to solve the inherent problem of display latency that plagues current and upcoming headsets.

Current non-VR games usually bottom out at about 50 milliseconds (ms) of latency between a controller input and the time the pixels actually update. That's more than fine when viewing an image on a stationary screen, Abrash says, but VR systems need much better latency in order to trick the brain into thinking it's looking at a virtual world that completely surrounds the player wherever he or she looks. "The key to this is that virtual objects have to stay in very nearly the same perceived real-world locations as you move; that is, they have to register as being in almost exactly the right position all the time," Abrash writes. "Being right 99 percent of the time is no good, because the occasional mis-registration is precisely the sort of thing your visual system is designed to detect, and will stick out like a sore thumb."

To be nearly indistinguishable from reality, Abrash says a VR system should ideally have a delay of 15ms or even 7ms between the time a player moves their head and the time the player sees a new, corrected view of the scene. The Oculus Rift can achieve latency of about 30 or 40 milliseconds�under perfectly optimized conditions, according to creator Palmer Luckey (this doesn't take into account the added delay inherent in the physical display itself; more on that later). While Luckey acknowledges that this is slower than the "real world" modeling ideal, he says he thinks the Rift is more than capable of creating a convincing virtual world.

"The Rift developer kit has received a lot of positive feedback from those who've tried it, but there's no denying we're still a ways away from perfect VR," Luckey told Ars. "It's a difficult question, because 'convincing virtual reality' is very subjective... You can be very convincing without necessarily being indistinguishable from reality."

That certainly describes my experience with a prototype of the Oculus Rift at the Penny Arcade Expo in September. To me, the delay between my head movements was practically�unnoticeable and much smoother than any other VR headset I had tried before. I could tell I was looking at a screen, obviously, but it wasn't the kind of jarring, "which way am I facing" experience of some other VR systems. I did get a little nauseous during the experience, but that was more from using the controller to turn my view without moving my head, rather than any delay in the virtual world I was tilting my head in.

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