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This slide illustrates the relative motion between an eye and the display. Here the eye counter-rotates to remain fixated on a tree in the real world, while the head, and consequently the head mounted display, rotates 20 degrees, something that can easily happen in a hundred milliseconds or less. The red dot shows the pixel on the display that maps to the tree’s perceived location in the real world, and thus the orientation of the eye, before and after rotation, with the original position shown with a faint red dot in the right-hand diagram. You can see that the red dot shifts a considerable distance during the rotation. While it’s true that the effect is exaggerated here because the tree is about six inches away, it’s also true that the eyes and the display can move a long way relative to one another in a short period of time.

This rapid relative motion makes it very challenging to keep virtual images in fixed positions relative to the real world, and matters are complicated by the fact that displays only update once a frame.

That results in a set of major issues for VR that don’t exist in the real world, and that are barely noticeable at worst on monitors, because there are no useful cases in which your eyes move very quickly relative to a monitor while still being able to see clearly.

Much of the rest of this talk will be dedicated to exploring some of the implications of the relationships between a head-mounted display, the eyes, and the real world.

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The first implication has to do with tracking.

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By tracking, I mean the determination of head position and orientation in the real world, known as pose.

Images have to be in exactly the right place relative to both the head and the real world every frame in order to seem real; otherwise the visual system will detect an anomaly, no matter how brief it is, and that will destroy the illusion of reality.

The human perceptual system has evolved to be very effective at detecting such anomalies, because anomalies might be thinking about eating you, or might be tasty.

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Ben Lang
Ben is the world's most senior professional analyst solely dedicated to the XR industry, having founded Road to VR in 2011—a year before the Oculus Kickstarter sparked a resurgence that led to the modern XR landscape. He has authored more than 3,000 articles chronicling the evolution of the XR industry over more than a decade. With that unique perspective, Ben has been consistently recognized as one of the most influential voices in XR, giving keynotes and joining panel and podcast discussions at key industry events. He is a self-described "journalist and analyst, not evangelist."
  • WormSlayer

    My brain hurts! Still I’m excited that guys like him are excited :D

  • Patrick Hogenboom

    Thanks a bundle for transcribing the whole thing :)

  • shole

    If you want to view the two videos in the presentation and don’t have ms powerpoint, you can rename the .pptx file to .zip and the files are in there as .wmv under \ppt\media\

    • Michael Abrash

      Shole,

      Thank you very much for posting this!

      –Michael

  • Andrés

    Thanks so much for transcribing this!

  • Andreas Aronsson

    I thought I would not get to read/hear the actual talk in some time :D Very interesting, somewhat alarming, but at the end uplifting and inspiring! Thanks for this! Also, you could if you wanted to rename the .pptx to .zip and extract the videos (media folder) and upload them unlisted to Youtube and embed them on this page :) Just a thought!

  • Andreas Aronsson

    Ah, in the time it took me to read this (left the article half-read over night) shole already pointed this out :x oops.

  • Esse

    “That means that if you fixate on something while you turn your head, your eyes remain fixed with respect to the real world, but move very quickly relative to the display”

    Hum, no. If your eyes are fixed (in the head referential), they are fixed in the display referential. Because the display & the head are fixed one to the other.

    This is over complicating the subject. Only matters the head movement. Not the eyes movements.

    • Ben

      I think that, in this context, “fixate on something” means a visual fixation on an object in the external world rather than having the eyes be “fixed” relative to the head. If the head is turning while you fixate an external object, the eyes must counter-rotate in order to maintain a stable fixation (eg: via the VOR). Since the VR display is attached to your head frame, this means that your eyes are rotating relative to the display, and that’s the source of the large relative motion that causes issues.

      • Michael Abrash

        Ben,

        You’re correct – that’s what I meant. If you look at a key on the keyboard and keep doing that while you turn your head, you can easily get your eyes moving at several hundred degrees per second relative to the display.

        –Michael

  • Esse

    “The human perceptual system has evolved to be very effective at detecting such anomalies, because anomalies might be thinking about eating you, or might be tasty.”

    It is not some specific “anomalies detection system”, rather that the human brain has in-depth “routines” to analyse the space & movement, and when you broke the rules the routines fail.

    Like when you are sick in a car.

    So I guess the reaction will not be fear or drooling, more puking.

  • Ben Humberston

    Thanks for the transcript for those of us who couldn’t be there!

  • Mattso

    Yeah, just echoing the sentiments above that having it all transcribed meant I actually got to digest it really quickly. Many thanks!

    Very informative stuff – and here was me thinking it was gonna be easy. :)