MAbrash GDC2013 (34)

This is half persistence, where pixels remain lit for half the frame.

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And this is zero persistence, where pixels are lit for only a tiny fraction of the frame – but with very high intensity to compensate for the short duration.

Both OLEDs and LCDs can be full persistence or less.

Scanning lasers are effectively zero persistence.

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Now we come to the crux of the matter.

High persistence, together with relatively low frame rate, causes what cinematographers call “judder”, a mix of smearing and strobing. This diagram shows why.

Here we see the case where the eyes track a virtual object that’s moving across the display. This could involve tracking a virtual object that appears to be moving through space, or it could involve turning the head – to which the display is attached – while fixating on a virtual object that isn’t moving relative to the real world. The second case is particularly important for two reasons: one reason is that we tend to turn to look at new things by moving our eyes first, then fixating on the new target while the head rotates to catch up, and the second reason is that the relative speed between the display and the eyes can be an order of magnitude faster when the head rotates than when tracking a moving object without the head turning, with correspondingly larger artifacts.

Ideally, the virtual object would stay in exactly the same position relative to the eyes as the eyes move. However, the display only updates once a frame, so, as this diagram shows, with full persistence the virtual object slides away from the correct location for the duration of a frame as the eyes move relative to the display, snaps back to the right location at the start of the next frame, and then starts to slide away again.

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  • 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


      Thank you very much for posting this!


  • 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


        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.


  • 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. :)