MAbrash GDC2013 (22)

Tracking and latency are just prerequisites.

Once you have good enough tracking and latency, you can draw in the right place at the right time; then you learn about all the other interactions of displays with the human perceptual system.

The key here is that the way displays present photons to the eyes is nothing like the real world, and it’s a miracle we can see anything coherent in displayed images at all.

In the real world, objects emit or reflect photons continuously.

On a display, pixels emit fixed streams of photons for discrete periods of time.

Pixels are also fixed in space relative to the head.

This has major implications; let’s look at a couple of them.

MAbrash GDC2013 (23)

For the following discussion, it will be useful to understand some very simple space-time diagrams, like the one shown here.

The horizontal axis is x position relative to the eyes, and the vertical axis is time, advancing down the slide.

You can think of these diagrams as showing how an object or an image would move horizontally across your field of view as time passes.

You can also find a discussion of space-time diagrams on my blog; I’ll give the URL at the end of the talk.

In this diagram we have an object that is not moving relative to the eyes. The plot is a vertical line because there’s no change in x position over time.

It’s important to understand that the x position in these diagrams is relative to the position and orientation of the eyes, rather than the real world, because the eyes’ frame of reference is what matters in terms of perception. So this diagram could be a case where both the eyes and the object are unmoving, or it could be a case where the eyes are smoothly tracking an object as it moves. In either case, the object would remain in the same x position relative to the eyes.

MAbrash GDC2013 (24)

This diagram shows a real-world object that’s moving from left to right at a constant speed relative to the viewer, while the eyes remain fixated straight ahead – that is, the eyes aren’t tracking the moving object. Here’s an example of the sort of movement this diagram depicts.

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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

      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. :)