Walk forwards or backwards, left or right. It makes no difference. Whatever direction you walk in, the omni-directional treadmill, developed by Virtual Space Devices, moves beneath your feet to match where you're going. It's like a real-life holodeck. Check out the video.
When I first watched it I was skeptical that the machine could actually do what its makers were claiming. For instance, it seemed to me that the guy in the video spends a lot more time walking left and right than he does going north and south. And perhaps it's all just some kind of camera trick
But after browsing through a technical paper about the invention (click the pdf link in the top right of this page to find the paper), I'm more convinced that it's real. The paper isn't easy to understand, but this passage offers an explanation of how the machine works:
The basic principle of the ODT consists of two perpendicular treadmills, one inside of the other. The top belt, comprised of an array of freely rotating rollers lies atop a second, orthogonally oriented belt also comprised of rollers. Each belt is made from approximately 3400 separate rollers, woven together into a mechanical fabric... Because both the top roller belt and the bottom roller belt are bi-directional, all planar vectors may be generated. The surface moves in any direction, allowing the user to walk a circular path if desired. When the user is moving, the entire active surface area is in motion. The user’s feet contact multiple active rollers, thus creating the effect of a flat and uniform surface.
I really don't understand the mechanics of it, but they sound like they know what they're talking about. And in this case, when combined with the video evidence of the machine actually working, that's going to have to be good enough.