How? The screen actually moves.
You can see this in action in the video below; there are wires at each corner which work in concert to pull the screen in the necessary direction. By varying how sharply the screen moves a feeling of impulse or momentum can be conveyed to the user. In the demo users interact with floating balls and the speed and direction of a ball determines what sort of motion the screen makes; as a result users experience the balls “hitting” their fingers.
In the video a representative indicates that navigation is an obvious application for this sort of touchscreen, as it could impart directional information even if you can’t take your eyes off the road. Of course basic interaction like typing on a virtual keyboard could also be enhanced, probably with a more realistic tactile experience than a short vibration of the screen can convey.
While NEC’s system doesn’t convey texture the way electric-field touchscreens can, for some uses (like navigation) directionality may be more important. It also may depend on which solution is easier (and therefore more cost effective) to produce and implement. If NEC can get production of their new moving touchscreens up to speed quickly, you may see them in person in the not-too-distant future.
source: DigInfo via Engadget