As touch screens shrink, one of the biggest problems users face is that their fingers cover up what they're trying to look at. An experimental setup from researchers at Microsoft and Mitsubishi lets people essentially touch their screens from the back. A semitransparent image of their fingers is superimposed on the front of the display.

To build their prototype, the researchers glued a touch pad to the back of a conventional touch-screen device; then they added a Web camera that captures an image of the user's hand. Software creates the semitransparent representation of the hand, correlating its position with that of the real hand. Having built an experimental but admittedly impractical version of the device, the researchers are now exploring versions that could be commercially ­viable. One approach involves a touch pad with an array of capacitors whose electrical charge is altered by the proximity of the user's fingers. In another, arrays of single-pixel light sensors would map the fingers' location.