Earlier this week, the humble computer mouse celebrated its 40th birthday. While surprisingly little has changed since Doug Engelbart, an engineer at Stanford Research Institute, in Palo Alto, CA, first demonstrated the mouse to a skeptical crowd in San Francisco, we may have already seen a few glimpses of the future of computer interfaces. If so, over the next few years, the future of the computer interface will likely revolve around touch.

Thanks to the popularity of the iPhone, the touch screen has gained recognition as a practical interface for computers. In the coming years, we may see increasingly useful variations on the same theme. A couple of projects, in particular, point the way toward interacting more easily with miniature touch screens, as well as with displays the size of walls.

One problem with devices like the iPhone is that users' fingers tend to cover up important information on the screen. Yet making touch screens much larger would make a device too bulky to slip discreetly into a pocket.

A project called nanoTouch, developed at Microsoft Research, tackles the challenges of adding touch sensitivity to ever-shrinking displays. Patrick Baudisch and his colleagues have added touch interaction to the back of devices that range in size from an iPod nano to a watch or a pendant. The researchers' concept is for a gadget to have a front that is entirely a display, a back that is entirely touch sensitive, and a side that features buttons.

To make the back of a gadget touch sensitive, the researchers added a capacitive surface, similar to those used on laptop touch pads. In one demonstration, the team shows that the interface can be used to play a first-person video game on a screen the size of a credit card. In another demo, the device produces a semitransparent image of a finger as if the device were completely see-through.

When a transparent finger or a cursor is shown onscreen, people can still operate the device reliably, says Baudisch, who is a part-time researcher at Microsoft Research and a professor of computer science and human-computer interaction at the Hasso Plattner Institute at Postdam University, in Germany.

Details of the device will be presented at the Computer Human Interaction conference in Boston next April. The researchers tested four sizes of square displays, measuring 2.4 inches, 1.2 inches, 0.6 inches, and 0.3 inches wide. They found that people could complete tasks at roughly the same speed using even the smallest display, and that they made about the same number of errors using all sizes of the device. Furthermore, the back-of-the-screen prototypes performed better than the smallest front-touch device.