Touch-screen technology has become wildly popular, thanks to smart phones designed for nimble fingers. But most touch screens have a major drawback: you need to keep a close eye on the screen as you tap, to make sure that you hit the right virtual buttons. As touch screens become more popular in other contexts, such as in-car navigation and entertainment systems, this lack of sensory feedback could become a dangerous distraction.

Now researchers at Carnegie Mellon University have developed buttons that pop out from a touch-screen surface. The design retains the dynamic display capabilities of a normal touch screen but can also produce tactile buttons for certain functions.

Graduate student Chris Harrison and computer-science professor Scott Hudson have built a handful of proof-of-concept displays with the morphing buttons. The screens are covered in semitransparent latex, which sits on top of an acrylic plate with shaped holes and an air chamber connected to a pump. When the pump is off, the screen is flat; when it's switched on, the latex forms concave or convex features around the cutouts, depending on negative or positive pressure.

To illuminate the screens and give them multitouch capabilities, the researchers use projectors, infrared light, and cameras positioned below the surface. The projectors cast images onto the screens while the cameras sense infrared light scattered by fingers at the surface.

The idea of physically dynamic interfaces isn't new, and in recent years, researchers have explored using screens made from polymers that can alter their shape when exposed to heat, light, and changes in a magnetic field. However, these materials are still experimental and relatively expensive to make.

Simpler systems, such as those that use a flexible material like latex and a pneumatic pump, have also been explored by researchers in the past. However, these systems haven't had all the capabilities of the Carnegie Mellon project, Harrison says. He explains that the display is the first to combine moving parts (the pop-up buttons), display dynamic information, and be touch sensitive. Other projects and products usually achieve two of these three criteria, he says.

"Microsoft Surface does graphics, and you can touch it, but it's totally fixed," Harrison says. "Buttons on a dashboard have great tactile input, but there's no display. And it's not like you can just deform an LCD screen and . . . make it electrically conductive at the same time."