For all its designer appeal, Apple's forthcoming iPhone is lacking. While the touch-screen interface looks beautiful, it will most likely suffer from the same drawback that plagues many other mobile gadgets with touch screens: no tactile feedback. A button on a flat, slick display simply doesn't feel like a button, and as a result, people are prone to making errors with them.

But within the next few years, those faux touch-screen buttons could feel more like real buttons, thanks to research at a handful of universities and companies that are investigating touch-based feedback from gadgets. By feeling a buzz when they press a button correctly, people become more accurate typists on touch-screen keyboards, says Stephen Brewster, professor of computing science at the University of Glasgow, in the United Kingdom. Brewster and his team have found that people err--mistype, double-press, or slip from one button to another--up to 25 percent less frequently when vibrations are used to let them know that they've pressed a button correctly.

"The basic thing we show," Brewster says, "is that having tactile feedback makes [mobile devices] more useful and usable." Without tactile feedback, he says, people are still going to have usability issues no matter how well the touch screen is designed to ignore extra touches or accidental taps. In addition to trying to get rid of errors, Brewster and his team are exploring how well different types of vibrations convey various kinds of information, such as the urgency of an e-mail.

Today, almost all phones have the ability to buzz when someone calls. But this kind of vibration amounts to an announcement. The idea of using vibrations as feedback is a relatively new one and comes from an emerging research area called haptics, technology that involves human-machine interactions based on touch. Haptics is being explored for a range of applications, from mobile-device feedback to remote surgery. (See "The Cutting Edge of Haptics.")

A San Jose­based company called Immersion is using haptics in a number of applications, and it has already developed haptic technology for Samsung mobile phones on the market today. The basic idea behind Brewster's research and the technology from Immersion is the same: when a button on a touch screen is pressed, actuators inside or on the phone vibrate. In both cases, the vibration doesn't occur solely underneath the user's finger. Instead, the whole phone vibrates, which effectively creates the sensation of a button below the pressing finger, says Brewster.

While Immersion's technology currently uses the same, somewhat limited actuators that are employed when a call is received, Brewster's team is using specialized, somewhat expensive actuators to explore how people respond to different types of vibrations. Research conducted by Eve Hoggan , a PhD student in Brewster's group, has shown that people can distinguish among different types of vibrations. A vibration can feel rough or smooth depending on the shape of the electrical current used to power the actuator. In some cases, the shape of the current can create a smooth vibration (when the waveform is a sine wave), and in other cases, the current produces a rough vibration (when the waveform is a sawtooth wave).