Hoggan has found that people can recognize the difference in these vibrations 94 percent of the time. Moreover, people can distinguish 81 percent of the time among the vibrational frequencies of 6 hertz, 70 hertz, and 250 hertz. Knowing how people can recognize different types of vibrations could help expand the usefulness of a keyboard. For instance, if someone puts his or her finger on a touch-screen key, but it slips and the user lifts it from another key (which results in no character being entered), the feedback could be a rough vibration, indicating that the user has made an error. Moreover, different types of keys or functions could produce different types of vibrations.

Brewster and his team are exploring how the placement of the actuators in the phone can be useful. Brewster has placed four actuators on the edges of a phone, where a right-handed person would likely grip the gadget. He says that these actuators could be used, for instance, to denote the progress of a downloaded file: each actuator would vibrate in sequence, with each buzz less intense than the last, until the file has completely downloaded. Moreover, Brewster says, the actuators could be used to help people navigate. If the phone were equipped with global positioning sensors and the location of a destination were entered, the vibrations could help direct a person to the right or the left.

Danny Grant, vice president of research at Immersion, thinks that Brewster's research will keep pushing the capabilities of haptic feedback in mobile devices. "One of the things that we're hoping for with haptics is to convey information using different methods," Grant says. "Already, the screen is small, and a touch screen is worse because a finger blocks it. Using the sense of touch and conveying more information that way is a big win. Any work that shows the range we can achieve in information transfer is great."

Brewster suspects that within the next couple of years, vibrational feedback will be much more common, and people will be able to pick out the different types of vibrations they want to use on their phones, much as people now choose the wallpaper on their phone's screen.