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British Software Helps Disabled to Type - 2002-08-22

For most of us, communicating by written word is as easy as using a computer, typewriter, or simple pen and paper. But some disabled people who can't easily use a keyboard or hold a pen have fewer options for written communication. New computer software developed in Britain opens up a world of possibilities for the disabled by letting them type using nothing more than a computer mouse, trackball or even just the movement of their eyes.

Computer keyboards and typewriters are communication tools that most of us use regularly in our jobs. They've worked for many years and they're likely to be around for many more. But do you sometimes wish there were a better way to put your thoughts into words? David MacKay did. He's a reader in Natural Philosophy with the Physics Department at Cambridge University in England. In December 1997, while on a bus trip to Denver, Colorado, he and one of his American colleagues discussed some problems with the standard keyboard. "How could we make a text entry system that's smaller than a keyboard? How could we make a miniature device where you could write nearly as fast as with a keyboard, but on something much smaller? At the same time, we were also motivated by the idea of providing text entry systems for people who can't use keyboards; disabled people for example," he said.

When Mr. MacKay returned home, he wrote the code for his new typing interface called "Dasher." The first version of the software involved only a crosshair and the letters of the alphabet on the screen. It was designed to work with a computer's mouse. The user moved the mouse to scroll through the letters, and selected the ones needed to form the desired words.

The basic design for Dasher's writing interface was established, but David MacKay says there was still a piece missing. "When you're writing English, you're writing something that's very redundant. There's a lot of predictability in English text. And yet computers for the most part don't take advantage of that predictability, so it's easy to make spelling mistakes if you hit the wrong key for example. But we didn't want something that forces its spelling corrections on you," he said.

So Mr. MacKay and David Gray, one of his Ph.D. students, focused on building language predictability into the software. As you select characters, Dasher tries to guess what you want to write, and it's fairly accurate.

Working with Dasher is like searching through a library of common words. Instead of manually selecting individual letters to form each word, users let the software suggest the words, which then become part of the text. While it is slower for most people than typing, the Dasher interface works well with any mouse-like pointing equipment.

David Mackay's writing technology can also work in response to simple eye movements when used in combination with an eyetracker. An eyetracker is a device that places the mouse-pointer or cursor directly where your eyes are trained on the computer screen. From the tests conducted so far, Mr. MacKay says that most of his subjects prefer using a mouse over the eyetracker if they can, because it's usually faster for them.

"In the long-term, we're hoping that it will be faster with the eyetracker than the mouse, because that cuts out an extra control loop in the human hardware that's involved. At the moment the fastest we've had is with the mouse, and David Ward can write at 39 words per minute," he said.

Since David Ward co-developed the software, he's probably more accustomed than most people to writing with Dasher. But anyone curious about the software can download it from the Cambridge University web page and try it out at no cost. Mr. MacKay is currently distributing the software for unlimited free use. He is also inviting anyone to improve or redesign the Dasher program for their own use.