For people who cannot operate either a physical keyboard or mouse, several other options are available. These include voice recognition, an on-screen keyboard, head-mouse, touch screen and switch input. There is also software available for people who can move a mouse or other pointing device but have difficulty clicking, and alternatives to onscreen keyboard entry.
Overview of Switch Devices
Switch input is way to communicate with your computer that combines an on-screen keyboard with one or more switches positioned anywhere near the user's body where they have reliable movement.
A switch can be of any size or shape, from a big button to a tiny "micro-switch," or even one that is activated by blowing down a tube or by blinking an eye.
The switch (or switches) is used to first select the line and then the column on an on-screen keyboard, which sends that keystroke or command to the program you are using. Switches can also be used to directly operate programs that have been specifically written for switch users.
Even if someone can only use a single switch, they can still effectively operate a computer.
Text Entry Using Dasher
Dasher, a free application developed by the Inference Group at Cambridge University, enables you to use a pointing device to enter text rather than using an on-screen keyboard or ordinary keyboard.
Dasher enables the creation of text by pointing into "predicted" text. It is described as a zooming interface, with the alphabet ranged up on one side (you can customize this if you wish). You point to your letter and zoom in through it to the next likely letter, as shown in fig. 1. The further into the word you get, the more likely it is that all the letters you want will be neatly stacked up. Spaces (white with a line) are offered after each word. Experienced users can create text at 20 words per minute, which is quicker than using an on-screen keyboard.
For further information, see the Dasher Project website.