To use conventional computer input devices, people need to learn and perform special tasks. They have to be able to handle input devices designed for everyday work and normal physical conditions. The operation of such devices is not intuitive and impossible, or not easily possible, for persons with seriously restricted motor skills. To give these people the chance to use a computer it is necessary to provide them with special input devices. One common way of developing new input devices is to modify conventional tools.
Every person transmits regular biological signals.
Some of them, e.g. eye movement, muscle contraction or speech, may be controlled consciously without training. The computer supported registering of biological signals is a well known aspect of current medical diagnostics. Methods useful for registering eye movement and muscle contraction are optical as well as bio-electrical ones. The bio-electrical method for registration of eye movement exploits the fact that the eye, with retina and cornea, is like an electrical dipole. To record eye movements, two sensor pads are placed above and to the side of one eye to register changes of the electrical potentials.