In the classic science-fiction movie Forbidden Planet, space travellers from Earth land on a distant world, where they encounter the remnants of a technologically advanced civilisation. Remarkably, the human visitors are able to communicate with one of the alien computers, that is still functioning. Connected through glowing head probes, the men's thoughts and feelings are directly conveyed to the machine over a neural link.
Many similar examples of people having their minds coupled to computers have appeared in other works of fiction. As often depicted, a person simply thinks of a command, and the computer immediately responds--a scheme analogous to the computer voice recognition in use today. Thought recognition would be the ultimate computer interface, the machine acting as an extension of the human nervous system itself.
Electronic circuits can detect the tiny voltage fluctuations on a person's face that arise when the eyes shift in orientation. These impulses are called an electrooculographic signal, or EOG (the name for recordings made of them). EOG signals are used to detect left and right eye motion mapped to left and right cursor motion or on/off switch control.
The electrical signal from muscles is called an electromyographic signal, or EMG. EMGs can control program commands, switch closures, keyboard commands and the functions of the left and right mouse buttons.
The Electro Encephalo Graphic signal describe recordings of voltage fluctuations of the brain that can be detected using electrodes attached to the scalp. These EEG signals arise from the cerebral cortex, a several-centimeter- thick layer of highly convoluted neuronal tissue. The signal is continuous and used for control of cursor vertical or horizontal movement on different signal channels. Most attempts to control a computer with continuous EEG measurements work by monitoring alpha or mu waves, because people can learn to change the amplitude of these two rhythms by making the appropriate mental effort. A person might accomplish this result, for instance, by recalling some strongly stimulating image or by raising his or her level of attention.
(Source: Scientific American 10/96, HUGH S. LUSTED and R. BENJAMIN KNAPP)
Further reading:
The brain-computer interface
Department of Medical Informatics and Ludwig Boltzmann Institute of Medical Informatics and Neuroinformatics Graz