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Abstract
<p class="first" id="d9090655e59">This paper describes the development and testing
of a system whereby one can communicate
through a computer by using the P300 component of the event-related brain potential
(ERP). Such a system may be used as a communication aid by individuals who cannot
use any motor system for communication (e.g., 'locked-in' patients). The 26 letters
of the alphabet, together with several other symbols and commands, are displayed on
a computer screen which serves as the keyboard or prosthetic device. The subject focuses
attention successively on the characters he wishes to communicate. The computer detects
the chosen character on-line and in real time. This detection is achieved by repeatedly
flashing rows and columns of the matrix. When the elements containing the chosen character
are flashed, a P300 is elicited, and it is this P300 that is detected by the computer.
We report an analysis of the operating characteristics of the system when used with
normal volunteers, who took part in 2 experimental sessions. In the first session
(the pilot study/training session) subjects attempted to spell a word and convey it
to a voice synthesizer for production. In the second session (the analysis of the
operating characteristics of the system) subjects were required simply to attend to
individual letters of a word for a specific number of trials while data were recorded
for off-line analysis. The analyses suggest that this communication channel can be
operated accurately at the rate of 0.20 bits/sec. In other words, under the conditions
we used, subjects can communicate 12.0 bits, or 2.3 characters, per min.
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