[Communication device utilizing event-related potentials]

We had developed a communication system using a theory of P300 through a computer. 17 healthy subjects participated in all 3 experiments, while 4 ALS and 1 OPCA patients took part in the first 2 experiments only. In the 1st experiment, 4 short sentences of 'yes very much', 'yes' 'no' and 'can't answer' were shown on the display. The subjects were asked to select one of them as target. During the experiment 1, color of background was randomly changed for each sentence as the stimulation for the period of 300 msec and the interstimulus interval was 1,500 msec. In the 2nd experiment, 46 letters of Japanese character and several symbols were shown on the display (5 columns x 10 rows). In the 3rd experiment, we used 16 pictures together with X (4 columns x 5 rows). During recordings, the color of background was randomly changed for each row and then for each letter/picture of column containing target in experiment 2 as well as in experiment 3. The subjects were asked to start counting and when the target was stimulated, they were instructed to stop the counting process and repeat counting again until they encountered the stimulation of target again. This was repeated for the entire recordings. Computer defined a target by a biggest positive voltage between 300 and 600 msec and/or by the most powerful spectrum in 2-5 Hz after Fast Fourier transform in an averaged P300 (averaging number = 5-7). We then calculated the percentage of correct target by comparing the result and actual target. Results indicate that this communication aids can be used conveniently in patients with severe motor disabilities.