抄録
A system (Fig.1) has been constructed, which is able to feedback to the subject information about the difference between short-term average amplitude or frequency of his alpha waves and a certain preset reference level. The property of feedback control of human alpha activity was examined by this means. First, occipital EEG of the subject was filtered by 8-13 Hz band pass filter and the amplitude or the number of zero-crossing points for a past short interval (routinely 4 sec) were calculated by a special counter circuit. The output of the counter was compared with a reference level and the difference was converted into an auditory signal (characteristics of the converter is indicated in Fig.2) and indicated for each 0.5 sec to the subject.
Using the above system a feedback learning experiment was performed on normal adults in their three states-eyes closed, eyes half-opened and eyes opened. The results (Fig.4 and 6) were as follows : (1) Subjects were capable of controlling the alpha amplitude in the range between their resting, closed eyes-level to opened eyes-level. In controlling the alpha frequency the range was 9. 5 to 11. 5 Hz. (2) State with the eyes half-open showed widest range of control of both amplitude and frequency.
Discussions were made on the possible improvement of feedback signalling and on the strategies used by the subjects.
