Psychophysiological effects of unperceivable stimuli

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This study was conducted to clarify the psychophysiological effects of unperceivable stimuli on human, especially the effects of ultrasonic sound on EEG. Experimental procedures and results obtained are as follows ;(1) Apparatus : Auditory stimuli were generated by a function generator (Iwatsu, FG350) utilizing PC-9801 DA microcomputer (NEC) and D/A converter installed in it Output from the function generator was amplified by an audio amplifier (DENON PMA390). Auditory stimuli were presented to the subuject through a headphone (PANASONIC RP-Fl). EEG was recorded by the Electroencephalography (Nihon-kohden EEG-7314). Recorded data were stored on the magnetic tape by a cassette data recorder (TEAC R-61).(2) Auditory stimulus presentation : Three kinds of auditory stimuli (200 Hz, 2 Khz and 20 KHz sine wave) were presented in a random order. Duration of the presentation was between 25 and 35 sec (mean = 30 see). ITI was also between 25 and 35 sec (mean = 30 sec). Amplitude of each auditory stimulus raised in a form of sinusoid curve reaching its peak within 200 ms after the trigger signal onset. At the offset of the stimulus, the amplitude falled also in a form of sinusoid curve reaching 0 point within 200 msec.(3) Procedure : The subject was seated with his eyes closed on a reclining chair in a partly sound proof - electromagnetic shielded room. Ag/AgCl electrodes were attached to F3, C3, 01 and A2 (reference) points for recording EEG. Horizontal and vertical EOG and ECG were also recorded for cheeking their possible contamination in EEG records.(4) EEG data analysis : Recoded EEG amplitude data from C3 point were digitized in 12 bit everly 10 msec. FFT was performed on these digitized data. It was found that components of 7-8 Hz (slow alpha) and 6-7 Hz (fast rheta) increased as the ultrasonic sound of 20 Khz was presented. Further study in now in pregress, by increasing the number of subjects and adding several control paradigms.