Auditory display for deep brain activation: Hypersonic effect
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We have found that sounds containing high-frequency components above the human audible range (20kHz) significantly increase the regional blood flow in the deep-lying brain structure and the power of the alpha frequency range of the spontaneous electroencephalogram (EEG), and positively affect sound perception. We have termed this phenomenon the ``hypersonic effect'' . To carry out further experiments on this effect, we developed ``Authentic Signal Disc'' that is super audio CD (SACD) software containing the authentic signals for the hypersonic effect and ``Authentic Hypersonic Audio System'' that could reproduce the hypersonic effect. ''Authentic Hypersonic Audio System'' consists of a custom-made SACD player, a de-emphasis controller, filters, two stereo power amplifiers, an output meter unit, and two-way stereo speakers and tweeters. Using these system and disc, we examined recorded EEGs, psychological evaluations based on Scheffe's method, and behavioral evaluations on the optimum listening level, and confirmed the introduction of the hypersonic effect. This system enables us to create some new applications of auditory display.