Abstract
Brain alpha wave responses to unpleasant and pleasant sounds are investigated in terms of the amplitude and phase. The amplitude of the alpha wave is significantly reduced during listening to the unpleasant sounds, e. g., teeth gnashing and a single frequency tone with a frequency of 5 KHz as well as listening to the pleasant sounds, e. g., Pachelbel's Canon and babble of a stream. Such amplitude instability is found to be prolonged at least for 100 s after listening to the sounds. Moreover, temporal phase change rate of the alpha wave is increased during and after listening to the unpleasant sounds, whereas it is not significantly increased for the pleasant sound. The effects of the unpleasant sounds on the alpha wave seem to remain in the brain electrical activity for a longer period.
