2010 Volume 22 Issue 3 Pages 96-104
The paper investigated amplitude change of electroencephalogram during performing mental task and listening to unpleasant/pleasant sound in order to evaluate effects of mental work and acoustic environment on brain electrical activity. The amplitude of the alpha wave was decreased by approximately 15∼20% during performing the mental task (mental arithmetic and memorization) and/or listening to acoustic stimuli (5KHz tone and classical music Pachelbel's Canon) in comparing to the amplitude of the alpha wave at rest. Such amplitude suppression corresponds to increase of temporal phase fluctuation of the alpha wave by 15∼30%. In particular, the reduction rate of the amplitude of the alpha wave in the low-frequency range was up to 25% under the combined stresses, namely, the mental arithmetic and unpleasant 5KHz tone, whereas it was limited to 15∼20% during performing the mental arithmetic alone and listening to 5KHz tone alone. On the other hand, the amplitude of the beta and gamma waves showed no significant change under most of stress conditions. The result suggests that the sound and mental stresses suppress the alpha wave in the low frequency range which should be taken into account in the measurement of mental stress.