[Studies on the activity level of the cerebral cortex by the noise exposure -- with regard to the function of maintaining concentration (TAF) and average auditory evoked response (AER) (author's transl)].

Subjects were exposured to two qualitatively different kind of noise (white noise and variable noise) with the same sound pressure of 90 phon for one hour as the mental stress. Changes of the function of maintaining concentration (TAF), flicker fusion (Ff), EEG and average auditory evoked response (AER) caused by this noise exposure were analyzed. The results obtained are as follows: 1) TAF-L and TAF-D of the white noise group after the exposure significantly lowered in comparison with the values before exposure, whereas in the variable noise group they tended to lower after the exposure. 2) FF of the both noise group significantly lowered after the exposure. 3) The difference in EEG before and after exposure was greater in the white noise group than in the variable noise group. 4) In analysis of variance on each frequency band of EEG during the exposure by group, a significant difference was observed between the two groups and it was noted that the exposure to white noise greatly affected the EEG. 5) The difference in N1 latency of AER before and after the exposure was greater in the white noise group than in the variable noise group. 6) In the white noise group, a significant correlation was observed between the lowering of TAF-L and the delay of N1 latency of AER. The present study on EEG and AER is further evidence of the accuracy of the function of maintaining concentration (TAF) in measuring the mental stress.