Emotion and identification of environmental sounds and electroencephalographic activity

Eight environmental sounds, i.e., playing the harp, cuckoo's song, sound of the waves, cock's crow, noise of the subway, alarm of a clock, sound of a dentist's drill, scratching of the blackboard, and their temporally reverse sounds were presented for 20 sec to 16 college students in a sound-attenuated chamber. The subjects were requested to estimate the degree of pleasantness-unpleasantness and confidence in identifying each sound 10 sec after presentation. Electroencephalography was recorded at C3, C4, O1 and O2 (International 10-20 system), and the mean EEG powers of delta, theta, alpha-1, alpha-2, beta-1 and beta-2 bands during the sound presentations were computed by a signal processor. The results were as follows: 1) Even when the loudness and frequency component of the sounds were equivalent, there was big difference in pleasantness-unpleasantness estimation among the environmental sounds. 2) Inaccuracy in identifying the sounds presented backwards neutralized the pleasantness-unpleasantness estimation. 3) Powers of theta and low frequency alpha bands were higher during presentation of the pleasant sounds than during presentation of the unpleasant sounds. 4) Alpha activity was more closely related with subjective confidence in sound identification than with pleasantness-unpleasantness estimation of sound. These findings suggest that pleasantness-unpleasantness estimation of environmental sounds depends not only on their loudness level or frequency component but on the accuracy in sound identification and that modification of sound identification may be useful in alleviating the environment noise problem. Alpha activity seems to be closely related to the recognition of sound, but further research is needed on EEG activity in the relationship between the emotional state and sound identification.