An experimental study on EEG characteristics induced by intermittent pure tone stimuli at different frequencies

Exploring the relationships between electroencephalogram (EEG) characteristics and acoustic properties of stimuli can shed some light on how people perceive sound and how sound affects people's emotions. In order to study EEG characteristics induced by sound stimuli with different frequencies, 50 phon and 60 phon intermittent pure tones at the frequency of 125 Hz, 250 Hz, 500 Hz, 1000 Hz and 4000 Hz with a duration of 10 s (a cycle of 1 s, which was divided into four time periods of 0.25 s, the first 0.25 s with sound stimulation, followed by three 0.25 s without sound stimulation) were selected as stimuli. The characteristics of theta, alpha and beta waves in different scalp regions (frontal, temporal, parietal and occipital) of left and right hemispheres were examined. Results of the repeated measures analyses of variance (ANOVA) showed there was a significant main effect of time period on mean theta-wave amplitude in all scalp regions except for the occipital region, which meant there were significant differences among the mean theta-wave amplitudes in four time periods. The asymmetry of alpha wave was found between the left and right temporal regions under stimuli of intermittent pure tones, and the mean alpha-wave amplitude in the left temporal region was significant lower than that in the right temporal region. There was a significant interaction effect among hemisphere, frequency and loudness and a significant main effect of frequency on mean beta-wave amplitude in the parietal region, which turned out that beta wave in the left parietal region was significantly related to the frequencies of pure tone stimuli. The mean beta-wave amplitude in the parietal region under stimuli with same loudness at different frequencies was synergistically influenced by two acoustic parameters (i.e., sharpness and fluctuation strength), and a decreasing trend of mean beta-wave amplitude was observed with the increase of sharpness and fluctuation strength. Besides, the parietal mean beta-wave amplitude under stimuli at 60 phon (within the stimulated 0.25 s) was significantly higher than that at 50 phon.