Dynamic values of the EEG factors in the human perception of sound stimuli

In 43 healthy subjects passing from the state of calm alertness to various conditions of perception of short sounds of different height, interchanging at random, the most expressed is a generalized reduction of individual values of the EEG factor I positively related to the index, mean amplitude and regularity of the alpha-activity and also to mean beta- and theta-amplitudes and negatively related to the theta-index. Maximum reaction by this factor is observed at the beginning of the stimulation; at the second minute of the stimulation, the factor values return towards the initial background level, and again, to a lesser degree, are reduced when carrying out tasks on the sound analysis of stimuli, and the more difficult is the task the stronger is the reduction. In all cases the parietal regions are more reactive than the central ones. By the EEG factor II positively related to the index, frequency and regularity of the beta-activity, the reaction is less expressed and is more local: the factor values in the parietal areas augment only at the beginning of stimulation and diminish at the second minute; and in the central parts, on the contrary, there is a tendency to increase only at the second minute of stimulation. At the sound analysis, reaction is poorly expressed by this factor. Changes of values of the EEG-factor III, positively related to the mean period of the alpha-waves and theta-index, are not great and have only a general tendency to increase at the beginning of the stimulation, and to lower to the background level at the second minute.