Discrimination of Moving Sound Stimuli: Spectral Characteristics of Human Brain Activity

The aim of the present work was to compare EEG spectral characteristics as subjects discriminated stationary and moving sound stimuli in active (paying attention to the stimulus) and passive (not paying attention) listening using an oddball paradigm. The standard signal was a sound signal modeling the action of a stationary sound source located at the midline of the head. Deviant stimuli consisted of two types of moving stimulus with smooth and stepwise movements. Signifi cant changes in EEG spectral power were found in the range 3–30 Hz. The effects of deviant stimulus movement dynamics on the power of θ oscillations (3–7 Hz) were more marked in conditions of active discrimination: the increase in power was greater for stepwise movement of deviant stimuli than for smooth movement and also on movement of the stimulus to the right. Suppression of α rhythms (8–11 Hz) was seen in the active listening task, this being most marked on smooth movement of deviant stimuli. An increase in power in the lower subrange of the β rhythms (12–15 Hz) was greater for stepwise movement than smooth movement of deviants. Interhemisphere asymmetry in the extent of suppression of power in active conditions as compared with passive was seen throughout the β range. Suppression was greater in the right hemisphere than at the midline of the head or in the left hemisphere. Interhemisphere asymmetry of β rhythms was independent of the spatial properties of the stimuli. The presence of hemisphere asymmetry may be associated with paying attention to the task performed and the formation of the motor response. Overall, for all frequency ranges studied, the dynamics of stimulus movement had greater infl uences on EEG spectral power in conditions of active discrimination than in passive conditions.