[ACTIVE AND PASSIVE DISCRIMINATION OF MOVING SOUNDS: RHYTHMIC ACTIVITY OF HUMAN BRAIN]

The spectral dynamics of the EEG rhythmicity during active and passive discrimination of stationary and moving sound stimuli presented according to the oddball paradigm were investigated. Standard stimuli represented stationary midline sounds. Deviant stimuli simulated smooth and stepwise sound source motion (to the left/right from head midline) produced by linear and stepwise changes of interaural time delay. Significant changes of the brain oscillations were found in the frequency range of 3-30 Hz. The dynamics of the moving deviant stimuli (smooth vs. stepwise) had greater impact on theta-rhythm power in active listening conditions: a stronger theta-power increase was evoked by the stepwise sound motion as compared to smooth motion. Significant increase in theta-power was also observed with rightward sound displacement as compared to leftward displacements. Active deviant discrimination reduced alpha-power (8-11 Hz) mostly during smooth deviant motion. The power increase of lower alpha-oscillations (12-15 Hz) was stronger with step- wise motion than with smooth motion of deviants. The interhemispheric asymmetry of beta-power decrease in active conditions (as compared to passive) was found in the whole beta-range. The sup- pression of beta-power was stronger at the right hemisphere than at the midline or left hemisphere and showed no dependence on spatial properties of the deviant stimuli. This asymmetry may be related to selective attention to task-relevant sounds and with preparation to motor response. Generally, active auditory discrimination resulted in stronger deviant-related changes of the wide-ranged EEG spectral power than passive discrimination with attentional tuning to task-irrelevant stimuli.