PHASE COHERENCE OF THE SLOW BRAIN OSCILLATIONS AS AN INDEX OF PREATTENTIVE SOUND DISCRIMINATION
The aim of the present study was to investigate the effect of dynamic characteristics and context roles of the sound stimuli on the evoked rhythmic activity of the human brain. The signals differed in their temporal ITD patterns so as to simulate either stationary sounds or stepwise auditory motion. The reversed oddball stimulation was used to present both stimulus types as standards and deviants in different blocks. The event-related spectral perturbation (ERSP) and inter-trial phase coherence (ITC) were calculated from the time-frequency decomposition of EEG signals. The abrupt displacement of the standard stimulus increased the ITC in the alpha range and to a lesser extent in the theta range, compared to the stationary standard. When the moving stimuli were used as deviants, the differences in the coherence of the evoked oscillations increased. The deviance detection was accompanied by synchronization of slow oscillations in the direct oddball sequence and by their desynchronization in the reversed sequence. Our results suggest that phase coherence of slow oscillations may be considered as neural correlate of the preattentive discrimination of sound motion.