Mismatch negativity evoked by stationary and moving auditory images of different azimuthal positions

The present study has been designed to evaluate the pre-attentive detection of the location changes for stationary and moving sound sources. Auditory event-related potentials to the click trains simulating stationary and moving fused auditory images were recorded from healthy subjects using an oddball paradigm. The spatial characteristics of stimuli were created by introducing constant or variable interaural time delay (ITD) into the click trains. Repetitive standard auditory images (0 or 800 micros ITD, p=0.9) were interspersed by infrequent deviants (p = 0.1) of three types: stationary and moving to or from standards. The deviants moving to standards elicited similar mismatch negativities (MMNs) as compared to the stationary ones. The deviants moving from standards evoked the lowest and latest MMNs depending on standard location. Results suggest that pre-attentive ITD discrimination is essentially dependent on the pattern of ITD changes at the moment of the deviant onset.