Event-Related Potentials in Conditions of Auditory Spatial Masking in Humans

Current study is focused on human event-related potentials (ERPs) elicited in the auditory spatial masking paradigm. ERPs of the test subjects ( n = 18) were recorded in the passive conditions using uncorrelated low-frequency noise signals. Spatial positions of the stimuli were determined by interaural level differences (ILDs). Test signal and masker were colocated or separated by 90 or 180 deg of azimuth and were presented simultaneously. The onset of a test signal was delayed from masker onset in order to separate the onset responses. We estimated the ERPs dependence on angular distance between signal and masker. When the test signal was presented against the background of a masker, the N1 and P2 components decreased in magnitude and increased in latency, as compared to presentation in silence. Spatial release from masking resulted in ERP magnitude increase and latency decrease as the angular distance between test signal and masker changed from 0 to 90 deg. A further spatial separation of the lateralized signal and masker did not result in further release from masking. ERPs magnitude was a more reliable indicator of the angular separation of signals than its latency. These findings suggest that binaural unmasking mechanisms operate at the preconscious stage of complex auditory scene analysis.