Spatial processing in the auditory cortex for stream segregation and localization

The further apart two sounds are along the horizontal azimuth, the more likely they are to be heard as two separate sources. This spatial stream segregation (SSS) function may be dissociable from that of locating sound sources, but most neuroscience research on spatial hearing has focussed on the latter. Such research has uncovered spatial-sensitivity in the posterior auditory cortex, which has correspondingly been characterized as part of the "where" processing pathway for localization. However, other evidence indicates that this spatial sensitivity may be more relevant for SSS than for localization. We tested this hypothesis using 7 tesla functional magnetic resonance imaging. We measured brain activity in ten, normal-hearing adults while they listened to two concurrent auditory streams, spatially-separated along the horizontal azimuth. We applied multivoxel pattern classifiers to decode brain activity patterns associated with changes in location that resulted in either altered or constant SSS. We reasoned that if spatially-sensitive auditory cortex is optimized for SSS, then changes in spatial separation will be better decoded than mere changes in location. Our hypothesis was supported in the hemisphere contralateral to the sound locations. This result supports that spatial sensitivity in the auditory cortex is optimized for scene analysis rather than localization.