Adaptation to shifted interaural time differences changes encoding of sound location in human auditory cortex.

The auditory system infers the location of sound sources from the processing of different acoustic cues. These cues change during development and when assistive hearing devices are worn. Previous studies have found behavioral recalibration to modified localization cues in human adults, but very little is known about the neural correlates and mechanisms of this plasticity. We equipped participants with digital devices, worn in the ear canal that allowed us to delay sound input to one ear, and thus modify interaural time differences, a major cue for horizontal sound localization. Participants wore the digital earplugs continuously for nine days while engaged in day-to-day activities. Daily psychoacoustical testing showed rapid recalibration to the manipulation and confirmed that adults can adapt to shifted interaural time differences in their daily multisensory environment. High-resolution functional MRI scans performed before and after recalibration showed that recalibration was accompanied by changes in hemispheric lateralization of auditory cortex activity. These changes corresponded to a shift in spatial coding of sound direction comparable to the observed behavioral recalibration. Fitting the imaging results with a model of auditory spatial processing also revealed small shifts in voxel-wise spatial tuning within each hemisphere.