Human cortical activity related to sound localization in the median plane

Recent studies of sound localization in the horizontal plane have revealed that the right hemisphere is dominant in auditory spatial processing of sounds from different directions. In this study, human cortical activity in response to sound sources located in the median plane was investigated. Auditory stimuli, broad-band noises (100-10,000 Hz), were modified by convolutions with head-related transfer functions (HRTFs) to allow the perception of sound sources outside the head, and were virtually presented from different directions in the median plane. The stimuli were delivered to the ears of subjects using plastic tubes to avoid magnetic interference. Auditory evoked magnetic fields were recorded using a 122-channel whole-head SQUID magnetometer in a magnetically shielded room. Two experiments were conducted with stimuli convolved/unconvolved with HRTFs. Magnetoencephalography (MEG) data obtained from the temporal areas of the left and right hemispheres were chosen and the largest amplitudes of major activity peaks elicited by the auditory stimuli were analyzed. The results showed that the right hemisphere tended to be more sensitive in processing sound sources located in the median plane.