Right-hemisphere dominance for the processing of sound-source lateralization

Cortical processing of change in direction of a perceived sound source was investigated in 12 human subjects using whole-head magnetoencephalography. The German word "da" was presented either with or without 0.7 msec interaur al time delays to create the impression of right- or left-lateralized or mi dline sources, respectively. Midline stimuli served as standards, and later alized stimuli served as deviants in a mismatch paradigm. Two symmetrically linked dipoles fitted to the mismatch fields showed stronger moments in th e hemisphere contralateral to the side of the deviant. The right dipole dis played equal latencies to both left and right deviants, whereas left dipole latencies were longer for ipsilateral than contralateral deviants. Frequen cy analysis between 20-70 Hz and statistical probability mapping revealed i ncreased induced gamma-band activity at 53 +/- 2.5 Hz to both types of devi ants. Right deviants elicited spectral amplitude enhancements in this frequ ency range, peaking at latencies of 160 and 240 msec. These effects were lo calized bilaterally over the angular gyri and posterior temporal regions. C oherence analysis suggested the existence of two separate interhemispheric networks. For left-lateralized deviants, both spectral amplitude enhancemen ts at 110 and 220 msec and coherence increases were restricted to the right hemisphere. In conclusion, both mismatch dipole latencies at the supratemp oral plane and gamma-band activity in posterior parietotemporal areas sugge sted a right hemisphere engagement in the processing of bidirectional sound -source shifts. In contrast, left-hemisphere regions responded predominantl y to contralateral events. These findings may help to elucidate phenomena s uch as unilateral auditory neglect.