Shared cortical systems for processing of horizontal and vertical sound motion.

Cortical processing of horizontal and vertical sound motion in free-field space was investigated using high-density electroencephalography in combination with standardized low-resolution brain electromagnetic tomography (sLORETA). Eighteen subjects heard sound stimuli that, after an initial stationary phase in a central position, started to move centrifugally, either to the left, to the right, upward, or downward. The delayed onset of both horizontal and vertical motion elicited a specific motion-onset response (MOR), resulting in widely distributed activations, with prominent maxima in primary and nonprimary auditory cortices, insula, and parietal lobe. The comparison of MORs to horizontal and vertical motion orientations did not indicate any significant differences in latency or topography. Contrasting the sLORETA solutions for the two motion orientations revealed only marginal activation in postcentral gyrus. These data are consistent with the notion that azimuth and elevation components of dynamic auditory spatial information are processed in common, rather than separate, cortical substrates. Furthermore, the findings support the assumption that the MOR originates at a stage of auditory analysis after the different spatial cues (interaural and monaural spectral cues) have been integrated into a unified space code.