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The neural mechanisms of auditory distance perception, a function of great biological importance, are poorly understood. Where not overruled by conflicting factors such as echoes or visual input, sound intensity is perceived as conveying distance information. We recorded neuromagnetic responses to amplitude variations over both supratemporal planes, with and without auditory spatial simulations. In the absence of other cues for distance, including those provided by auditory virtual reality, amplitude changes elicited enhanced preattentive responses over the right temporal lobe, indicating hemispheric lateralization of the 'where' pathway in the human. Lesion studies in monkeys and humans have shown that the rostral part of the right superior temporal cortex contributes to spatial awareness in the visual domain. Our data indicate that the distance to a sound source is processed within the adjacent right auditory cortex, thus extending the recent model of a right-hemisphere temporal multisensory matrix that subserves the integration of space-related data across visual and auditory modalities.

For the study of functional organization and reorganization of the human cortex by means of electromagnetic source imaging, a measure of the location and spatial extent of neural sources is of interest. This study evaluates the cortical patch method (CPM), an iterative procedure introduced by Lü tkenhö ner et al. [1995] that models EEG/MEG activity by means of extended cortical patches. Anatomical information is used to constrain estimates of location and extent of neural sources that generate the measured evoked potential. Whereas minimum norm approaches use mathematical constraints to solve the ambiguity of the inverse problem, the CPM introduces constraints based on anatomical and physiological knowledge about neural mass activity. In order to test the proposed method, the simulated activity in an artificial sulcus was subjected to the CPM. The results show that even activity on opposing walls of a sulcus can be well reconstructed. The simulations demonstrate the usefulness and limits of the CPM in estimating the spatial extent of neural sources in the cerebral cortex. As an example, an application of the method on experimental somatosensory evoked potentials is presented in the Appendix.