Automatic and intrinsic auditory "what" and "where" processing in humans revealed by electrical neuroimaging.

The auditory system includes 2 parallel functional pathways-one for treating sounds' identities and another for their spatial attributes (so-called "what" and "where" pathways). We examined the spatiotemporal mechanisms along auditory "what" and "where" pathways and whether they are automatically engaged in differentially processing spatial and pitch information of identical stimuli. Electrical neuroimaging of auditory evoked potentials (i.e., statistical analyses of waveforms, field strength, topographies, and source estimations) was applied to a passive "oddball" paradigm comprising 2 varieties of blocks of trials. On "what" blocks, band-pass-filtered noises varied in pitch, independently of perceived location. On "where" blocks, the identical stimuli varied in perceived location independently of pitch. Beginning 100 ms poststimulus, the electric field topography significantly differed between conditions, indicative of the automatic recruitment of distinct intracranial generators. A distributed linear inverse solution and statistical analysis thereof revealed activations within superior temporal cortex and prefrontal cortex bilaterally that were common for both conditions, as well as regions within the right temporoparietal cortices that were selective for the "where" condition. These findings support models of automatic and intrinsic parallel processing of auditory information, such that segregated processing of spatial and pitch features may be an organizing principle of auditory function.