The extent to which sound identification and sound localization depend on specialized auditory pathways was examined by using functional magnetic resonance imaging and event-related brain potentials. Participants performed an S1-S2 match-to-sample task in which S1 differed from S2 in its pitch and͞or location. In the pitch task, participants indicated whether S2 was lower, identical, or higher in pitch than S1. In the location task, participants were asked to localize S2 relative to S1 (i.e., leftward, same, or rightward). Relative to location, pitch processing generated greater activation in auditory cortex and the inferior frontal gyrus. Conversely, identifying the location of S2 relative to S1 generated greater activation in posterior temporal cortex, parietal cortex, and the superior frontal sulcus. Differential task-related effects on eventrelated brain potentials (ERPs) were seen in anterior and posterior brain regions beginning at 300 ms poststimulus and lasting for several hundred milliseconds. The converging evidence from two independent measurements of dissociable brain activity during identification and localization of identical stimuli provides strong support for specialized auditory streams in the human brain. These findings are analogous to the ''what'' and ''where'' segregation of visual information processing, and suggest that a similar functional organization exists for processing information from the auditory modality.A uditory scene analysis involves identifying the content (''what'') and the location (''where'') of sounds in the environment. Evidence from anatomical and neurophysiological studies in non-human primates (1-5) suggests that identification and localization of auditory events may be functionally segregated in specialized auditory streams. Combining anatomical and electrophysiological recording methods in non-human primates, Romanski et al. (5) have recently identified two separate auditory streams that originate in caudal and rostral auditory cortex, respectively, and project to different regions within the frontal lobe. The functional significance of these separate pathways has not been determined, although they suggest functional dissociations for auditory processes analogous to the ''what'' and ''where'' or ventral and dorsal cortical information streams for identifying and localizing visual (6, 7) and somatosensory (8) stimuli.Auditory neuroimaging studies employing positron emission tomography or functional magnetic resonance imaging (fMRI) have revealed enhanced blood flow in parietal areas during sound localization (9-11). In comparison, tasks requiring individuals to make tone discriminations (12) or identify auditory stimuli (e.g., words or environmental sounds) show enhanced activation in inferior frontal cortex (13,14). Although these results suggest that the processing of sound identity and sound location is functionally separable, the segregation in auditory information processing has yet to be demonstrated within the same individuals when using the same set of stimu...

The mismatch negativity (MMN) is a frontal negative deflection in the human event-related potential that typically occurs when a repeating auditory stimulus changes in some manner. The MMN can be elicited by many kinds of stimulus change, varying from simple changes in a single stimulus feature to abstract changes in the relationship between stimuli. The main intracerebral sources for the MMN are located in the auditory cortices of the temporal lobe. Since it occurs whether or not stimuli are being attended, the MMN represents an automatic cerebral process for detecting change. The MMN is clinically helpful in terms of demonstrating disordered sensory processing or disordered memory in groups of patients. Improvements in the techniques for measuring the MMN and in the paradigms for eliciting it will be needed before the MMN can become clinically useful as an objective measurement of such disorders in individual patients.

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