“What” and “where” in the human auditory system

Abstract

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 and/or 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 event-related 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.