Preattentive evaluation of multiple perceptual streams in human audition.

To analyze an auditory scene, the segregation of the input into separate streams of information is necessary. Here, the mismatch negativity (MMN) of the event-related potential was used to trace the number of simultaneously monitored streams in auditory scene analysis. Subjects passively listened to sounds belonging to either one, two, or three auditory streams defined by spatial position and pitch. An MMN was obtained for deviants within either one, two or three auditory streams albeit with a smaller amplitude in the latter condition. Control experiments ruled out that this effect was due to variations in stimulation rate. Thus, a preattentive deviant detection system based on simple auditory features provides the basis for subsequent attentive processing directed to a selected stream.