Mechanisms and streams for processing of "what" and "where" in auditory cortex

The functional specialization and hierarchical organization of multiple: ar eas in rhesus monkey auditory cortex were examined with various types of co mplex sounds. Neurons in the lateral belt areas of the superior temporal gy rus were tuned to the best center frequency and bandwidth of band-passed no ise bursts. They were also selective for the rate and direction of linear f requency modulated sweeps. Many neurons showed a preference for a limited n umber of species-specific vocalizations ("monkey calls"). These response se lectivities can be explained by nonlinear spectral and temporal integration mechanisms. In a separate series of experiments, monkey calls were present ed at different spatial locations, and the tuning of lateral belt neurons t o monkey calls and spatial location was determined. Of the three belt areas the anterolateral area shows the highest degree of specificity for monkey calls, whereas neurons in the caudolateral area display the greatest spatia l selectivity. We conclude that the cortical auditory system of primates is divided into at least two processing streams, a spatial stream that origin ates in the caudal part of the superior temporal gyrus and projects to the parietal cortex, and a pattern or object stream originating in the more ant erior portions of the lateral belt. A similar division of labor can be seen in human auditory cortex by using functional neuroimaging.