‘‘What’’ and ‘‘where’’ in the auditory cortex

Abstract

Several cortical fields have been defined in the superior temporal gyrus (STG) of the rhesus monkey. These ‘‘belt’’ areas are further characterized by their responses to spatially localized, species-specific vocalizations. Neurons in the caudal belt are more specific for spatial location, whereas neurons in the rostral belt are more selective for communication calls. Furthermore, the caudal and rostral belt project to distinct regions of the prefrontal cortex previously identified as subserving roles in visual spatial analysis and object recognition, respectively. Functional neuroimaging in humans also supports the existence of dual streams for the processing of sound content and location. Complex sounds generally activate a larger area in the belt region of the STG than tones. Consonant–vowel combinations give rise to activity distributions anterior to Heschls gyrus, which are organized into ‘‘phonetic maps.’’ If visual input is added in a McGurk-type fusion experiment, these maps are found to shift in individual subjects. Virtual auditory space stimuli administered via headphones activate two regions in the posterior parietal cortex. When this activation is compared with that by a visual spatial task, no overlap is found in the inferior parietal cortex, whereas convergent input is present in a superior parietal region.