Auditory Spatial and Object Processing in the Human Planum Temporale: No Evidence for Selectivity

■ Although it is generally acknowledged that at least two pro-cessing streams exist in the primate cortical auditory system, the function of the posterior dorsal stream is a topic of much debate. Recent studies have reported selective activation to auditory spatial change in portions of the human planum tem-porale (PT) relative to nonspatial stimuli such as pitch changes or complex acoustic patterns. However, previous work has suggested that the PT may be sensitive to another kind of non-spatial variable, namely, the number of auditory objects simul-taneously presented in the acoustic signal. The goal of the present fMRI experiment was to assess whether any portion of the PT showed spatial selectivity relative to manipulations of the number of auditory objects presented. Spatially sensitive regions in the PT were defined by comparing activity associated with listening to an auditory object (speech from a single talker) that changed location with one that remained stationary. Activ-ity within these regions was then examined during a nonspatial manipulation: increasing the number of objects (talkers) from one to three. The nonspatial manipulation modulated activity within the “spatial ” PT regions. No region within the PT was found to be selective for spatial or object processing. We sug-gest that previously documented spatial sensitivity in the PT re-flects auditory source separation using spatial cues rather than spatial processing per se.