ABSTRACT
Behavioral and physiological studies implicate auditory cortex as playing a pivotal role in spatial hearing. Here we describe a new approach to simulation of free-field sound sources and its application to studies of neural mecha nisms of spatial hearing. We synthesized a set of signals (clicks) for earphone delivery whose waveforms and amplitude spectra, measured at the eardrum, mimic those of sounds arriving from a free-field source. A full array of these signals forms a “virtual acoustic space.” Primary auditory cortical neurons exhibit “virtual space receptive fields” (VSRFs) similar to those obtained under open-field conditions. VSRFs of Al cells can be placed into five categories based on size and location at stimulus levels 20-30 dB above threshold. VSRFs are shaped, in part, by binaural interactions. These fields are not homogeneous throughout with respect to discharge strength or spike timing. For certain cells a restricted region in virtual acoustic space exists for which latency is shortest and firing level is highest. This is referred to as the "effective virtual space receptive field” and is interpreted as a focus of activity that may signal stimulus direction. Simulated linear movement of a sound source revealed that some cells are motion sensitive.
