VIRTUAL-SPACE RECEPTIVE-FIELDS OF SINGLE AUDITORY-NERVE FIBERS

1. Sounds reaching the tympanic membranes are first modified by the ac oustic properties of the torso, head, and external ear. For certain fr equencies in the incident sound there results a complex, direction-dep endent spatial distribution of sound pressure at the eardrum such that , within a sound field, localized areas of pressure maxima are flanked by areas of pressure minima. Listeners may use these spatial maxima a nd minima in localizing the source of a sound in space. The results pr esented describe how information about this spatial pressure pattern i s transmitted from the cochlea to the central auditory system via sing le fibers of the auditory nerve. 2. Discharges of single fibers of the auditory nerve were studied in Nembutal-anesthetized cats [characteri stic frequencies (CFs) ranged from 0.4 to 40 kHz]. Click stimuli were derived from sound-pressure waveforms that were generated by a loudspe aker placed at 1,800 locations around the cat's head and recorded at t he tympanic membrane with miniature microphones. Recorded signals were converted to acoustic stimuli and delivered to the ear via a calibrat ed and sealed earphone. The full complement of signals is referred to as ''virtual acoustic space,'' and the spatial distribution of dischar ges to this array of signals is referred to as a ''virtual-space recep tive field'' (VSRF). 3. Fibers detect both pressure maxima and pressur e minima in virtual acoustic space. Thus VSRFs take on complex shapes. 4. VSRFs of fibers of the same or similar CF having low spontaneous r ates had the same overall pattern as those from high-spontaneous rate (HSR) fibers. For HSR fibers, the VSRF is obscured by the high backgro und spike activity. 5. Comparison of the VSRF and isolevel contour map s of the stimulus derived at various frequencies revealed that auditor y nerve fibers most accurately extract spectral information contained in the stimulus at a frequency close to or slightly higher than CF.