Eric Javel
Div. of Otolaryngol., Duke Univ. Med. Ctr., Durham, NC 27710
Cat auditory-nerve fiber tuning curves were fitted by a three-process model consisting of an acoustic resonance (for tuning curve ``tails''), a skewed function formed by subtracting two exponentials (for basilar membrane resonances), and a Gaussian function (for the active gain responsible for sharp tuning). Thresholds were taken as the sum of pressures provided by the two resonances, multiplicatively enhanced in a spatially dependent manner by the active gain. Fits were generally excellent. ``Tails'' possessed center frequencies (1--3 kHz) and minima (60--80 dB SPL) that varied from animal to animal and depended on fiber CF. Basilar membrane resonances possessed average minima of 30--50 dB SPL in low-threshold fibers, tuning that increased in sharpness with CF or threshold, and center frequencies that were typically lower (for CFs >1 kHz) or higher (for CFs <1 kHz) than the center frequencies of the associated active gains. Average active gain magnitude in low-threshold fibers increased smoothly from <10 dB in low-CF fibers to >40 dB in high-CF fibers, and was reduced or absent in most high-threshold fibers. The average spatial extent of the active gain was remarkably constant at 1 mm regardless of gain magnitude, fiber CF, or threshold sensitivity. [Work supported by NIDCD.]