The sharp frequency selectivity of low- and medium- spontaneous rate auditory nerve fibers might allow for rate-place coding up to 5 kilohertz

Abstract

One feature that might differentiate the three types of spontaneous rate (SR) auditory nerve fibers (ANFs) is the sharpness of frequency tuning at comparable sound pressure levels. My hypothesis, prior to modeling the tuning curves for each fiber type, was that low-SR fibers have a higher threshold for stimulation and thus have sharper frequency selectivity than medium-SR fibers, which in turn have sharper frequency selectivity than high-SR fibers. The results of the simulation support this framework. I used the Zilany et al. (2014) model of the auditory periphery and the cochlear tuning parameters from Shera et al. (2002) to generate tuning curves and neurogram raster plots for each of the three fiber types. The results of the simulation suggest that the sharp frequency selectivity of low-SR and medium-SR ANFs might allow for resolved rate-place coding up to 5 kHz. At frequencies below 1500 Hz, high-SR fibers were seen to have very different response properties than low-SR and medium-SR fibers. It is conceivable that the different fiber types constitute parallel pathways and mediate two different coding schemes. We should consider whether these sharply tuned low-SR and medium-SR ANFs, while fewer in number than High-SR ANFs, might be especially important for rate-place frequency coding.