Monita Chatterjee
Jozef J. Zwislocki
Inst. for Sensory Res., Syracuse Univ., Syracuse, NY 13244
Rate intensity (RI) functions of afferent auditory-nerve fibers of mammals are known to depend on frequency deviations from the fibers' best frequencies (BFs) and also on their BF thresholds. The functions become flatter as either the frequency is increased from below BF to above BF or the fibers' thresholds increase. In the latter case, the functions cover an extended range of SPLs. It is shown empirically that both relationships can be accounted for by two kinds of nonlinearity found in the alternating receptor potentials of the hair cells, in particular, inner hair cells (IHCs), one producing amplitude compression, the other, a lowering of BF as SPL is increased. Past models of fiber RI functions seem to have relied on the first nonlinearity. The second nonlinearity suggests that, at a given cochlear location, fibers with relatively high thresholds have lower BFs than fibers with relatively low thresholds, and that the hard saturation of the latters' RI functions may have a cochlear origin. [Work supported by NIDCD and DiCarlo Fellowship.]