Fig. 1.

The factors underlying the steepness of auditory-nerve (AN) rate versus level functions, taken from Heinz and Young (2004). The first box shows basilar membrane (BM) velocity plotted versus sound level in normal (n) and impaired (i) ears (Ruggero and Rich 1991). The differences are due to loss of cochlear amplification and compression due to outer hair cell (OHC) damage. The central box shows a plot of inner hair cell (IHC) response versus BM motion for normal ears and for those with IHC damage (h). The third box shows AN rate functions in normal and impaired ears. The solid lines are for low threshold (high spontaneous rate, SR) fibers, and the dashed lines are for high threshold (low and medium SR) fibers. Cases with OHC impairment only (i) show steeper rate functions in the low SR fibers because of the change in slope of the BM response. Cases with OHC and IHC impairment (h) show a reduced slope because of the reduced output of IHCs.