Basilar-membrane resonance peaks shift downward as input level rises

Evidence

The characteristic frequency is defined as that frequency for which the frequency response reaches ib; highest local maximum at low input levels. The peak shifts towards lower frequencies at high input levels. The general characteristic of the frequency response is of a low-pass shape, as expected. The low-frequency slope is relatively shallow, whereas the high-frequency slope is rather steep. At lower levels, the frequency response is much more strongly peaked than at high levels, and shows several maxima due to the irregularities of the model elements. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 357