Outer and middle ear act linearly while inner-ear mechanics are nonlinear

Evidence

The outer ear and the middle ear are ignored in the model and it is assumed that they do not produce nonlinear effects. They can therefore be treated as linear circuits, the frequency and phase response of which can easily be added at the input of the model. The hydromechanics of the inner ear and the behaviour of the outer haircells, hmvevcr, playa crucial role and are responsible for the frequency-place transformation. The approximation of the complicated hydromechanic system by a one-dimensional model is rough but effective. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 344

Categorization

• QUESTION: Is the linearity assumption for outer/middle ear well-established or an approximation the model simply adopts?