**7. Deficiencies of the existing models of the OHC and whole cochlea**

So far the existing models (theories) of the amplification in a single outer hair cell (OHC) and the entire cochlea do not take into account all the physical phenomena experimentally observed. They are phenomenological theories, not related to actual physical (physiological) processes occurring in a single OHC and in the entire inner ear. In recent years a theory has gained popu‐ larity, which attributed the phenomenon of the cochlear amplification to Hopf bifurcations [21]. This theory, however, raised many doubts among others concerning the problem of stability [22]. Many authors of papers published very recently stated that in the theory of the cochlear amplification many unresolved problems still exist and work on it must be continued [14, 23–27].

A similar discussion applies considering electronic models of a single OHC and the entire cochlea. These models to a greater or lesser extent, describe the characteristics of a single OHC and the whole cochlea, but do not reflect their physical structure.

In conclusion, one can state that none of the existing theories of hearing explains satisfactorily the mechanism of the signal processing phenomena occurring in the cochlea.
