Outer hair cell damage explains recruitment by disabling active cochlear gain

Evidence

The effect of recruitment can be illustrated using the nonlinear-activefeedback model of peripheral signal processing. The assumption is that noiseinduced hearing loss starts with the outer haircells being impaired, so that they fail in what has been described as active processing. This seems to be a reasonable assumption, although we may also have to consider impairment in the inner haircells at more severe stages of hearing loss. With the outer haircells’ activity switched off, i.e. the preprocessing model being totally passive, the level at the characteristic place of the tone exciting the model rises in the same way as the level that is put into the model. This effect is shown by the 45°-line (solid) in Fig. 16.34a. With the outer haircells active, this relationship changes drastically so that at lower levels of the input voltage, much higher levels at the characteristic place are found. The difference may reach 40 dB Fig. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1961

Categorization

• XREF: Connects to the nonlinear-active-feedback cochlear model and outer hair cell compressive gain familiar from auditory neuroscience literature.
• QUESTION: The degree to which inner hair cell impairment contributes at more severe stages of hearing loss is acknowledged but unresolved here.