The auditory periphery is non-linear and cannot be captured by one transfer function.

Evidence

The rate at which the action potentials occur is often called the firing rate. A tiny recording electrode can be surgically placed in the proximity of the nerve. Neural responses in the auditory nerve fibres can be registered for different stimulus signals sent to the ear, and thus the whole chain of peripheral hearing can be investigated experimentally. Since the system is not linear and time-invariant (LTI), no single transfer function can represent it, but many points of view must be studied and characterized with different input–output relationships. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 783

Categorization

• DEFINE: Defines firing rate and explains why hearing cannot be modeled as an LTI system.