This is the 2007 version. Click here for the 2017 chapter 04 table of contents.

Summary: The Auditory System

The ear responds to pressure waves in the air gathered by the outer ear and directed down the auditory canal to the tympanic membrane or eardrum. Movements of the eardrum are amplified by a chain of three tiny bones in the middle ear: the ossicles. The cochlea of the inner ear is the part of the auditory system responsible for transduction (conversion of energy from one form to another). The cochlea converts movements of the oval window into standing waves along the cochlear membranes. Hair-like cells along the membranes respond to the movement. They produce nerve impulses that are sent to the brain along the auditory nerve. Normal adults hear frequencies from about 20-20,000 Hz (or, with advancing age, about 50-15,000 Hz).

Sensory hallucinations can be quite vivid and realistic. They occur in all the senses. When people lose normal input to sensory cortex due to accident or old age, the brain tissue may grow irritable and stimulate itself. Normal perception is also a construction like this, but normal perception is constrained and guided by the sensory input, producing results accurate enough to be treated as veridical or faithful to the outside world.


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