Chapter 4

Chapter summary

A complex sound wave can be regarded as a collection of many simple sine waves at different frequencies (Fourier theory). The human auditory system acts as a filter which removes some of these frequency components and preserves others. The peripheral auditory system includes the outer ear, middle ear, and inner ear (cochlea). Hair cells at different places in the cochlea encode different sound frequencies (frequency-to-place conversion). The central auditory system includes several populations of cells in the brainstem and cerebral cortex which receive signals from the cochlea.

The "what" attributes of a sound (its frequency composition and temporal structure) are encoded by neurons in the auditory system, distributed according to their preferred sound frequency (tonotopic organisation).

The "where" attributes of sound (the location of the sound source in auditory space) are encoded by binaural cells which receive inputs from both ears. Some binaural cells are sensitive to tiny differences in the time that a sound arrives at one ear relative to the other (inter-aural time difference or ITD), and other cells are sensitive to intensity level differences between the sound signals arriving at the ears (inter-aural level difference or ILD).