Handbook of Psychology, Volume 4: Experimental Psychology

Auditory Anatomy and Physiology 125

AUDITORY ANATOMY AND PHYSIOLOGY

The auditory system (see Figure 5.3) has four main parts: The
outer ear collects and funnels sound to the middle ear, which
increases the force produced by air moving the tympanic
membrane (eardrum) so that the fluid and tissues of the inner
ear are efficiently vibrated; this enables the inner ear to trans-
duce vibration into a neural code for sound, which the central
auditory nervous system can process and integrate with other
sensory and experiential information in order to provide
motor, behavioral, and other outputs.

The Peripheral Auditory System: Transduction
and Coding

Outer Ear

As sound travels from the source across the body and head,
especially the pinna (see Figure 5.3), various body parts

attenuate and delay the sound in a frequency-specific way

caused by properties of reflection and diffraction. Thus,

sound arriving at the outer ear canal is spectrally different

from that leaving the source. These spectral alterations are

described by head-related transfer functions (HRTFs), which

specify the spectral (amplitude and phase) changes produced

by the body and head for sources located at different points in

space. The HRTFs may provide cues that are useful for sound

localization (Wightman & Kistler, 1989a). Within the outer

ear canal, resonances can be established that boost sound

pressure in spectral regions near the 3000- to 5000-Hz

resonant frequency of the outer ear canal (Shaw, 1974).

Middle Ear

The major function of the middle ear is to provide an increase

in vibratory force so that the fluids and tissues of the inner ear

can be effectively moved (Geisler, 1998; Pickles, 1988). The

impedance of the inner ear structures is about 40 times greater

Figure 5.3 Cross section of human ear, showing divisions into outer, middle, and inner ears and central nervous

system. Below are listed the predominant modes of operation of each division and its suggested function. Source:

From Yost (2000), adapted from similar drawing by Ades and Engstrom (1974); Dallos (1973), with permission.