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Hearing, technically known as audition.
Audition depends upon
I) the ear- outer, middle, and inner- which responds to sounds in
the air,
2) the auditory nerve, which is stimulated by the action of the
ear; and
3) certain parts of the brain, in which impulses transmitted via
the auditory nerve produce awareness of the original sound stimulus.
Sounds may originate from any one of a number of sources, such as
a violin string that has been bowed, the column of air pulsating
in an organ pipe, or the vocal cords of a person speaking.
The motion of each of these sources disturbs the surrounding air,
first minutely compressing and then minutely decompressing it.
From each source, consequently, there emanates a series of high-pressure
and low-pressure waves that progresses rapidly through the air.
Such a moving train of waves constitutes a sound, the stimulus to
audition.
Most of the sounds encountered in everyday life are very complex.
Their sources execute very complicated movements, and the sound
waves themselves are correspondingly complex.
In experiments with audition the sound stimulus is usually made
as simple as possible in order to clarify the experimental results.
A great deal of care is taken to be sure that the sound source vibrates
with the simple sinusoidal motion of a pendulum.
The resulting train of sound waves, called a pure tone, shows a
smooth, regular variation between high and low pressures.
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