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The place theory of hearing proposes that different areas of the cochlea respond to different
frequencies. Higher tones excite areas closest to the opening of the cochlea (near the oval
window). Lower tones excite areas near the narrow tip of the cochlea, at the opposite end. Pitch
is therefore determined in part by the area of the cochlea firing the most frequently.
Just as having two eyes in slightly different positions allows us to perceive depth, so the fact that
the ears are placed on either side of the head enables us to benefit from stereophonic, or three-
dimensional, hearing. If a sound occurs on your left side, the left ear will receive the sound
slightly sooner than the right ear, and the sound it receives will be more intense, allowing you to
quickly determine the location of the sound. Although the distance between our two ears is only
about 6 inches, and sound waves travel at 750 miles an hour, the time and intensity differences
are easily detected (Middlebrooks & Green, 1991). [2] When a sound is equidistant from both
ears, such as when it is directly in front, behind, beneath or overhead, we have more difficulty
pinpointing its location. It is for this reason that dogs (and people, too) tend to cock their heads
when trying to pinpoint a sound, so that the ears receive slightly different signals.
Hearing Loss
More than 31 million Americans suffer from some kind of hearing impairment (Kochkin,
2005). [3] Conductive hearing loss is caused by physical damage to the ear (such as to the
eardrums or ossicles) that reduce the ability of the ear to transfer vibrations from the outer ear to
the inner ear. Sensorineural hearing loss, which is caused by damage to the cilia or to the
auditory nerve, is less common overall but frequently occurs with age (Tennesen, 2007). [4] The
cilia are extremely fragile, and by the time we are 65 years old, we will have lost 40% of them,
particularly those that respond to high-pitched sounds (Chisolm, Willott, & Lister, 2003). [5]
Prolonged exposure to loud sounds will eventually create sensorineural hearing loss as the cilia
are damaged by the noise. People who constantly operate noisy machinery without using
appropriate ear protection are at high risk of hearing loss, as are people who listen to loud music
on their headphones or who engage in noisy hobbies, such as hunting or motorcycling. Sounds
that are 85 decibels or more can cause damage to your hearing, particularly if you are exposed to
them repeatedly. Sounds of more than 130 decibels are dangerous even if you are exposed to