The ear and hearing
Our ears are remarkable and dynamic organs that
enable us to hear both a pin drop and a thunderclap. They have three
sections: the outer ear, the
middle ear and the inner ear.
Sound waves in the air are collected outside the
head by the fleshy part of the outer ear (A). They are funneled
down the ear canal (B) to the ear drum (C).
These sounds then cause the ear drum to vibrate. The vibrations pass
along a chain of three tiny bones (D) within the air-filled
middle ear to a membrane in the wall of the cochlea (E). The
cochlea is the snail-shaped chamber of the inner ear. When the
vibrations enter the fluid inside the cochlea they move
ultra-sensitive hair cells that send electrical messages to the
auditory, or hearing nerve (F). This nerve then carries the
impulses up to the brain. It is only when the brain receives these
signals that we actually hear the sound.
A=pinna B=ear canal C=ear drum D=ossicles
E=cochlea F=auditory nerve
Each ear produces its own sounds
The snail-shaped cochlea (E) has two types
of hair cells. It is the inner ones that send the messages to the
brain. The job of the outer ones is to improve the sensitivity of our
hearing. As the outer hair cells do this important task they happen to
produce sound waves that travel back out of the ear. This means that
as we hear, tiny sound waves pass out of the cochlea (E),
through the middle ear (D) and into the ear canal (B).
Our ears therefore produce their own sounds!
These sounds are known as otoacoustic emissions
or OAEs. OAEs are very faint sounds, which is why we are not
usually aware of them. They are so quiet that if we want to study OAEs
we must use highly specialized equipment.
OAEs can be examined by playing a test sound into
an ear and then recording the unique sound that the hair cells of the
cochlea produce in return. The photo shows that this involves
fitting a small ear-piece snugly into a volunteer’s ear canal.
The ear-piece is connected to a computer. Clicking
sounds are played through a miniature loudspeaker housed in the
ear-piece. A very sensitive microphone, also in the ear-piece, then
picks up any OAE produced by the cochlea. The photo shows that
the computer then displays the OAE as a wavy line on the screen.
The wavy line that you see, shown more clearly
below, is an image of the sound wave, or OAE, that the cochlea has
produced in reply to the clicks that were played.
OAEs are individual to each person’s ear, rather
like a fingerprint is to the hand. This means that if we play the same
clicks into two ears, two different OAEs will emerge. The actual OAE
that an ear produces depends very much on the sound going inwards. So,
as we listen to different sounds such as speech and music, a variety
of unique sounds should also escape from our ears.
Research and OAEs
Medical research aims to discover how the body
works so that we can detect, prevent and treat its problems. Recording
OAEs under strict conditions allows the workings of the cochlea,
middle ear and ear drum to be examined as a whole. This has clinical
applications and at present OAEs form the basis of a screening test
for newborn babies. At the Institute of Hearing Research in
Southampton a new recording technique has been developed which is in
the process of being researched. It is hoped the technique will
improve existing OAE methods as well as open up a whole new area of
research with its own potential applications.
The Institute of Hearing Research, which is based
at the Royal South Hants Hospital, is jointly funded by the Medical
Research Council and the NHS Executive South East Region.
Both ‘pure’ and ‘applied’ research
are carried out. The pure research investigates what OAEs can tell us
about the workings of the ear. Applied research, on the other hand,
involves thoroughly checking the practical uses of OAEs in diagnosing
hearing problems. Overall, the work of the Institute offers an example
of the vital, yet behind-the-scenes, aspect of hospital life that is
|The Live Event
The Soundings live event has a double
1) a scientific demonstration of the how OAEs can
be recorded, and . . .
2) an artistic interpretation of the sounds
To illustrate how each person’s OAEs are
different, a scientist from the Institute of Hearing Research will
test volunteers and project the results onto a large screen. These
will then be traced by an artist so that the readings overlap. As the
tracings build up, an interwoven pattern emerges. This suggests some
of the hidden ways in which our senses respond to the world around us
and to other people. The screen will then become part of the