FEATURE ARTICLE
The Design and Function of Cochlear Implants
Fusing medicine, neural science and engineering, these devices transform human speech into an electrical code that deafened ears can understand
Michael Dorman, Blake Wilson
Ludwig van Beethoven was 28 years old when he first noticed a ringing
and buzzing in his ears. Soon he was unable to hear high notes from
the orchestra; speech became indistinct. By 1802, four years after
the first symptoms, he was profoundly deaf.
Beethoven fell into a deep depression. He describes this period in
his Heiligenstadt Testament, meant to be read after his death:
For me there can be no relaxation in human society; no
refined conversations, no mutual confidences. I must live quite
alone and may creep into society only as often as sheer necessity
demands.... Such experiences almost made me despair, and I was on
the point of putting an end to my life—the only thing that
held me back was my art ... thus I have dragged on this miserable
existence.
In 2001, Scott N. was 34 and had lost all of his hearing. A surgeon
inserted 16 tiny electrodes into his inner ear, or cochlea,
and connected them to a small package of electronics implanted under
the skin. A year later, Scott came to author Dorman's laboratory at
Arizona State University to test his understanding of speech. The
results were extraordinary: Scott recognized 100 percent of more
than 1,400 words, either in sentences or alone, without any prior
knowledge of the test items.
As impressive as this performance was, the cochlear implant did not
restore normal hearing to Scott. The electrode array produced a
stimulus that was only a crude mimicry of the signals in a normal
cochlea. But as this example shows, a very high level of
functionality can be restored by a neural prosthesis that does not
recreate the normal system. For the thousands of people who have
received a cochlear implant, even an imperfect restoration of
hearing reconnects them to the world of sound. And it allows many of
them to use that most critical toy of modern life, the cell phone.
Although cochlear implants have a 40–year history culminating
in the current generation of high–performance devices, hearing
restoration is not universally welcomed. Among members of the Deaf
community, the absence of hearing is not necessarily viewed as a
disability. Some deaf parents refuse implants for their deaf
children, triggering an impassioned debate between those who agree
and those who challenge the decision. This article avoids that
controversy to focus on the science of cochlear implants. But recent
findings have influenced the temperature, if not the substance, of
the debate. As we point out, hearing must be restored at a very
early age if speech and language skills are to develop at a normal
rate. The decision to use or forgo the implant cannot wait until the
child—who must bear the consequences—reaches the age of consent.
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