A cochlear implant (CI) is a surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf or severely hard of hearing. Cochlear implants are often referred to as a bionic ear.
Cochlear implants may help provide hearing in patients that are deaf due to damage to sensory hair cells
in their cochlea. In those patients, they can often enable sufficient
hearing to allow better understanding of speech. The quality of sound is
different from natural hearing, with less sound information being
received and processed by the brain. However, many patients are able to
hear and understand speech and environmental sounds. Newer devices and
processing strategies allow recipients to hear better in noise, enjoy
music, and even use their implant processors while swimming.
As of December 2010, approximately 219,000 people worldwide have
received cochlear implants; in the U.S., roughly 42,600 adults and
28,400 children are recipients.
The vast majority are in developed countries due to the high cost of
the device, surgery and post-implantation therapy. A small but growing
segment of recipients have bilateral implants (one implant in each cochlea).
- 1 History
- 2 Parts of the cochlear implant
- 3 Candidates
- 3.1 Type of hearing impairment
- 3.2 Age of recipient
- 3.3 Number of users
- 4 The operation, post-implantation therapy and ongoing effects
- 5 Cost
- 6 Efficacy
- 7 Risks and disadvantages
- 8 Functionality
- 8.1 Processing
- 8.2 Transmitter
- 8.3 Receiver
- 8.4 Electrode array
- 8.5 Speech processors
- 8.6 Programming the speech processor
- 9 Scientific and technical advances
- 10 Manufacturers
- 11 Controversy in the culture
- 12 See also
- 13 References
- 14 Further reading
- 15 External links
||This section needs additional citations for verification. (March 2012)
The discovery that electrical stimulation in the auditory system can create a perception of sound occurred around 1790, when Alessandro Volta (the developer of the electric battery)
placed metal rods in his own ears and connected them to a 50-volt
circuit, experiencing a jolt and hearing a noise "like a thick boiling
soup". Other experiments occurred sporadically, until electrical
(sound-amplifying) hearing aids began to be developed in earnest in the
The first direct stimulation of an acoustic nerve with an electrode was performed in the 1950s by the French-Algerian surgeons André Djourno and Charles Eyriès.
They placed wires on nerves exposed during an operation, and reported
that the patient heard sounds like "a roulette wheel" and "a cricket"
when a current was applied.
The first attempt to develop a clinical CI was in 1957 by Djourno and
Eyriès. A recipient was implanted with a single channel device.
Unprocessed sounds were transmitted via a pair of solenoid-like coils.
The link was therefore transcutaneous; it did not require a break in the
skin after implantation. This device failed after a short time and
another device was implanted. After this second device failed, Eyriès
refused to implant a third device. He urged Djourno to collaborate with
an industry partner to build a more reliable device. Djourno refused
because he believed that academia should not be tainted by commerce.
Djourno found another surgeon, Roger Maspétiol, who implanted a second
patient in 1958. Although these recipients were unable to understand
speech with the device alone, it helped with lipreading by providing the rhythm of the speech.
In 1961 Dr William House (an otologist), John Doyle (a neurosurgeon)
and James Doyle (an electrical engineer) commenced work on a
single-channel device in Los Angeles.
In one case a five-wire electrode was used but the same signal was
applied to all contacts. House’s work continued in the 1970s in
collaboration with engineer Jack Urban. Their implant was also a
single-channel device but, in this case, the speech was modulated onto a
carrier of 16 kHz. The device, manufactured by 3M,
was ultimately implanted in some thousand or so recipients and paved
the way for future clinical development of multichannel CIs. The House/3M unit was the first approved by the FDA for implantation in adults in 1984.
In 1964, Blair Simmons at Stanford University
implanted some recipients with a six-channel device. This device used a
percutaneous plug to enable the electrodes to be individually
stimulated. Recipients could still not understand speech through the
device but, importantly, it demonstrated that by stimulating in
different areas of the cochlea, different pitch percepts could be
In 1970, Robin Michelson, M.D., reported preliminary results of
cochlear implantation in three deaf adults implanted with gold wire
electrodes. Initially he teamed with Mel Bartz, an electrical engineer
working with Storz, Inc. Michelson's report to the American Academy of
Otolaryngology and Ophthalmology created a tempest. Orthodox auditory
theory was in confusion at the time, and it was not thought possible for
direct electrical stimulation of neural tissue to convey meaningful
sound to the brain. Michelson conducted some work in San Francisco, in the Coleman Laboratory at the University of California,
a foundation funded by the wealthy ENT department chairman at UCSF,
Francis Sooy, MD. Michelson's implantation of humans before animal
physiology experiments caused consternation among physiologists,
audiologists, and many otologists. An otolaryngology resident, C. Robert
Pettit, heard Michelson describe the results of his cochlear
implantations at a department educational meeting. He ran to the Coleman
Laboratory, where Michelson spent one half-day per week away from his
Redwood City private ENT practice, and told the older surgeon of his
dream since college of a multi-channel electrode resembling a hairbrush.
Michelson said so many stimulus points were not necessary and that his
patients were hearing "in stereo" with a two-channel electrode he had
designed. Michelson and Pettit teamed to build the bipolar electrodes
embedded in silastic which replaced the broken gold electrodes in
Michelson's three patients. The reimplantation procedures were carried
out in Redwood City Community Hospital, not at UC San Francisco, as were
the original implants.
Soon, the UCSF department chairman recruited Michael Merzenich, a
young PhD, to carry out his research interests in neurophysiology,
mapping the inferior colliculus, and to investigate the potential of
cochlear implantation. Merzenich was enormously skeptical of the
cochlear implant project, but agreed to test cats Michelson and Pettit
had implanted. Merzenich was skilled at constructing micro-electrode
needles capable of penetrating single nerve cells without rupturing the
cell membranes and spilling cell contents. He agreed to monitor
electrical activity in inferior colliculus cells of cats
stimulated by normal sound in one ear, and electrical input from a
cochlear implant in the other ear, finding both auditory stimuli
similar. Merzenich had constructed an advanced electronic bank of signal
generating and monitoring equipment for use for in his mapping
experiments and a carefully shielded soundproof booth for testing. Over
the months of animal testing, Merzenich became convinced that the
electrical signal from the cochlear implant was entering the brain and
was "phase-locked." Understanding what humans heard with the cochlear
implant was another matter.
New tests were devised for implanted patients. One was congenitally
deaf and had never heard sound. Pettit employed a music professor to
synthesize simple tunes and sounds in various sound envelopes, and new pitch
and loudness-scaling tests were devised. When one of the reimplanted
patients was tested by the team under carefully controlled laboratory
conditions, in 1972, a version of "Where Have All the Flowers Gone?" played on a Moog Synthesizer
was presented to the patient through the cochlear implant. The camera
caught the patient humming the melody and tapping a pencil to the tempo
of the tune. That sequence convinced the department chairman to support
the cochlear implant project. When the film was shown to a meeting of
otologists later in 1972, it convinced the scientific community that
meaningful sound could be conveyed to the brain by electrical
stimulation of the auditory nerve.
Cochlear implants that operate successfully, including those produced
by all three major manufacturers (Cochlear Corporation, Advanced
Bionics and Med-El), incorporate the same basic design. Likewise, all
cochlear implants incorporate the same basic design to be capable of the
ultimate goal of "detecting" or "demodulating" intelligence from the
human voice when that intelligence is residing within an electronic
signal. The successful cochlear implant must also be capable of
converting the pattern of the detected intelligence into an appropriate
electronic format for application to the acoustic (eighth cranial)
nerve, which in turn further transmits the encoded pattern to the
hearing center of the brain, where the information is interpreted as
meaningful intelligence. That is why implants from all (three) major
manufacturers work equally well in functionality, but are quite
different in final design enhancements. Design of this basic conversion
process was first described by Adam Kissiah, Jr., and was first exposed
to the public when it was revealed to James O. Harrell, Esquire, Patent
Counsel to NASA's John F. Kennedy Space Center, in July, 1974. Mr.
Harrell also advised exposure to another person capable of understanding
the concept. This was done on August 1, 1974. Subsequent Patent Office
search and patent application for letters patent was completed in May
1977. Patent 4063048 was issued to Adam M. Kissiah, Jr. on December 13,
1977; Reissue 31031, which further improved design, was issued in
Some cochlear implant designs and intra-cochlear implantations were
made by others (see Cochlear Technology by Adam M. Kissiah, Jr.) prior
to the mid-1970s, and were considered "successful" from a surgical and
medical point of view. An equal number of proclamations and claims of
being "firsts" in cochlear implantation were also made. Indeed, many
important advances in cochlear implantation were accomplished during the
1960s and '70s. These earlier implants were capable of providing
background sounds, and provided some aid to lip reading, and thus
enabled patients to attain a most welcome sense of "attachment" to the
world of sound. These earlier implants were incapable, however, of
providing the ultimate level of comprehension of the intelligence of the
spoken human voice enjoyed by the implant users of today. This fact can
be supported by review of the many volumes of quarterly reports
provided by many researchers under contract to the National Institutes
Greater understanding of voice intelligence was accomplished as the
designs described in this first patent for the Cochlear Implant
(4063048, December 13, 1977) were utilized in subsequent cochlear
implants. Although Adam Kissiah was a full-time employee with NASA at
the Kennedy Space Center, he participated as a consultant in an
implantation program during the early 1980s through license agreement
granted by Kissiah to Biostim, Inc., who in turn participated (also by
contractual agreement) with Stanford University, Dr. Robert L. White and
Dr. F Blair Simmons, principal investigators, during their program of
cochlear implants (See Stanford University Cochlear Implant Program).
In 1976 a paper (received Feb 1975) was published by Pialoux, Chouard
and McLeod that stated that, in the six months before the paper's
submission, seven patients were implanted with an eight-channel device.
Although it was reported that about 50% of ordinary words were
understood without lipreading, this has not been supported by
audiological data in the literature.
In 1972 the House 3M single-electrode implant was the first to be commercially marketed. However, it was Dr. Michelson's patents and ultimately device which are thought of as the first cochlear implants.
Parallel to the developments in California, in the 1970s there were
two other groups working on the development of the cochlear implant in
Vienna, Austria, and Melbourne, Australia. On December 16, 1977,
professor Kurt Burian implanted a multichannel cochlear implant. The
device was developed by the scientists Ingeborg and Erwin Hochmair, who
founded MED-EL, producer of hearing implants, in 1989.
Professor Graeme Clark A.C., then Foundation Professor of the Department of Otolaryngology at the University of Melbourne
in 1970, led the team that developed the Australian prototype bionic
ear, which was implanted into the first patient, Rod Saunders, in 1978.
The prototype for the bionic ear developed by Professor
Clark can be seen at the National Museum of Australia in Canberra,
It is part of a collection acquired by the National Museum in 2009 and
includes key elements that figured in the development of the bionic ear,
including the prototype multi-channel cochlear implant received by Rod
Saunders in 1978 (subsequently removed when it was replaced by an
In December 1984, the Australian cochlear implant was
approved by the United States Food and Drug Administration to be
implanted in adults in the United States. In 1990 the FDA lowered the
approved age for implantation to two years, then 18 months in 1998, and
finally 12 months in 2000, although off-label use has occurred in babies as young as 6 months in the United States and 4 months internationally.
Throughout the 1990s, the large external components which had been
worn strapped to the body grew smaller and smaller, thanks to
developments in miniature electronics. By 2006, most school-age children
and adults used a small behind-the-ear (BTE) speech processor about the
size of a power hearing aid. Younger children have small ears and might
mishandle behind-the-ear speech processors, therefore, they often wear
the sound processor on their hip in a pack or small harness or wear the
BTEs pinned to their collar, barrette or elsewhere.
On October 5, 2005, the first of three recipients was implanted with Cochlear's TIKI device, a totally implantable cochlear implant, in Melbourne, Australia.
This was part of a research project conducted by Cochlear Ltd and the
University of Melbourne Department of Otolaryngology under the umbrella
of CRC HEAR to be the first cochlear implant system capable of
functioning for sustained periods with no external components. The
system is capable of providing hearing via the TIKI device in
stand-alone mode (invisible hearing) or via an external sound processor.
Although these recipients continue to use their devices successfully
today, it will be many years before a commercial product becomes
Since hearing in two ears allows people to localize sounds (given
synchronised AGCs) and to hear better in noisy environments, bilateral
(both ear) implants are being investigated and used. Users generally
report better hearing with two implants, and tests show that bilateral
implant users are better at localizing sounds and hearing in noise.
However, there is also evidence to suggest that the combination of one
implant with an FM system provides better speech recognition in noise
than two implants alone. Additionally, dynamic FM technology has been proven to outperform traditional FM when used with cochlear implants.
Nearly 3,000 people worldwide are bilateral cochlear implant users, including 1,600 children. As of 2006, the world's youngest recipient of a bilateral implant was just over 5 months old (163 days) in Germany (2004).
Parts of the cochlear implant
The implant is surgically placed under the skin behind the ear. The basic parts of the device include:
- one or more microphones which picks up sound from the environment
- a speech processor which selectively filters sound to prioritize audible speech, splits the sound into channels and sends the electrical sound signals through a thin cable to the transmitter,
- a transmitter, which is a coil held in position by a magnet placed behind the external ear, and transmits power and the processed sound signals across the skin to the internal device by electromagnetic induction,
The internal part of a cochlear implant (model Cochlear Freedom 24 RE)
- a receiver and stimulator secured in bone beneath the skin,
which converts the signals into electric impulses and sends them through
an internal cable to electrodes,
- an array of up to 22 electrodes wound through the cochlea,
which send the impulses to the nerves in the scala tympani and then
directly to the brain through the auditory nerve system. There are 4
manufacturers for cochlear implants, and each one produces a different
implant with a different number of electrodes. The number of channels is
not a primary factor upon which a manufacturer is chosen; the signal
processing algorithm is also another important block.
There are a number of factors that determine the degree of success to
expect from the operation and the device itself. Cochlear implant
centers determine implant candidacy on an individual basis and take into
account a person's hearing history, cause of hearing loss, amount of
residual hearing, speech recognition ability, health status, and family
commitment to aural habilitation/rehabilitation.
A prime candidate is described as:
- having severe to profound sensorineural hearing impairment in both ears.
- having a functioning auditory nerve
- having lived at least a short amount of time without hearing (approximately 70+ decibel hearing loss, on average)
- having good speech, language, and communication skills, or in the
case of infants and young children, having a family willing to work
toward speech and language skills with therapy
- not benefitting enough from other kinds of hearing aids, including
latest models of high power hearing instruments and FM systems
- having no medical reason to avoid surgery
- living in or desiring to live in the "hearing world"
- having realistic expectations about results
- having the support of family and friends
- having appropriate services set up for post-cochlear implant aural
rehabilitation (through a speech language pathologist, deaf educator, or
auditory verbal therapist).
Type of hearing impairment
People with mild or moderate sensorineural hearing loss
are generally not candidates for cochlear implantation. Their needs can
often be met with hearing aids alone or hearing aids with an FM system.
After the implant is put into place, sound no longer travels via the
ear canal and middle ear but will be picked up by a microphone and sent
through the device's speech processor to the implant's electrodes inside
the cochlea. Thus, most candidates have been diagnosed with a severe or
profound sensorineural hearing loss.
The presence of auditory nerve fibers is essential to the functioning
of the device: if these are damaged to such an extent that they cannot
receive electrical stimuli, the implant will not work. Some individuals
with severe auditory neuropathy may also benefit from cochlear implants.
Age of recipient
Post-lingually deaf adults, pre-lingually deaf
children and post-lingually impaired people (usually children) who have
lost hearing due to diseases such as CMV and meningitis,
form three distinct groups of potential users of cochlear implants with
different needs and outcomes. Those who have lost their hearing as
adults were the first group to find cochlear implants useful, in
regaining some comprehension of speech and other sounds. The outcomes of
individuals that have been deaf for a long period of time before
implantation are sometimes astonishing, although more variable.
The risk of surgery in the older patient must be weighed against the
improvement in quality of life. As the devices improve, particularly the
sound processor hardware and software, the benefit is often judged to
be worth the surgical risk, particularly for the newly deaf elderly
Infant with cochlear implant
Another group of customers are parents of children born deaf who want
to ensure that their children grow up with good spoken language skills.
The brain develops after birth and adapts its function to the sensory
input; absence of this has functional consequences for the brain, and
consequently congenitally deaf children who receive cochlear implants at
a young age (less than 2 years) have better success with them than
congenitally deaf children who first receive the implants at a later
age, though the critical period
for utilizing auditory information does not close completely until
adolescence. Additionally, a 2010 study into bilateral implantation
showed that children who receive their first cochlear implant before the
age of 1½ responded well to the second one, even if the second one was
implanted as late as 9 years old. In contrast, children who got their
implants at age 2½ years or later did not respond as well to the later
second implant, regardless of when they received it.
One doctor has said "There is a time window during which they can get
an implant and learn to speak. From the ages of two to four, that
ability diminishes a little bit. And by age nine, there is zero chance
that they will learn to speak properly. So it’s really important that
they get recognized and evaluated early."
The third group who will benefit substantially from cochlear
implantation are post-lingual subjects who have lost hearing: a common
cause is childhood meningitis. Young children (under five years) in
these cases often make excellent progress after implantation because
they have learned how to form sounds, and only need to learn how to
interpret the new information in their brains.
Number of users
By the end of 2008, the total number of cochlear implant recipients had grown to an estimated 150,000 worldwide.
A story in 2000 stated that one in ten deaf children in the United
States had a cochlear implant, and that the projection was the ratio
would rise to one in three in ten years.
Mexico had performed only 55 cochlear implant operations by the year 2000 (Berruecos 2000). Taiwan and China
announced an approximately $270 million order for cochlear implant
devices for children in 2006, which are being paid for by major
healthcare organization based in Taipei. These cochlear implants are a
donation by the Taiwanese organization
In India, there are an estimated 1 million profoundly deaf children,
only about 5,000 have cochlear implants. This minuscule number is due to
the high costs for the implant, as well as subsequent therapy.[