Encyclopedia
A
cochlear implant is a surgically implanted electronic device that can help provide a sense of sound to a person who is profoundly deaf or severely hard of hearing. The cochlear implant is often referred to as a
bionic ear. Unlike other kinds of
hearing aids, the cochlear implant doesn't amplify sound, but works by directly stimulating any functioning auditory nerves inside the
cochlea with electrical impulses. External components of the cochlear implant include a microphone, speech processor and transmitter.
An implant does not restore or create normal hearing. Instead, under the appropriate conditions, it can give a deaf person a useful auditory understanding of the environment and help them to understand speech although post-implantation therapy may be required. According to researchers at the University of Michigan , approximately 100,000 people worldwide have received cochlear implants; roughly half are children and half adults. The vast majority are in
developed countries due to the prohibitive cost of the device, surgery and post-implantation therapy — Mexico had performed only 55 cochlear implant operations by the year 2000 .
Cochlear implants have met some controversy as their introduction has seen the renewal of a century-old debate about models of deafness that often has the hearing parents of deaf children on one side and the
Deaf community on the other. On the other hand, the modern medical ethics/law dictate that it is up to the patient or the legal guardian of the patients to decide whether one have the implant or not. Therefore, political debate about whether deafness is disability or not is irrelevant to current medical profession. On the other hand, whether society treats deafness as disability has direct bearing on the government policy. Many governments in the world have special legistration to help people with disabilities which, at least legally, include people who are deaf. Some
developed countries provide cochlear implantation for free. The debate is also economic. Many state-funded medical interventions for a disability are justified on the ground that, in the long run, they will prove cheaper for the state.
While cochlear implants have been welcomed by late-deafened adults and hearing parents of deaf children who are assisted by audiologists, speech pathologists, and surgeons, the implantation of deaf children has been vigorously opposed by many from the signing Deaf community.
History
The discovery that electrical stimulation to the auditory system can create a perception of sound occurred around 1790, when
Alessandro Volta 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 hearing aids began to be developed in earnest the 20th century.
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.
In 1961, American doctor William House had Djourno's paper translated and had devices made which he implanted into three patients. In 1969, with the help of Jack Urban, House created the first wearable cochlear implant. House's technology used a single electrode and was designed to aid lip-reading. Throughout the 1970s,
Melbourne researcher Graeme Clark developed implants which stimulated the
cochlea at multiple points, and on 1 August, 1978, Melbourne resident Rod Saunders become the first person in the world to receive a multi-channel cochlear implant.
In December 1984, the Australian cochlear implant was approved by the United States
Food and Drug Administration to be implanted into adults in the
United States. In 1990 the FDA lowered the approved age for implantation to 2 years, then 18 months in 1998, and finally 12 months in 2002, although special approval has been given for 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. Today , most school-age children and adults use a small behind-the-ear speech processor about the size of a power hearing aid. Younger children have small ears and might mishandle a BTE. Therefore, they often wear the speech processor on their hip in a pack or small harness. The processor is connected by a wire to the microphone and transmitter at ear or head level.
Since hearing in two ears allows people to localize sounds and to hear better in noisy environments, bilateral implants are currently being investigated. Users generally report better hearing with two implants, and tests show that bilateral implant users are better at localizing sounds and hearing in noise. Nearly 3000 people worldwide are bilateral cochlear implant users, including 1600 children.
As of 2006, the world's youngest recipient of a bilateral implant was just over 5 months old in Germany .
Parts of the cochlear implant
The implant is surgically placed under the skin behind the ear. The basic parts of the device include:
- External:
- a microphone,
- a speech processor which selectively filters sound to prioritise audible speech and sends the electrical sound signals through a thin cable to the transmitter,
- a transmitter, which is a magnetic pad placed behind the external ear, and transmits the processed sound signals to the internal device by electromagnetic induction,
- Internal:
- 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 24 electrodes wound through the cochlea, which send the impulses directly into the brain.
Who can use a cochlear implant?
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 a short amount of time without hearing
- 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 being benefited byother kinds of hearing aids
- 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.
Type of hearing impairment
Once a cochlear implant is put in place, any residual hearing a person has in that ear most likely will be destroyed. For this reason, people with mild or moderate sensorineural hearing loss or conductive hearing loss are generally not candidates for cochlear implantation. 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 candidates most frequently are diagnosed with profound sensorineural hearing loss.
The presence of auditory nerve fibres 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. A small number of individuals with severe auditory neuropathy may also benefit from cochlear implants.
Age of recipient
Post-lingually deaf adults and pre-lingually deaf children form two 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. If an individual has been deaf for a long period of time, the brain may begin using the area of the brain normally used for hearing for other functions. If such a person receives a cochlear implant, the sounds can be very disorienting, and the brain often will struggle to readapt to sound.
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 patient.
The other group of customers are parents of children born deaf who want to ensure that their children grow up with good spoken language skills. Research shows that congenitally deaf children who receive cochlear implants at a young age 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.
The operation, post-implantation therapy and ongoing effects
The device is surgically implanted under a general anaesthetic, and the operation usually takes from 1½ to 5 hours. The patient normally remains in hospital for one day for adults and 1-2 days for children, though many go home the same day. It is considered outpatient surgery. As with every medical procedure, the surgery involves a certain amount of risk; in this case, the risks include skin infection, onset of tinnitus, damage to the
vestibular system, and damage to facial nerves that can cause muscle weakness, or, in worst cases, disfiguring paralysis. The operation also usually destroys any residual hearing the patient may have; as a result, some doctors advise single-ear implantation, saving the other ear in case a biological treatment becomes available in future.
Results may not be immediate, and post-implantation therapy is required as well as time for the brain to adapt to hearing new sounds. In the case of congenitally deaf children, audiological training and speech therapy may continue for years. The participation of the child's family in working on spoken language development is considered to be even more important than therapy.
In 2003, the
CDC and FDA announced that children with cochlear implants are at a slightly increased risk of bacterial meningitis . Many users, audiologists, and surgeons also report that when there is an ear infection causing fluid in the middle ear, it can in fact affect the cochlear implant, leading to temporarily reduced hearing.
The implant has a few effects unrelated to hearing. Manufacturers have cautioned against
scuba diving due to the pressures involved, but the depths found in normal
recreational diving appear to be safe. The external components must be turned off and removed prior to swimming or showering. Some brands of cochlear implant are unsafe in areas with strong magnetic fields, and thus cannot be used with certain diagnostic tests such as
magnetic resonance imaging , but some are now FDA approved for use with certain strengths of MRI machine. Large amounts of static electricity can cause the device's memory to reset. For this reason, children with cochlear implants are also advised to avoid plastic playground slides. The electronic stimulation the implant creates appears to have a positive effect on the nerve tissue that surrounds it.
Cost
In the
United States, medical costs run from USD$45,000 to $70,000; this includes evaluation, the surgery itself, hardware , and rehabilitation. Some of this can be covered by health insurance. In
developed countries with a strong publicly-funded health care system, the rate of implantation is greater than in the US, as the costs are borne by the government. In
Australia,
Denmark and
Norway, 80 to 90% of deaf children have cochlear implants.
Efficacy
A cochlear implant will not cure deafness or hearing impairment, but is a prosthetic substitute for hearing. Some recipients find them very effective, others somewhat effective and some feel overall worse off with the implant than without. For people already functional in spoken language who lose their hearing, cochlear implants can be a great help in restoring functional comprehension of speech, especially if they have only lost their hearing for a short time.
British Member of Parliament Jack Ashley received a cochlear implant in 1994 at age 70 after 25 years of deafness, and reported that he has no trouble speaking to people he knows one on one, even on the telephone, although he might have difficulty with a new voice or with a busy conversation, and still had to rely to some extent on lipreading. He described the robotic sound of human voices perceived through the cochlear implant as "a croaking
dalek with laryngitis". Even modern cochlear implants have at most 24 electrodes to replace the 16,000 delicate hair cells that are used for normal hearing. However, the sound quality delivered by a cochlear implant is often good enough that many users do not have to rely on speech-reading .
Rush Limbaugh, U.S. talk radio show host, says that everything sounds normal except that he cannot pick out the melody of new music that he had not heard prior to becoming deaf.
Adults who have grown up deaf often find the implants ineffective or irritating because their brain is unable to interpret sound after such a long period of time. Some who were orally educated and used amplifying hearing aids have been more successful with cochlear implants, as use of the hearing aid functioned to maintain perception of sound.
For small children, there have been mixed results. Almost all children with implants hear quite well with a cochlear implant, but for a rare few, the auditory nerve is unable to be stimulated. Patients without a viable auditory nerve are usually identified during the candidacy process. Fewer than 1% of deaf individuals have a missing or damaged auditory nerve, which today can be treated with an Auditory Brainstem Implant. Recent research has suggested that children and adults can benefit from cochlear implants in order to aid in sound localization and speech understanding.
Risks and disadvantages
The
FDA reports that cochlear implant recipients may be at risk for
meningitis and that a minority of these cases, worldwide, have resulted in death. A study of 4,265 American children who received implants between 1997 and 2002 concluded that recipient children had a risk of pneumococcal meningitis more than 30 times greater than that for children in the general population. A later, UK-based, study found that while the incidence of meningitis in implanted adults was significantly higher than the general population, the incidence in children was no different than the general population.
Post operation, individuals living with cochlear implants that use rechargeable batteries may find travel difficult in countries with mismatched AC power sources or no power at all to charge their devices. Many devices use easily found non rechargeable batteries and will not have this problem.
Ethical issues
Cochlear implants for congenitally deaf children are often considered to be most effective when implanted at a young age, during the critical period in which the brain is still learning to interpret sound; hence they are implanted before the recipients can decide for themselves. Critics question the ethics of such invasive elective surgery on healthy children. They point out that manufacturers and specialists have exaggerated the efficacy and downplayed the risks of a procedure that they stand to gain from. On the other hand, Andrew Solomon from New York Times state that "Much National Association of the Deaf propaganda about the danger of implants is alarmist; some of it is positively inaccurate."
Much of the strongest objection to cochlear implants has come from the
Deaf community, which consists largely of pre-lingually deaf people who use a
sign language as their preferred language. Many in the Deaf comminity do not share the pathological view of deafness held by the hearing parent of deaf children that holds deafness as a disability to be "fixed". Instead, this group celebrates being Deaf and value their membership in the visual culture that they have grown up in . Many hearing people, on the other hand, feel that
refusing to implant deaf children is unethical, comparable to refusal to treat any other handicap or disease which has an effective treatment.
The conflict over these opposing models of deafness has raged since the 18th century, and cochlear implants are the latest in a history of medical interventions promising to turn a deaf child into a hearing child — or, more accurately, a child with a mild or moderate hearing impairment.
Critics argue that the cochlear implant and the subsequent therapy often become the focus of the child's identity, at the expense of a positive Deaf identity and the ease of communication in sign language. Measuring the child's success by their success in hearing and speech will lead to a poor self-image as "disabled" rather than having the healthy self-concept of a proud Deaf person.
Some writers have noted that children with cochlear implants are more likely to be educated orally and without access to
sign language . Children with implants are also often isolated from other deaf children and from sign language , and instead are 'married' to a team of hearing experts for the rest of their life who will monitor his cochlear implant and adjust the speech processor, at great expense. According to Johnston , cochlear implants have been one of the technological and social factors implicated in the decline of
sign languages in the developed world. Some of the more extreme responses from Deaf activists have labelled the widespread implantation of children as "cultural genocide". As cochlear implants began to be implanted into deaf children in the mid to late 1980s, the Deaf community responded with protests in the
US,
UK,
Germany,
Finland,
France and
Australia. Opposition continues today but in many cases has softened. As the trend for cochlear implants in children grows, deaf community advocates have tried to counter the "either or" formulation of oralism vs manualism with a "both and" approach; some schools now are successfully integrating cochlear implants with sign language in their educational programs. However, some opponents of sign language education argue that the most successfully implanted children are those who are encouraged to listen and speak rather than overemphasize their visual sense. This opposition to sign appears not to come so much from scientific evidence that signing impairs learning spoken language, but from a hysterical desire to have a "normal" child. Indeed, before cochlear implantation, many deaf children raised with the oral approach reported that they did not learn to speak until they already knew some form of sign language.
Dr. Robert Ruben, an ear nose and throat specialist at Montefiore Hospital in the Bronx, said: "If I had a deaf child, I would implant one ear, leaving the other free in case cures develop that require an intact inner ear. I would bring up that child bilingually. Parents could phase out sign later on if they wanted, but it should not be abandoned until it becomes clear that the child can develop satisfactory oral language. The worst mistake is for parents to neglect the one most important thing — that language of any kind, no matter what kind, must somehow be got into the child soon enough."
How the cochlear implant works
The implant works by using the tonotopic organization of the
basilar membrane of the inner
ear. "Tonotopic organization" is the way the
ear sorts out different
frequencies so that our
brain can process that information. In a normal ear,
sound vibrations in the air lead to resonant vibrations of the
basilar membrane inside the
cochlea. High-frequency sounds do not pass very far along the membrane, but low frequency sounds pass farther in. The movement of hair cells, located all along the basilar membrane, creates an electrical disturbance that can be picked up by the surrounding
nerve cells. The brain is able to interpret the nerve activity to determine which area of the basilar membrane is resonating, and therefore what sound frequency is being heard.
In individuals with sensorineural hearing loss, hair cells are often fewer in number and damaged. Hair cell loss or absence may be caused by a genetic mutation or an illness such as
meningitis. Hair cells may also be destroyed chemically by an ototoxic medication, or simply damaged over time by excessively loud noises. The cochlear implant by-passes the hair cells and stimulates the cochlear nerves directly using electrical impulses. This allows the brain to interpret the frequency of sound as it would if the hair cells of the basilar membrane were functioning properly .
Processing
Sound received by the
microphone must next be processed to determine how the electrodes should be activated. The simplest way of processing would be to divide the acoustic signal by the number of electrodes in the device and apply the resulting voltage to the appropriate electrode. More sophisticated processing
algorithms are used in practice because applying
voltage to each of the electrodes simultaneously could cause non-charge-balanced currents to flow between the electrodes. This could stimulate the nerves in undesirable ways and lead to both tissue and electrode damage.
Fourier strategies use
bandpass filters to divide the signal into different frequency bands. The algorithm chooses a number of the strongest outputs from the filters, the exact number depending on the number of implanted electrodes and other factors. These strategies emphasize transmission of the temporal aspects of speech.
Feature extraction strategies use features which are common to all
vowels.
Each vowel has a fundamental frequency and
formants . The pattern of the fundamental and formant frequencies is specific for different vowel sounds. These algorithms try to recognise the vowel and then emphasise its features. These strategies emphasize the transmission of spectral aspects of speech. Feature extraction strategies are no longer widely used.
Transmitter
This is used to transmit the processed sound information over a
radio frequency link to the internal portion of the device. Radio frequency is used so that no physical connection is needed, which reduces the chance of infection. The transmitter attaches to the receiver using a
magnet that holds through the skin.
Receiver
This component receives directions from the speech processor by way of radio waves sent from the
transmitter. The receiver is also a sophisticated mini
computer that translates the processed sound information and controls the electrical current sent to the electrodes in the
cochlea. It is embedded in the
skull behind the
ear.
Electrode array
The electrode array is made from a type of silicone rubber, while the electrodes are
platinum or a similarly highly conductive material. It is connected to the internal receiver on one end and inserted into the
cochlea deeper in the
skull. . When an electrical current is routed to an intracochlea electrode, an
electrical field is generated and auditory nerve fibers are stimulated.
Programming the speech processor
The cochlear implant must be programmed individually for each user. The programming is performed by an audiologist trained to work with cochlear implants. The audiologist sets the minimum and maximum current level outputs for each electrode in the array based on the user's reports of
loudness. The audiologist also selects the appropriate speech processing strategy and program parameters for the user.
Manufacturers
Currently , the top three cochlear implant devices are manufacted by , , and . These are similar devices. Each manufacturer has adapted some of the successful innovations of the other companies to their own devices. There is no clear-cut consensus that any one of these implants is superior to the others. Users of all three devices display a wide range of performance after implantation.
Since the devices have a similar range of outcomes, other criteria are often considered when choosing a cochlear implant: usability of external components, cosmetic factors,
battery life, reliability of the internal and external components, customer service from the manufacturer, the familiarity of the user's surgeon and audiologist with the particular device, and anatomical concerns.
Cochlear implant in popular culture
In 2000, an Academy Award nominated film
Sound and Fury depicted this cultural divide. The Artinian family themselves are a "microcosm" of the
deaf culture war and two children – Peter and Heather – are caught in the middle. Many of the family members who opposed cochlear implants later went on to receive implants or allow their children to be implanted, and have become strong advocates for cochlear implants.
Famous recipients of cochlear implants include British MP Jack Ashley, conservative U.S. talk-show host
Rush Limbaugh, British designer and typographer Tony Malone, and Heather Whitestone, Miss America 1995.
On the television show
ER, Reese Benton, the son of Dr. Peter Benton, is born deaf and his father briefly considers giving his son a cochlear implant.
See also
References
- Berruecos, Pedro. . Cochlear implants: An international perspective - Latin American countries and Spain. Audiology. Hamilton: Jul/Aug 2000. Vol. 39, 4:221-225
- Chorost, Michael. . Rebuilt: How Becoming Part Computer Made Me More Human. Boston: Houghton Mifflin.
- Djourno A, Eyriès C. . 'Prothèse auditive par excitation électrique à distance du nerf sensoriel à l'aide d'un bobinage inclus à demeure.' In: La Presse Médicale 65 no.63. 1957.
- Djourno A, Eyriès C, 'Vallencien B. De l'excitation électrique du nerf cochléaire chez l'homme, par induction à distance, à l'aide d'un micro-bobinage inclus à demeure.' CR de la société.de biologie. 423-4. March 9, 1957.
- Eisen MD , 'Djourno, Eyries, and the first implanted electrical neural stimulator to restore hearing.' in: Otology and Neurotology. 2003 May;24:500-6.
- Grodin, M. . Ethical Issues in Cochlear Implant Surgery: An Exploration into Disease, Disability, and the Best Interests of the Child. Kennedy Institute of Ethics Journal 7:231-251.
- Johnston, Trevor. . Wither the Deaf Community? In 'American Annals of the Deaf' ,
- Lane, H. and Bahan, B. . Effects of Cochlear Implantation in Young Children: A Review and a Reply from a DEAF-WORLD Perspective. Otolaryngology: Head and Neck Surgery 119:297-308.
- Lane, Harlan , Cochlear Implants:Their Cultural and Historical Meaning. In 'Deaf History Unveiled', ed. J.Van Cleve, 272-291. Washington, D.C. Gallaudet University Press.
- Lane, Harlan , The Cochlear Implant Controversy. World Federation of the Deaf News 2 :22-28.
- Litovsky, Ruth Y., et. al. . "Bilateral Cochlear Implants in Children: Localization Acuity Measured with Minimum Audible Angle." Ear & Hearing, 2006; 27; 43-59.
- Miyamoto,R.T.,K.I.Kirk,S.L.Todd,A.M.Robbins,and M.J.Osberger. . Speech Perception Skills of Children with Multichannel Cochlear Implants or Hearing Aids. Annals of Otology, Rhinology and Laryngology 105 :334-337
- Officiers, P.E., et. a. . "International Consensus on bilateral cochlear implants and bimodal stimulation." Acta Oto-Laryngologica, 2005; 125; 918-919.
- Osberger M.J. and Kessler, D. . Issues in Protocol Design for Cochlear Implant Trials in Children: The Clarion Pediatric Study. Annals of Otology, Rhinology and Laryngology 9 :337-339.
- Reefhuis J, et al. Risk of Bacterial Meningitis in Children with Cochlear Implants, USA 1997-2002. New England Journal of Medicine, 2003; 349:435-445.
- Spencer, Patricia Elizabeth and Marc Marschark. . Cochlear Implants: Issues and Implications. In 'Oxford Handbook of Deaf Studies, Language and Education', ed. Marc Marschark and Patricia Elizabeth Spencer, 434-450. Oxford: Oxford University Press, 2003.
External links
- Includes simulations of what someone with implants might hear.
- PBS article about advances in coclear implant technology with simulations of what someone with each type of implant would hear.
- : Author writes about his own implant and trying the latest software from researchers in a quest to hear music better.
- A memoir of getting a cochlear implant, published in 2005.
- A web site focusing on the signing deaf community.
- A family's account of their child's implant
- A 501 non-profit who provides free insurance appeal assistance to individuals who have been turned down by their insurers for cochlear implants
- A site that records the life of a person who has received a cochlear implant
- Information about hearing loss and cochlear implants.
