Cochlear implant

Cochlear implant

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. The cochlear implant is often referred to as a bionic ear.

As of April 2009, approximately 188,000 people worldwide had received cochlear implants; in the United States, about 30,000 adults and over 30,000 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).

There is disagreement whether providing cochlear implants to children is ethically justifiable, renewing a century-old debate about models of deafness that often pits hearing parents of deaf children against the Deaf community.

History

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 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.

The first attempt to develop a clinical CI was in 1957 by Djourno and Eyriès [1]. 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. This Djourno refused to do 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 [2]. The House/3M unit was the first approved by the FDA (Food and Drug Administration of the USA) for implantation in adults in 1984.

In 1964, Blair Simmons at Stanford University [3] 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 via the device but importantly, it did demonstrate that by stimulating in different areas of the cochlea, different pitch percepts could be produced.

In 1976 a paper (received Feb 1975) was published by Pialoux, Chouard and McLeod [4] which stated that in the 6 months prior to the paper being submitted seven patients were implanted with an 8 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.

Also at the time a group at the University of California, San Francisco was formed by Francis Sooy, who recruited Robin Michelson and Michael Merzenich. This group did much basic neurophysiological research in the field. The group first collaborated with the company Storz Medical Instruments. The work eventually led to the formation of Advanced Bionics, a major medical implant manufacturing company.

In 1972 the House 3M single-electrode implant was the first to be commercially marketed. See Robin Michelson's patents here: Patent Patent 2.3M Power Point Presentation on the Cochlear Implant.

Parallel to the developments in California, in the seventies there were two other groups, working on the development of the Cochlear Implant in Vienna, Austria and Melbourne, Australia. On December 16, 1977 Prof. 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. Burian K,Hochmair E,Hochmair-Desoyer IJ,. Lesser MR (1979)

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 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 3 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 standalone 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 available.

Since hearing in two ears allows people to localize sounds (given synchronised AGC's) and to hear better in noisy environments, bilateral (both ear) implants are currently being investigated and utilized. 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 (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:

External:

• a microphone which picks up sound from the environment
• a speech processor which selectively filters sound to prioritize audible speech 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 the processed sound signals to the internal device by electromagnetic induction,

Internal:

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. Advanced Bionics produces implants with 16 electrodes and use a technique called current steering in which two electrodes are stimulated simultaneously with different current levels to produce intermediate virtual channels. The number of channels is not a primary factor upon which a manufacturer is chosen; the signal processing algorithm is also another important block.

Candidates

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
• 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. 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 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, pre-lingually deaf children and post-lingually impaired people (usually children) who have lost hearing due to diseases such as 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. If an individual has been deaf for a long period of time, the brain may begin using the area of the brain typically 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.

Another 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 (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. 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

It was estimated in 2002 that around 10,000 children in the US and an additional 49,000 people worldwide had received Cochlear implants. By the end of 2008, the total number of cochlear implant recipients has 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). China will be having 15,000 cochlear implant surgeries on children, which are being paid for by a Taiwanese philanthropist. There is concern that the follow-up services in China are not adequate to meet the needs of cochlear implanted children.

The operation, post-implantation therapy and ongoing effects

Cochlear implant as worn by user

The device is surgically implanted under a general anaesthetic, and the operation usually takes from 1½ to 5 hours. First a small area of the scalp directly behind the ear is shaven and cleaned. Then a small incision is made in the skin just behind the ear and the surgeon drills into the mastoid bone and the inner ear where the electrode array is inserted into the cochlea. The patient normally goes home the same day as or the day after the surgery, although some cochlear implant recipients stay in the hospital for 1 to 2 days. 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, impaired facial sensation, or, in the worst cases, disfiguring facial paralysis. There is also the risk of device failure, usually where the incision does not heal properly. This occurs in 2% of cases and the device must be removed. The operation also destroys any residual hearing the patient may have in the implanted ear; as a result, some doctors advise single-ear implantation, saving the other ear in case a biological treatment becomes available in the future.

After 1–4 weeks of healing (the wait is usually longer for children than adults) during which the wound must be kept dry, the implant is turned on or "activated". Results are typically not 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 typically continue for years, though infants can become age appropriate - able to speak and understand at the same level as a hearing child of the same age in a matter of months; however it is far more common for the process to take years. The participation of the child's family in working on spoken language development is considered to be even more important than therapy, because the family can aid development by participating actively - and continually - in the child's therapy, making hearing and listening interesting, talking about objects and actions, and encouraging the child to make sounds and form words.

In 2003, the CDC and FDA announced that children with cochlear implants are at a slightly increased risk of bacterial meningitis (Reefhuis 2003). Though this risk is very small, it is still 30 times higher than children in the general population, without proper immunizations. The CDC and other national health organisations (such as the UK) now follow the practice of providing prophylactic vaccination against pneumococcal meningitis [1]CDC page

Many users, audiologists, and surgeons also report that when there is an ear infection causing fluid in the middle ear, it can 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 (MRI), 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 US$45,000 to US$105,000; this includes evaluation, the surgery itself, hardware (device), hospitalization and rehabilitation. Some or all of this may be covered by health insurance. In the United Kingdom, the NHS covers cochlear implants in full, as does Medicare in Australia and Israel. According to the US National Institute on Deafness and Other Communication Disorders, the estimated total cost is $60,000 per person implanted.

A John Hopkins study determined that for a three-year-old child who receives cochlear implants can save $30,000 to $50,000 in special-education costs for elementary and secondary schools as they are more likely to be mainstreamed in school and thus use fewer support services than similarly deaf children.

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 worse overall 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.

Individuals who have acquired deafblindness (loss of hearing and vision combined) may find cochlear implants a radical improvement in their daily life. It may provide them with more information for safety, communication, balance, orientation and mobility and promote interaction within their environment and with other people, reducing isolation. Having more auditory information that they may be familiar with may provide them with sensory information that will help them become more independent.

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; whether one on one or 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". Another recipient described the initial sounds as similar to radio static and voices as being cartoonish, though after a year with the implant she said everything sounded right. 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 lipreading.

Adults who have grown up deaf can find the implants ineffective or irritating. This relates to the specific pathology of deafness and the time frame. Adults who are born with normal hearing and who have had normal hearing for their early years and who have then progressively lost their hearing tend to have better outcomes than adults who were born deaf. This is due to the neural patterns laid down in the early years of life - which are crucially important to speech perception. Cochlear implants cannot overcome such a problem. Some who were orally educated and used amplifying hearing aids have been more successful with cochlear implants, as the perception of sound was maintained through use of the hearing aid.

Children without a working auditory nerve may be helped with a cochlear implant, although the results may not be optimal. 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 bilateral cochlear implants in order to aid in sound localization and speech understanding. (See Offeciers et al. 2005)

Risks and disadvantages

Some effects of implantation are irreversible; while the device promises to provide new sound information for a recipient, the implantation process inevitably results in damage to nerve cells within the cochlea, which often results in a permanent loss of most residual natural hearing. While recent improvements in implant technology, and implantation techniques, promise to minimize such damage, the risk and extent of damage still varies.

In addition, while the device can help the recipient better hear and understand sounds in their environment, it is not as good as the quality of sound processed by a natural cochlea. The main problem is with the age of recipient. While cochlear implant restore physical ability to hear, this does not mean brain can learn to process and distinguish speech if recipient passed the critical period of adolescence. As a result, those born deaf who receive implant as adult can only distinguish the difference between simple sounds, such as a ringing phone vs a doorbell, while others who receive implant early can clearly understand speech. The success rate depends on a variety of factors, most critically with the age of recipient but also to do with technology used and condition of the recipient's cochlea.

The United States Food and Drug Administration reports that cochlear implant recipients may be at higher risk for meningitis. 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. As a result, the Centers for Disease Control and Prevention and the Food and Drug Administration both recommend that would-be implant recipients be vaccinated against meningitis prior to surgery.

Necrosis has been observed in the skin flaps surrounding cochlear implants. Hyperbaric oxygen has been shown to be a useful adjunctive therapy in the management of cochlear implant flap necrosis.

There are strict protocols in choosing candidates to avoid risks and disadvantages. A battery of tests are performed to make the decision of candidacy easier. For example, some patients suffer from deafness medial to the cochlea - typically acoustic neuromas. Implantation into the cochlea has a low success rate with these people as the artificial signal does not have a healthy nerve to travel along.

With careful selection of candidates, the risks of implantation are minimized.

Controversy

Discussions within the Deaf community continue to fuel controversy and emotional personal debates about health, rights of the individual citizen, language, ethics, and the effects of the device on Deaf culture. For some in the Deaf community, CIs are an affront to their culture, which as they view it, is a minority threatened by the hearing majority. This has been a problem for the Deaf community and goes back as far as the 18th century with the argument of manualism vs. oralism. Another part of the controversy concerns the basic right of an individual to choose a language versus an individual as a young child having a mode of communication and language chosen for them. In the past, many adults whose first language is sign language endured policies created by medical and educational governing bodies that enforced the use of spoken language and use of hearing aids on them. In response, Deaf individuals have successfully advocated change to improve human rights for individuals, and they continue to work to advocate for change that will help children who are born with loss of hearing.

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 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 of the New York Times states 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 whose first language is a signed language. Regardless of the fact that to be deaf is to lack the ability to hear, many individuals who are deaf and the Deaf community do not share the view of deafness held by many hearing parents of deaf children, who regard deafness as a disability to be "fixed". On the other hand, many people feel that refusing to implant deaf children is unethical, comparable to refusal to treat any other handicap or disease that can be effectively alleviated. Many individuals who can hear or who have become deaf due to injury or illness are not comfortable with the thought of a child who lacks the sense most commonly associated with human language.

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, into 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 Deaf identity and ease of communication in sign language. Measuring the child's success only by their mastery of hearing and speech will lead to a poor self-image as "disabled" (because the implants do not produce normal hearing) 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 (Spencer et al. 2003). Also, children with implants are often isolated from other deaf children and from sign language (Spencer 2003). Instead they are 'married' to a team of hearing experts who will monitor their cochlear implant and adjust the speech processor, at great expense. Children do not always receive support in the educational system to fulfill their needs as they may require special education environments and Educational Assistants. According to Johnston (2004), 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 is softening. 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.

Parents and children alike discuss their opinions on cochlear implants. Many children discuss the fact that many of their parents never asked them or discussed the idea of a cochlear implant with them. While some discuss the fact that their parents asked them about it and discussed it with them and that made it better. Young adults seem to have the worst experiences mainly for cosmetic reasons, but for some the cochlear implants just do not work for them. If a child is placed into a mainstream setting it makes it difficult for them because they feel like they do not fit in with their peers and cannot fully identify with the Deaf community. One interviewee in the Christiansen and Leigh study states “In high school it was the worst time for me with the coch implant because I was really trying to find my identity with the cochlear implant…I never accepted my deafness. And the coch implant in some ways showed me that no matter what, the moment I take it off I’m deaf. I’ll never be hearing 24 hours.”

A 2007 study about attitudes of young, implanted people shows that although they are aware of the negative effects, their feelings about the implantation are overwhelmingly positive. None of the teenagers participating in the study criticised their parents for making the decision. They developed a positive identity and felt that they belonged to both the hearing and Deaf worlds although only some of them use both spoken and sign language.

Functionality

The implant works by using the tonotopic organization of the basilar membrane of the inner ear. "Tonotopic organization", also referred to as a "frequency-to-place" mapping, 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 (i.e. high pitched 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 bypasses 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 (see above).

Processing

Sound received by the microphone must next be processed to determine how the electrodes should be activated.

Filterbank strategies use Fast Fourier Transforms 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 spectral aspects of speech. Although coarse temporal information is presented, the fine timing aspects are as yet poorly perceived and this is the focus of much current research. Filterbank strategies use Fast Fourier Transforms 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 spectral aspects of speech. Although coarse temporal information is presented, the fine timing aspects are as yet poorly perceived and this is the focus of much current research. Filterbank strategies use Fast Fourier Transforms 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 spectral aspects of speech. Although coarse temporal information is presented, the fine timing aspects are as yet poorly perceived and this is the focus of much current research. Filterbank strategies use Fast Fourier Transforms 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 spectral aspects of speech. Although coarse temporal information is presented, the fine timing aspects are as yet poorly perceived and this is the focus of much current research. Filterbank strategies use Fast Fourier Transforms 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 spectral aspects of speech. Although coarse temporal information is presented, the fine timing aspects are as yet poorly perceived and this is the focus of much current research.

Feature extraction strategies used features which are common to all vowels. Each vowel has a fundamental frequency (the lowest frequency peak) and formants (peaks with higher frequencies). The pattern of the fundamental and formant frequencies is specific for different vowel sgfgsfgdfgsdfgsdngdhfgd hdfghfdgh dfghbdfgh dfgh df hdfhsdfgfdhdfhdgf fgdh dfghafdgfdhdfghdfghdf fdshg fsgh dfg dsg fgd sdf gdsfd dfsgfdsghsdfgdf a afdgsdf sdbsdf sdf bdsfg manufacturer tries to use a different strategy, Cochlear - 70% market share- for example uses the Speak-ACE strategy, ACE is mainly used; in which number of maxima (n) from the available maxima in sound are selected, Advanced bionics uses other techniques like CIS, SAS and HiRes, they stimulate the full spectrum. The processing strategy is a main block upon which one has to choose the implant manufacturer, research shows that patients can understand speech with as at least 4 electrodes, but the obstacle is in music perception, where it returns that fine structure stimulation is an important issue. Some strategies used in Advanced Bionics and Medel strategies make use of fine structure presentation by implementing the Hilbert Transform in the signal processing path, while ACE strategies depends mainly on the Short Time Fourier Transform.

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 and pain. 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 magnetic induction sent from the transmitter. (The receiver also receives its power through the transmission.) The receiver is also a sophisticated 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. (The cochlea winds its way around the auditory nerve, which is tonotopically organized just as the basilar membrane is). When an electrical current is routed to an intracochlear electrode, an electrical field is generated and auditory nerve fibers are stimulated.

In the devices manufactured by Cochlear Ltd, two electrodes sit outside the cochlea and acting as grounds-- one is a ball electrode that sits beneath the skin, while the other is a plate on the device. This equates to 24 electrodes in the Cochlear-brand 'nucleus' device, 22 array electrodes within the cochlea and 2 extra-cochlear electrodes.

Insertion depth is another important factor. The mean length of human being cochlea is 33–36 mm, due to some physical limitation, the implants don't reach to the apical tip when inserted but it may reach up to 25 mm which corresponds to a tonotopical frequency of 400–6000 Hz. Medel produced once a deep inserted implant that can get inserted up to a tonotopical frequency of 100 Hz (according to Greenwood frequency to position formula in normal hearing), but the distance between the electrodes is about 2.5 mm, while in the Nucleus Freedom from Cochlear Ltd is about 0.7 mm. There is a strong research in this direction and the best sounding implant can be subjective from patient to patient.

Speech processors

Speech processors are the component of the cochlear implant that transforms the sounds picked up by the microphone into electronic signals capable of being transmitted to the internal receiver. The coding strategies programmed by the user's audiologist are stored in the processor, where it codes the sound accordingly. The signal produced by the speech processor is sent through the coil to the internal receiver, where it is picked up by radio signal and sent along the electrode array in the cochlea.

There are primarily two forms of speech processors available. The most common kind is called the "behind-the-ear" processor, or BTE. It is a small processor that is kept worn on the ear, typically together with the microphone. This is the kind of processor used by most adults and older children.

The other form is called a body-worn-processor. This is the kind used typically by younger children, whose ears are too small to properly fit the bulky BTE processor. The body worn processor is kept on the user's body, and a long wire extends up to the microphone earpiece to connect it with the processor. Users of the body worn processor have to find some creative way where to place the body worn processor. Some mothers place the processor on the child's back in a pocket sewn onto a T-shirt or onesie, others use a harness that clips across the child's chest.

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.

Differences between Cochlear implants and hearing aids

Cochlear implants	Hearing aids
All characters are understandable	Only some characters
Unlimited possibilities for signal coding	Limited signal coding
Surgically implanted	No surgery needed
3 batteries or charged battery	1 battery
Battery life: 1 to 3 days	Battery life: 1 to 2 weeks
Success is individual and unpredictable	Success is individual and unpredictable
Rechargeable	Non- rechargeable

Scientific and technical advances

Professor Graeme Clark A.C. of La Trobe University, Melbourne, Australia announced beginning the development of a prototype "hi fi" cochlear implant featuring 50 electrodes. The increased number of electrodes is hoped to enable users to perceive music and discern specific voices in noisy rooms.

Researchers at Northwestern University have used infrared light to directly stimulate the neurons in the inner ear of deaf guinea pigs while recording electrical activity in the inferior colliculus, an area of the midbrain that acts as a bridge between the inner ear and the auditory cortex. The laser stimulation produced more precise signals in that brain region than the electrical stimulation commonly used in cochlear implants. Laser stimulation is a promising technology for improving the auditory resolution of implants but further research using fibre optics to stimulate the neurons of the inner ear is required before products using the technology can be developed.

Cochlear implants are rarely used in ears that have a functional level of residual hearing. However, Electric Acoustic Stimulation (EAS) devices, including the Hybrid "short-electrode" cochlear implant, have been developed that combine a cochlear implant with a sound amplifying hearing aid. EAS devices have the potential to make cochlear implants suitable for many people with partial hearing loss. The sound amplifying component helps users to perceive lower frequency sounds through their residual natural hearing while the cochlear implant allows them to hear middle and higher frequency sounds. The combination enhances speech perception in noisy environments.

Manufacturers

Currently (as of 2007), the three cochlear implant devices approved for use in the U.S. are manufactured by Cochlear Limited, Australia, MED-EL, Austria and Advanced Bionics, US. In the EU, an additional device manufactured by Neurelec, of France is available. 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 four 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, MRI compatibility, mapping strategies, customer service from the manufacturer, the familiarity of the user's surgeon and audiologist with the particular device, and anatomical concerns.

Cochlear Limited's 2007 annual report acknowledges that a Federal investigation continues into its payments to physicians and providers. In February 2007, part of the whistleblower complaint against Cochlear filed by former Chief Financial Officer Brenda March was unsealed by the U.S. District Court for the District of Colorado. The complaint alleges that Cochlear violated the Federal anti-kickback statute through its Partners Program, which offered credits towards free or discounted products for physicians who implanted Cochlear devices, as well as gifts, trips, and other gratuities paid to physicians and providers. The government intervened in the case and transferred it from the U.S. Department of Justice to the Health and Human Services Inspector General for the imposition of civil penalties. The amount of sanctions are not yet known.

See also

• Brain implant
• Electric Acoustic Stimulation
• Neuroprosthetics
• Noise health effects
• Hearing Aid

Resources

• Berruecos, Pedro. (2000). Cochlear implants: An international perspective - Latin American countries and Spain. Audiology. Hamilton: Jul/Aug 2000. Vol. 39, 4:221-225
• House, W. F., Cochlear Implants. Ann Otol Rhinol Larynogol 1976; 85 (suppl 27): 1 – 93.
• Simmons, F. B., Electrical Stimulation of the Auditory Nerve in Man, Arch Otolaryng, Vol 84, July 1966
• Pialoux, P., Chouard, C. H. and MacLeod, P. 1976. Physiological and clinical aspects of the rehabilitation of total deafness by implantation of multiple intracochlear electrodes. Acta Oto-Laryngologica 81: 436-441
• Chorost, Michael. (2005). Rebuilt: How Becoming Part Computer Made Me More Human. Boston: Houghton Mifflin.
• Christiansen, John B., and Irene W. Leigh (2002,2005). Cochlear Implants in Children: Ethics and Choices. Washington, DC: Gallaudet University Press.
• Cooper, Huw R. and Craddock, Louise C. (2006)Cochlear Implants A Practical Guide. London and Philadelphia: Whurr Publishers.
• Djourno A, Eyriès C. (1957). '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, (1957) '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 (2003), 'Djourno, Eyries, and the first implanted electrical neural stimulator to restore hearing.' in: Otology and Neurotology. 2003 May;24(3):500-6.
• Grodin, M. (1997). 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. (2004). W(h)ither the deaf Community? In 'American Annals of the deaf' (volume 148 no. 5),
• Lane, H. and Bahan, B. (1998). 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 (1993), 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 (1994), The Cochlear Implant Controversy. World Federation of the deaf News 2 (3):22-28.
• Litovsky, Ruth Y., et al. (2006). "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. (1995). Speech Perception Skills of Children with Multichannel Cochlear Implants or Hearing Aids. Annals of Otology, Rhinology and Laryngology 105 (Suppl.):334-337
• Officiers, P.E., et. a. (2005). "International Consensus on bilateral cochlear implants and bimodal stimulation." Acta Oto-Laryngologica, 2005; 125; 918-919.
• Osberger M.J. and Kessler, D. (1995). Issues in Protocol Design for Cochlear Implant Trials in Children: The Clarion Pediatric Study. Annals of Otology, Rhinology and Laryngology 9 (Suppl.):337-339.
• Reefhuis J, et al. (2003) 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. (2003). 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.
• 3M Power Point Presentation on the Cochlear Implant.

External links

• Cochlear Implant Online
• Cochlear Implants at Curlie
• Simulations for a CI
• Software for Cochlear Implant Simulation

General

• Cochlear Implants Information from the National Institutes of Health (NIH).
• NASA Spinoff article on engineer Adam Kissiah's contribution to cochlear implants beginning in the 1970s.

News reports

• http://www.esquire.com/dont-miss/wifl/regainhearing0807 Esquire Magazine article about a cochlear implant activation.
• NPR Story about improvements to improve the processing of music. Includes simulations of what someone with implants might hear.
• Tuning In PBS article about advances in cochlear implant technology with simulations of what someone with each type of implant would hear.
• My Bionic Quest for Boléro (Wired, November 2005): Author Michael Chorost writes about his own implant and trying the latest software from researchers in a quest to hear music better.
• Rationale for bilateral cochlear implantation (PDF)
• "For Some Who Lost Their Hearing, Implants Help", Jane E. Brody, New York Times, October 3, 2006.