Introduction
“Cochlear implants are electronic devices that contain a current source and an electrode array that is implanted into the cochlea” (American Speech-Language-Hearing Association, 2004) and where electrical current is used for stimulating the surviving auditory nerve fibers. With the development of the cochlear implant having undergone a long history, this paper aims to discuss this history, focusing particularly on the evolution of the cochlear implant over the last thirty years. In addition, this paper discusses the advantages and disadvantages of the implant, as well as the public’s response to its development and use.
Early Beginnings of the Cochlear Implant
The development of the cochlear implant started with the invention of electricity and the many attempts by researchers to provide hearing through the electrical stimulation of the auditory system (“History of cochlear implants,” n.d.). In particular, interest in the development of methods to stimulate hearing stated in the eighteenth century when Alessandro Volta discovered the electrolyte cell (“History of cochlear implants,” n.d.). Volta would also be the first one to use electricity to stimulate the auditory system (“History of cochlear implants,” n.d.). Although Volta succeeded to somehow stimulate hearing with his device, the sounds produced were not satisfactory. The same resulted from the attempts of other researchers who succeeded Volta.
It was only in the early 1930s when interest in the artificial reproduction of hearing was renewed and major breakthroughs would be made in the 1950s and the 1960s (“History of cochlear implants,” n.d.). During that time, there was much skepticism about whether cochlear implant could be used to treat deafness (MED-EL, 2013). Researchers were refused funding by the National Institutes of Health based on moral grounds (Denworth, 2013). These researchers were shouted down at professional conferences as the idea of creating a device to allow the deaf to hear and speak was considered a cruel incentive for parents and even potentially harmful for children. However, by 1972, the cochlear implant would be marketed for the first time (“History of cochlear implants,” n.d.).
Developments in Cochlear Implant Systems from the 1980s to the 21st Century
Since the commercialization of the device in 1972, more than 1,000 implants would be made from 1972 to the 1980s (“History of cochlear implants,” n.d.). Hundreds of children received implants and in 1980, the age criteria for the device’s use would be reduced from 18 to 2 years (“History of cochlear implants,” n.d.). In November 1984, the marketing of the 3M/House cochlear implant would be formally approved by the FDA (Food and Drug Administration) (“History of cochlear implants,” n.d.). However, it was never approved by the FDA for use in children (American Speech-Language-Hearing Association, 2004).
The 3M/House cochlear implant, a single channel device, was well tolerated and allowed many users to improve their speech reading capabilities (American Speech-Language-Hearing Association, 2004). It also enabled some users to enjoy limited open set word recognition. On the other hand, the Nucleus 22 was the first multi-channel cochlear implant system. Its initial versions were not capable of transmitting 22 separate channels of information at a rate that was fast enough for speech coding, but further developments enabled the transmission of the first formant frequency (American Speech-Language-Hearing Association, 2004). At about the same time, another multi-channel cochlear implant system was being developed in Utah. It allowed for continuous analog signals to be simultaneously applied to 4 of the 6 intracochlear electrodes. It did not use a feature extraction system like the nucleus did (American Speech-Language-Hearing Association, 2004) , but despite their different approaches, the performance of the two multi-channel devices was very similar (American Speech-Language-Hearing Association, 2004). With either device, users were able to perform considerably “above chance on tests that measured open set word recognition skills” (American Speech-Language-Hearing Association, 2004). Similarly, the clinical trials that were conducted in the 1990s showed that performance with multi-channel cochlear implants was better than with a single-channel implant for postlingually deafened adults (American Speech-Language-Hearing Association, 2004).
In the 1990s, further improvements would be made on cochlear implants where electrode and speech processors would be used for the production of coding strategies that would be associated with successively higher levels of performance (“History of cochlear implants,” n.d.). It would also be noted that the success of the Nucleus device would lead to the acceptance of the implants as assistive devices (“History of cochlear implants,” n.d.). This resulted in the increase in implant patients and the minimization of the risks. More people would accept the benefits of the implants and they would be strongly recommended. Also, the FDA would approve the use of multi-channel cochlear implants in perrilingually deafened children as young as twelve months of age (American Speech-Language-Hearing Association, 2004).
Since the 1990s, further research has been dedicated to the improvement of the implant system design, with the goal of “identifying the best intracochlear array and simulation mode, refining the processing strategies available, and miniaturizing the external and internal hardware“ (American Speech-Language-Hearing Association, 2004). As of 2004, there were three FDA-approved multi-channel cochlear implant systems that were available in the United States. These included Cochlear Corporation’s Nucleus Cochlear Implant System; Advanced Bionics Corporation’s Clarion; and Medical Electronics Corporation’s Med-El (American Speech-Language-Hearing Association, 2004). All three systems resulted in improved performance, with the best users achieving 80 percent or higher on their sound only word recognition scores (American Speech-Language-Hearing Association, 2004). However, there were still some users who obtained limited open set word recognition. For these users, the cochlear implants were more useful when combined with speech-reading cues.
A comparison of the three cochlear implant systems available in the United States shows that although the three devices differ in their mechanisms and in the methods they use, they still share certain similarities. One is that all three systems provide for multi-channel stimulation (American Speech-Language-Hearing Association, 2004). Another is that all three use transcutaneous communication between the implanted electronic components and the externally worn hardware (American Speech-Language-Hearing Association, 2004). They don’t use other electronic components or wires that pass through the skin barrier. The implanted device contains a receiving coil while the external device consists of a transmitting coil. Radio frequency transmission is used for providing power to the implanted electronics and for controlling the level and type of simulation provided by the implants. On the other hand, magnets are used for maintaining contact between the receiving and transmitting coils. It should also be noted that the cochlear implant is the first permanently implanted device that is not powered by battery but instead draws power from the externally worn hardware.
A third similarity among the devices is that all of them make use of telemetry, a technology that is used for monitoring the integrity of the intracochlear electrodes after their implantation. This capability is critical as the implanted electronics can possibly malfunction. However, these malfunctions may not always be easily detected, especially with adults or young children who have very limited auditory experience.
Still, all of the cochlear implant systems provide various options for speech processing, specifically in the conversion of analog speech signals into electrical signals (American Speech-Language-Hearing Association, 2004). In particular, the speech processing strategy refers to the rules that are used for controlling how the conversion is processed. This includes the manner by which loudness, timing, and pitch information are translated into electrical signals that are transmitted to the internal electrodes. It should be noted that the developments in speech processing algorithms and strategies have been responsible for much of the improvements that have been made on cochlear implant systems from the 1990s to the early parts of the twenty-first century (American Speech-Language-Hearing Association, 2004). With these improvements, the patient and the programming audiologist can choose their preferred speech processing algorithm or strategy.
The three devices are also similar in the general process they use for speech programming (American Speech-Language-Hearing Association, 2004). This process usually consists of the establishment of “a threshold and a maximum stimulation level for each of the individual intrachoclear electrodes” (American Speech-Language-Hearing Association, 2004). These levels need to be customized for every user and must be adjusted a number of times during the first year of use and less frequently afterwards. The externally worn speech processor can also be programmed to enable the user to choose from a set of programs or programming strategies, in turn enabling the user to choose a different programming strategy for certain real-world listening conditions.
Still, the cost of each device is quite similar among the three manufacturers (American Speech-Language-Hearing Association, 2004). They also offer their customers with service contracts and warranties. In addition, all three manufacturers have ongoing research and development initiatives in order to further improve the way that their devices work. Finally, it should be noted that the overall performance that results from the use of cochlear implant systems vary among users, even among those who use the same device. While some users achieve very high levels of performance in the sound-only mode, others receive very little benefit and achieve little more than speech-reading improvement or environmental awareness (American Speech-Language-Hearing Association, 2004).
For patients who are not candidates for standard electrode arrays, special electrode arrays may be used (American Speech-Language-Hearing Association, 2004). Such patients would include those who have ossified cochlea (i.e. obstructed cochlea) or other cochlear malformations, as well as those who no longer have an intact auditory nerve.
Moreover, cochlear implants have so far been implanted in only one ear due to the “belief that one ear should be preserved in order to benefit from future technologies and due to the cost/benefit issues with a second device “ (American Speech-Language-Hearing Association, 2004). However, in people with normal hearing, the sound that reaches one ear is different from the sound that reaches the other ear in that the intensity or loudness is different and the times when they reach the ear are also different (American Speech-Language-Hearing Association, 2004). These differences enable the listener to identify the direction from which the sound comes, in turn enabling him or her to separate background noise from the speech signal. This ability is important as it enables a person to communicate effectively in situations where other people are talking amidst competing noise (American Speech-Language-Hearing Association, 2004). With the success of unilateral implantation and the improved functioning of people who use binaural hearing aids, researchers have started to explore whether the use of bilateral cochlear implants can provide cochlear implant users with increased localization benefits and improved speech understanding. However, studies conducted among a limited number of cochlear implant recipients have shown mixed results (American Speech-Language-Hearing Association, 2004). More specifically, some recipients experience improved speech understanding, especially in the presence of noise. However, for other users, the main benefit was enhanced sound localization, with little or no improvement when compared to unilateral performance (American Speech-Language-Hearing Association, 2004). In this regard, the outcome of bilateral implantation remains inconclusive. This is also partially due to the limited scope of the projects and the limited number of cochlear implant participants (American Speech-Language-Hearing Association, 2004).
It should be noted that cochlear implants cannot be used with people who have a damaged auditory nerve, which resulted from the removal of an acoustic tumor (American Speech-Language-Hearing Association, 2004). For these patients, electrode arrays can be placed in the cochlear nucleus. These are termed auditory brain stem implants (American Speech-Language-Hearing Association, 2004). Although this procedure results in moderate levels of open-set sentence recognition, it helps patients achieve an enhanced environmental sound awareness, enhanced lip-reading abilities, and enhanced speech pattern reception (American Speech-Language-Hearing Association, 2004).
Advantages and Disadvantages of Cochlear Implants
As with other forms of medical treatment and procedures, cochlear implants also have their advantages and disadvantages, which influence their level of acceptability by the public. The main advantage or benefit is that it enhances the patient’s hearing. However, the level of performance can vary, from a near normal ability to understand speech to no hearing benefit at all (FDA, 2014). Adults typically start to experience enhanced hearing immediately and it may continue to improve up to the third month after the initial tuning session, after which the improvement becomes slower, although the improvements may continue for many years (FDA, 2014). Cochlear implants also enable users to distinguish different types of sounds, such as the sound of a light switch being turned on or off; the sound of rustling leaves; the whistling of a tea kettle; the barking of dogs; the ringing of the telephone; and others. Moreover, the implant helps users understand speech even without lip-reading, although even for those who still need to lip-read, the implant helps nonetheless. Similarly, many users are able to make telephone calls and understand familiar voices over the telephone. In addition, many users can watch television more easily and some can enjoy music.
On the other hand, aside from the risks that may occur during surgery, the other disadvantages of a cochlear implant include the user possibly hearing sounds differently, that is, the sound impressions from an implant may be different from normal hearing (FDA, 2014). The sound may also seem synthetic, technical, or mechanical at first. However, it becomes more natural as the user becomes more accustomed to the implant. The implant may also cause a loss in residual hearing, that is, it may destroy any remaining hearing in the implanted ear. Similarly, the use of the cochlear implant may have unknown and uncertain effects, especially since the implant directly stimulates the nerves with electrical currents. Although this stimulation seems safe, the electrical currents’ long-term effects on the nerves are not known. Moreover, with users experiencing different levels of performance, those who do not have a very positive experience after receiving the implant may be disappointed. Unfortunately, there is no test that a patient can take to deter mine how successful the implant will be and how much it will help the user in understanding language. The user may also need to constantly change the implant’s sensitivity in order to hear loud and soft sounds. It may also need to be removed either temporarily or permanently if an infection occurs after the implant surgery. As well, if the implant fails then the patient may need to undergo additional surgery for the problem to be fixed. However, this would expose the patient to the risks of surgery again. Moreover, it may not be possible for some users to upgrade their implants when new external components become available without having to change the implant, too. Users will also not be able to undergo certain medical procedures such as ionic radiation therapy, electroconclusive therapy, electrical surgery, neurostimulation, and MRI imaging. As well, the implant depends on batteries and for some devices, the batteries need to be changed everyday. In addition, slips and falls, car accidents, contact sports, and other impacts near the ear may damage the implant, which may mean conducting another implant surgery. However, it is not known whether a new implant would function as well as the old one. As well, the replacement of the damaged or lost parts may be expensive.
Cochlear implant users will need to use the device for the rest of their life. This poses problems if the manufacturer goes out of business, leaving the user with nowhere to get the replacement parts or to avail of customer service. The implant may also change the user’s lifestyle as it will interact with the electronic environment. The user will also have to be careful with static electricity, which may temporarily or permanently damage the implant. Similarly, the implant can become damaged if it gets wet and can cause irritation in areas where the external part rubs the skin. Finally, the implant can create strange sounds when it interacts with magnetic fields.
Public Perception of Cochlear Implants
A controversy that surrounds cochlear implants is the definition of deafness as a disability (Henshaw, 2012). While the medical community considers deafness to be a disability that needs to be treated, many deaf individuals consider it a cultural identity rather than a disability. Because they closely identify with the community of deaf individuals and supporters, they tend to perceive cochlear implants as an implication that there is something wrong with them that needs to be fixed (Henshaw, 2012).
However, there are still those who support the use of cochlear implants as these devices enable them to speak language fluently like hearing people and would no longer require them to depend on interpreters (Rachel, 2008). Also, unlike in the 1970s when proponents of the cochlear implants were heavily criticized, their contributions are now being acknowledged and recognized. As an example, three pioneering researchers Blake Wilson, Ingerborg Hochmair, and Graeme Clark were awarded in 2013 with the prestigious Lasker-DeBakey Award for Clinical Medical Research for their contributions in the development of the implant (Denworth, 2013). Today, the medical field recognizes that the implant has “for the first time substantially restored a human sense with medical intervention and directly transformed the lives of hundreds of thousands “ (Denworth, 2013).
References
American Speech-Language-Hearing Association. (2004). Cochlear implants (Technical Report).
Retrieved from http:// www.asha.org/policy.
Denworth, L. (2013, September 19). What cochlear implants did for my son. The Wallstreet
http://online.wsj.com/news/articles/SB10001424127887324492604579082911107374876
FDA. (2014, June 6). Benefits and risks of cochlear implants. Retrieved from
http://www.fda.gov/medicaldevices/productsandmedicalprocedures/implantsandprostheti
cs/cochlearimplants/ucm062843.htm.
Henshaw, A. (2012, June 14). The pros and cons of cochlear implants. Retrieved from
http://www.symptomfind.com/health/cochlear-implants/.
History of cochlear implants. (n.d.). Retrieved from
http://biomed.brown.edu/Courses/BI108/BI108_2001_Groups/Cochlear_Implants
/history.html.
MED-EL. (2013, October 16). The early history of cochlear implants and MED-EL. Retrieved
Rachel (2008, April 5). Open-minded Deaf person’s views. Retrieved from
http://cochlearimplantonline.com/site/open-minded-deaf-persons-views/.
