Cochlear implants
Cochlear implants are advanced electronic devices designed to assist individuals with severe hearing loss or deafness by directly stimulating the auditory nerve, allowing them to perceive sound. Unlike hearing aids, which amplify sound, cochlear implants convert sound waves into electrical impulses that the brain interprets as sound. The development of these implants is rooted in significant scientific discoveries, including those by mathematician Joseph Fourier, whose work on wave patterns aids in understanding sound, and Alessandro Volta, who demonstrated that electrical currents could stimulate hearing.
Cochlear implants function by utilizing signal processing techniques to analyze and transmit sound information, making use of strategies such as filter bank technology and feature extraction. While these devices can simulate aspects of normal hearing, they do not fully restore it, and recipients often need specialized training to interpret the signals as sound.
Candidacy for cochlear implants depends on various factors, including the individual's age, duration of deafness, and overall cochlear health. The procedure is not without controversy, as it can involve significant costs and the potential loss of any remaining natural hearing. Additionally, some members of the deaf community advocate for the preservation of deaf culture and express concerns over the implications of widespread cochlear implant use, fearing it may undermine their unique identity.
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Cochlear implants
SUMMARY: Cochlear implants use signal processing and algorithms to transmit electrical impulses to the brain to simulate hearing.
A cochlear implant is an electrical device that can help provide a representation of sound to a deaf or severely hard-of-hearing person. Unlike a hearing aid, a cochlear implant does not amplify sound; instead, it directly stimulates the auditory nerve, which sends these signals to the brain, where they can be interpreted as sound. Development of the cochlear implant relied in part on discoveries by French mathematician Joseph Fourier (1768–1830), whose studies in heat transfer led to the development of mathematics that can also be used to describe sound. Fourier analysis allows mathematicians to describe complex wave patterns, including the pressure waves that produce sound, as the combination of a number of component waves. Cochlear implants also draw on the discovery by the Italian physicist Alessandro Volta (1745–1827) that electrical current could be used to stimulate the auditory system and produce the sensation of sound. Practical work on cochlear implants dates back to the mid-twentieth century, and cochlear transplants were first approved by the U.S. Food and Drug Administration in 1984 for adults and in 1990 for children age 2 years and older (a limit since lowered to 12 months for one type of implant).
Sound Waves and Hearing
In a person with normal hearing, sound waves are collected by the outer (visible) ear (pinna) and sent down the ear canal to the eardrum (tympanic membrane). Movement of the eardrum is amplified by three small bones in the middle ear, commonly referred to as the “hammer,” the “anvil,” and the “stirrup,” before being passed on to the cochlea in the inner ear. In the cochlea, this information is converted into electrical impulses by the hair cells of the organ of corti, and these impulses are sent on to the brain, where they are interpreted as sound. The cochlea has a spiral shape (sometimes likened to that of a snail shell) and scientists have recently discovered that the shape itself is significant in the cochlea’s function. The spiral shape produces a “whispering gallery” effect as the energy of the frequency waves accumulate against the outer edge of the chamber, increasing humans’ ability to detect low-frequency sounds.
Signal Processing
Most sound, including speech, is complex, meaning that it consists of multiple sound waves with different frequencies. In a person with normal hearing, the ear acts as a kind of Fourier analyzer, which decomposes sound into components. A cochlear implant attempts to mimic this activity, translating sound waves into electrical impulses and transmitting them directly to the brain. Two basic signal-processing strategies have been used in designing cochlear implants: filter bank strategies, which use Fast Fourier Transforms to divide sound into different frequency bands and represent this information as an analog or pulsatile waveform; and feature-extraction strategies, which use algorithms to recognize and emphasize the spectral features of different speech sounds.
A cochlear implant somewhat simulates normal hearing rather than restoring it, and individuals who receive an implant require special training in order to learn to recognize the signals as sound. In addition, cochlear implants are not advisable for every type of hearing loss, and a number of factors should be considered by the individual and their physician before committing to an implant. These factors include current age, age at which the person became deaf, how long the person has been deaf, the availability of support (including financing) to see him or her through the training period, and the health and structure of the individual’s cochlea.
Although cochlear implants are growing in popularity and being used for younger and younger children, they are also controversial for several reasons, some of which were discussed in the 2000 documentary film Sound and Fury. One is based on the cost of the operation and follow-up therapy necessary to help the recipient learn to process the electrical impulses as sound. Another is that the surgery requires destroying whatever hearing may remain in the ear where the implant will be placed; for this reason, it is common to have the implant in one ear only. In addition, the surgery is done on children as young as one year in order to take advantage of peak language learning periods, so parents must make this decision for their children. Finally, many members of the deaf community feel that they should not be regarded as being defective or handicapped, that they can function successfully in the world using sign language and lip reading. They fear that widespread adoption of cochlear implants will ultimately destroy a distinctive and flourishing deaf culture.
Bibliography
Aronson, Josh. Sound and Fury. Aronson Film Associates, Inc. and Public Policy Productions, 2000. Filmstrip.
"Cochlear Implants." Mayo Clinic, 26 April 2024, www.mayoclinic.org/tests-procedures/cochlear-implants/about/pac-20385021. Accessed 17 Dec. 2024.
Loizou, Philipos. “Mimicking the Human Ear: An Overview of Signal-Processing Strategies for Converting Sound Into Electrical Signals in Cochlear Implants.” IEEE Signal Processing Magazine (September 1998).
Manoussaki, Daphne, E. Dimitriadis, and R. S. Chadwick. “The Cochlea’s Graded Curvature Effect on Low Frequency Waves.” Physical Review Letters 96 (March 3, 2006).
National Institute of Deafness and Other Communication Disorders, National Institutes of Health. “Cochlear Implants.” http://www.nidcd.nih.gov/health/hearing/coch.htm.
Niparko, John K., ed. Cochlear Implants: Principles and Practices. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2009.