A cochlear implant prosthesis is a device that includes
an external package (microphone and speech processor) worn by the user
and an internal package (an array of electrodes that is surgically implanted
into the cochlea (end organ of hearing) in the inner ear. The internal
and external components of the cochlear implant are connected via an electric
coupling. Cochlear implant prostheses are designed to create hearing sensation
by direct electrical stimulation of auditory neurons (nerves). Several
designs of this prothesis have been used although they have similar basic
components. The speech processor is worn externally and converts characteristics
of sound signals (acoustic parameters) into electrical characteristics
(parameters). The purpose of the device is to improve speech recognition
of cochlear implant users by representing acoustic (sound) information.
The original single-channel implants have been replaced by greater use
of multichannel implants, where the stimulation is distributed across
an array of electrodes that evoke a wider range of auditory perception.
Cochlear implants are options for habilitation (i.e.,
helping a person develop or learn new skills or abilities) or rehabilitation
(i.e., helping a person relearn old skills that were lost somehow) available
for individuals with profound hearing impairment (Geers & Moog, 1994).
After long-term use with adults, a major research effort was undertaken
to evaluate effectiveness for children. In 1990 cochlear implants were
approved by the United States Food and Drug Administration for children
between the ages of 2 and 17. Considerable research has been directed
toward the effectiveness of these devices. Most early research focused
on the benefit gained from use of cochlear implants in conjunction with
speechreading (Geers & Moog, 1992). More recent research has investigated
the receptive and expressive language gains experienced by users of cochlear
implants (Hasenstab & Tobey, 1991). Early studies of children showed
that they followed a pattern similar to adults in that most users had
post-lingual hearing losses (i.e., after the age of five). More recently,
benefits to pre-lingually hearing impaired (i.e., before the age of two)
children have been observed. Research shows that pediatric implant users
gain substantial benefit from multichannel cochlear implants, that these
benefits develop over a long course of time, and that multichannel implants
are more beneficial than single-channel devices (Hasenstab, 1989).
Who Can Use this Technology?
Candidacy requirements for receiving a cochlear implant
are changing. Before the FDA approved implants, children with profound
deafness who were at least two years old, and who received no benefit
from conventional hearing aids, were the primary recipients. Several significant
factors interact in the consideration of cochlear implants as an option.
Age of onset of deafness is an important factor, specifically whether
the deafness was prelingual or postlingual. Etiology or cause of hearing
loss is significant as well. The majority of children with postlingual
deafness have meningitis as the cause of deafness. These children are
also at risk for additional outcomes such as neurological dysfunction
or cochlear ossification (hardening of the bone), presenting surgical
challenge. The majority of children receiving implants are prelingually
deaf and may be completely unfamiliar with sound.
Trends in effective use of cochlear implants have been
observed. The postimplant performance of children with acquired or congenital
deafness before age three show speech perception results that are similar.
The postimplant performance of children with postlingual deafness is better
on most outcome measures, but those differences become smaller over time.
Performance is better for children who are implanted when younger than
age four. The research has shown large within-group differences on all
measures that suggest that some factor(s) other than age of onset affect
postimplant performance differences. The traditional candidacy criteria
have been:
- Age 2 or older
- Profound deafness
- Consistent pattern of hearing aid use
- Intensive auditory training
- Hearing levels greater than 100 dB.
The traditional candidacy criteria have included only
those children who have demonstrated no benefit from conventional amplification.
Intensive auditory training should include training in detection of
sounds as well as recognition of closed sets of spoken works. In a closed
set, candidates are given options of words to choose from; in an open
set they must decide on a word without any clues. More recent changes
in candidacy criteria are leaning toward relaxing that criterion. The
performance of children with some residual hearing has resulted in a
recommendation to include them in the selection group. Comparative studies
of children with cochlear implants and with conventional hearing aids
have shown rapid gains (within six months) of the cochlear implant users
(Hasenstab & Tobey, 1991). Further research detailing changes with
respect to duration of implant use, significance of age of onset of
deafness, and age of implantation is needed.
What Are the Benefits of Cochlear Implants?
With adults the benefits of cochlear implants have ranged
from communication by hearing alone with ease (with or without speechreading)
to the recognition of sounds not available prior to the implant. Some
adults can recognize sounds in an open set with hearing alone. Adult
cochlear implant users are primarily individuals who have learned language
and then lost their hearing. The purpose of cochlear implants for children
is to enable them to develop spoken language. The benefits of implants
that have been shown in research include increased capacity for spoken
language acquisition. This has been observed as children move from no
recognition to substantial open set recognition within six months as
contrasted to much longer times required for hearing aid users to attain
this level of performance.
Some observers feel that successful implant use is related
to age of onset of deafness and implantation, etiology (cause of deafness),
type of prior language habilitation program (spoken or sign language),
parent involvement, and cognitive and language development. The enhanced
information about sound that is available to the user is one of the
major benefits of implants when contrasted to conventional hearing aids.
When implanted early after the onset of a loss, the enhanced perception
of sound may be expected to provide the child with the information required
for spoken language acquisition. Parents have reported rapid behavioral
improvement postimplant. Both parents and teachers have reported significant
receptive language improvement in phonologic (speech sounds) and semantic
(word meaning) domains. Increased intelligibility of speech has also
been reported. Cochlear implants are highly reliable but must be accompanied
by an intensive auditory rehabilitation component for successful use.
What Are the Limitations of Cochlear Implants?
Little is currently known about the long-term effect
of the cochlear implant. Implants require surgery. Although post-surgical
complications have been quite low, there are risks of infection with
surgical procedures. Although rare, the possibility of scalp flap complications
and migration (movement) of the electrode array from the scala tympani
(area in the inner ear) are present. The expense of the medical, audiological,
rehabilitation, and educational components of surgical implantation
is significant. Although uncommon, certain conditions may require re-implantation
of the device.
What Are Some Questions to Ask in Choosing Cochlear
Implants?
- Where can I find out more about cochlear implants?
- What type of communication development or rehabilitation
program has my child received to date?
- Do I have a philosophical commitment to spoken language
development for my child?
- When is the optimal time for my child to receive
an implant?
- Which ear will be implanted? Why?
- What are the surgical procedures and risks?
- How will I deal with after-hours emergencies or concerns?
- How will the rehabilitation plan be developed and
implemented?
- What is the long-term projection in terms of device
replacement and cost?
- Am I willing to commit the time, energy, and dedication
required to make the use of a cochlear implant a success?
- Is my child's school ready and able to work with
him as an implant user?
References and Additional Resources
American Speech and Hearing Association. (1986). Report
of the Ad Hoc Committee on Cochlear Implants. ASHA, 28-51.
Geers, A., & Moog, J. (1994). The effectiveness
of cochlear implants and tactile aids for deaf children. A report of
the CID sensory aids study. Volta Review, 96(5), 1-232.
Geers, A., & Moog, J. (1992). Speech perception
and production skills of students with impaired hearing from oral and
total communication education settings. Journal of Speech & Hearing
Research, 35 (1), 384-93.
Hasenstab, S. (1989). The multichannel cochlear implant
in children. Topics in Language Disorders, 9(4), 45-58.
Hasenstab, S., & Tobey, E. (1991). Language development
in children receiving Nucleus multichannel cochlear implants. Ear and
Hearing, 12(4), 55S-65S.
Miyamoto, R., Osberger, M., Robbins, A., Myers, W.,
Kessler, K.(1993). Prelingually deafened children's performance with
the Nucleus multichannel cochlear implant. American Journal of Otology,
15, 9-14.
National Institutes of Health (NIH). Cochlear Implants
in Adults and Children. 100th NIH Consensus Development Conference.
Bethesda, MD, May 1995.
Nevins, M. & Chute, P. (1995). Children with cochlear
implants in educational settings. Washington, DC: A.G. Bell Assn for
the Deaf.
Staller, S., Dowell, R., Beiter, A. (1991). Perceptual
abilities of children with the Nucleus 22 channel cochlear implant.
Ear & Hearing, 12(4), 34S-47S.
Tobey, E. (1993). Speech production. In R.S. Tyler (Ed.)
Cochlear implants: Audiological foundations. San Diego, CA: Singular
Publishing Group.
A.G. Bell Association for the Deaf, 3417 Volta Place,
NW, Washington, DC 10007.
American Speech-Language-Hearing Association (ASHA),
10801 Rockville Pike, Rockville, MD 20852.
Cochlear Implant Club International, 2000 Church Street,
Box 111 Nashville, TN 37236.
Division for Children's Communication Development, The
Council for Exceptional Children, 1920 Association Dr., Reston, VA 20191.
National Institute on Deafness and Other Communication
Disorders, 9000 Rockville Pike, Bethesda, MD 20892.
Network of Educators of Children with Cochlear Implants,
Manhattan Eye, Ear & Throat Hospital, 210 East 64th St., New York,
NY 10021.
Dr. Laughton is Associate Professor, Department of
Communication Science and Disorders, The University of Georgia.
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