by Mandy Taylor
As the life expectancy of the general population continues toincrease, so has the number of people experiencing varying types ofperceptual loss. One area of perceptual loss that is gaining more andmore recognition is auditory functioning. The number of individualsexperiencing a post-lingual hearing loss, or hearing loss after theacquisition of language, is increasing among the older adults in oursociety. This increase has facilitated a need for a means of managingsuch a loss of functioning. The group of people affected by hearingloss is by no means strictly limited to older adults. Pre-linguallydeaf children and adults, as well as, postlingually deafenedindividuals can benefit from the technology that is currently beingdeveloped and refined for the management of hearing loss. Theconventional hearing aid is probably the most common device picturedwhen thinking in terms of managing hearing loss. However, anotheroption that may not be as well known is the cochlear implant.
The cochlear implant is a relatively new option in the managementof hearing loss. Cochlear implants amplify sound, code sound into anelectrical signal, and send those signals into the auditory nerve.The signal then travels to the auditory brainstem and onward to thetemporal lobe of the brain for interpretation. The cochlear implantsystem consists of internal and external components. The internalcomponents include a receiver, an internal magnet, and an electrodearray. During a surgical procedure, a space is made in the mastoidbone behind the ear. This space holds the internal magnet andreceiver. The electrode array is then placed in contact with thenerve endings in the cochlea. After implantation surgery, the skinand hair around the incision are allowed to heal for about fiveweeks.
Then the patient is fitted with the external components of theimplant. These components include a microphone, an externaltransmitter coil, cords, and a speech processor. The microphone isattached to the ear by means of an earhook. The microphone picks upsound waves and sends them to the transmitter for convertion into anelectrical signal. The transmitter coil is held in place against thepatient's head by means of an external magnet that is attracted tothe internal magnet. A cord connects the microphone to thetransmitter coil. Another cord then connects the microphone to thespeech processor. The speech processor contains a software programthat determines how sound waves will be coded and transformed intoelectrical impulses. When the incoming sound has been coded by theprocessor, an electrical signal travels back to the transmitter. Thetransmitter then sends high-frequency radio waves to the internalreceiver. In the internal receiver, the radiowaves are converted backto electrical impulses that travel, by way of auditory nerves, to thearea of the brain where sound is interpreted (Tye-Murray, 1992).
Individuals with cochlear implants have been the subjects ofnumerous tests and experiments focusing on the functioning of theauditory system. These studies include experiments dealing with howthe pitch of sounds and voices is processed and with the recognitionof words at normal speaking rates. Because the technique bypasses thecochlea and stimulates the auditory nerve directly, implant users canbe studied for the loudness coding mechanisms of the human auditorysystem.
The electric stimulation and resulting loudness perceived by thesubjects in one study was shown to depend on stimulus frequency andintensity. Zeng and Shannon (1994) propose a two stage model whichsuggests that high-frequency stimuli are processed by the mechanicalmechanisms of the cochlea, and low-frequency stimuli are processed byneural mechanisms.
Other studies have focused on the abilities of adults withimplants to discriminate pitch rank and scale as well as recognizingspeech at soft and loud levels. Collins, Zwolan, & Wakefield (1997) focused on the ability of cochlear implant users todiscriminate pitch in relation to the area of stimulation of eachelectrode in the array. The orderly progression of frequency bandsalong the electrodes was found to aid in pitch perception. In anotherstudy examining speech recognition (Skinner, Holden, Holden,Demorest, & Fourakis, 1997), ten post-lingually deaf adults werepresented with vowels, consonants, words, and sentences under twocircumstances; simulated, soft conversation and raised-to-loud vocalefforts. These subjects were found to communicate successfully in avariety of listening situations ranging from 50 to 70 dB. Situationsof the conversational speaking level of 60 dB was shown tosuccessfully simulate the speech perception of everyday life.
The recognition of simple, familiar open-set words in shortstatements has also been evaluated. The understanding of everydaywords, improvement in lip-reading, and recognizing words andsentences are essential benefits to implant users. Factors found toinfluence word recognition include the sex of the speaker, rate ofspeaking, frequency of the vowel-consonant format of words, andduration of vowel sounds (Tyler, 1988). Other factors which influencethe communication and perception of speech for implant users areacoustic cues and features. The acoustic cues in speech recognitioninclude amplitude/time domain and the frequency domain. The receptionfeatures or articulation of words includes sounds with differingacoustical characteristics such as the stop consonants; b, d, g, p,t, k and the semi-vowels; w, r, l, y (Tyler, 1993).
Many of the studies conducted in relation to cochlear implantstend to focus on the effects of the implant on the existing auditorysystem, brain pathways, and structures. Although these areas ofresearch are crucial for the continued development of technologicallymore advanced devices, many times the thoughts and expectations ofthe patient can be overlooked. The expectations of the recipients andtheir families are every bit as important as the electricalconductivity of the implant. Unrealistic expectations can be verydamaging to the recipient. Realistic expectations of cochlear implantrecipients include an enhanced ability to speechread or recognizespeech using both auditory and visual signals. Some recipients candetect and recognize environmental sounds. Speech will soundmechanical in the beginning, and it takes time before speech willsound natural (Tyler, 1993). The cochlear implant, at this time, isby no means a Ňbionic earÓ. People with cochlear implants should notexpect a dramatic, overnight improvement in the auditory ability.Months of tuning sessions, practice recognizing and interpretingsounds, and aural rehabilitation may be necessary for even limitedsuccess with the cochlear implant.
Recipients and family members can also go through various stagesin reaction to a diagnosis of deafness. These stages begin with shockand disbelief, then recognition of the deafness, followed by denial,and finally ending with acknowledgment and constructive action. Theshock stage is often described as feeling of numbness in reaction tothe diagnosis. The recognition stage is a time of recognizing theseverity and repercussions associated with hearing loss. Denial isoften characterized by visits to many different doctors in search ofa differing opinion. The acknowledgment stage is very importantbecause it is at this time that reasonable action and interventioncan be considered. It is at this time that the cochlear implant maybe introduced as an option for the management of hearing loss. Thisis also the time in which the expectations of the recipient should beaddressed. The unrealistic expectations for implant users can behandled in various ways. Approaches to dealing with unrealisticexpectations range from education and guidance to professionalcounseling (Kampfe, Harrison, Ottinger, Ludington, McDonald-Bell,& Pillsbury, 1993).
Another area where more research needs to be done is in thepsychological assessment of prospective recipients. Prospectivepatients and recipients must examine a number of items duringassessment. Individual testing and evaluations are necessaryrequirements to assess the suitability of the recipient. A test ofreading is important in order to gain an idea of the patient'sability to read and comprehend words in written form. Measures ofintellectual ability are important to insure understanding of theresponsibilities involved in maintaining and caring for the implant.Personality questionnaires and self-concept measures are valuable indetermining the mental state and capabilities of the patient forhandling the problems, slow progress, and unrealized goals that arepart of the adjustments to implantation. Major justifications for thepsychological assessment of a prospective patient help in determiningthe patientŐs ability to cope with the involved procedure. Theevaluation of the results of surgery and the collection of data foruse in future studies are additional reasons for assessment.Recipients need follow-up assessment in order to ensure nopsychological damage has been done. The recipientŐs psychologicalstate should be monitored for improvement or decline. Individualbenefits or disadvantages can be addressed with a professional otherthan an audiologist during this time. Emphasis is placed on recall,information processing, and the ability to attend to detail duringthese sessions. The personality, self-concept, and level ofdepression of the subject before and after implantation are allfactors considered within the psychological assessment (Aplin, 1993).
With increasing technology, the face of the recipient of acochlear implant is constantly changing. Pre- and postlinguallydeafened children and adults have all been shown to benefit invarying ways from the implant. In the future, cochlear implants maybe paired with hearing aids for improved speech and environmentalsound perception. The technology behind the cochlear implant hasalready led to the development of an auditory brainstem implant thatbypasses the cochlea altogether and stimulates the auditory nervedirectly. Genetic studies utilizing tissue cloning and regenerationmay eventually make devices for the management of hearing problemobsolete. Until that time, however, the cochlear implant will remainin the forefront for the management of hearing loss.
References
Alpin, Y. (1993). Psychological evaluation of adults in a cochlearimplant program. American Annals of the Deaf, 138(5),415-419.
Collins, L.M., Zwolan, T.A., & Wakefield, G.H. (1997).Comparison of electrode discrimination, pitch ranking, and pitchscaling data in postlingually deafened adult cochlear implantsubjects. Journal of the Acoustical Society of America,101(1), 440-454.
Kampfe, C.M., Harrison, M., Ottinger, T., Ludington, J.,McDonald-Bell, C.,& Pillsbury, H.C. (1993). Parental expectationsas a factor in evaluating children for the multichannel cochlearimplant. American Annals of the Deaf, 138(3), 297-303.
Skinner, M.W., Holden, L.K., Holden, T.A., Demorest, M.E.,&Fourakis, M.S. (1997). Speech recognition at simulated soft,conversational, and raised-to-loud vocal efforts by adults withcochlear implants. Journal of the Acoustical Society ofAmerica, 101(6), 3768-3781.
Tye-Murray, N. (1992). Cochlear implants and children: Ahandbook for parents, teachers, and speech and hearingprofessionals. Washington: Alexander Graham Bell Association forthe Deaf.
Tyler, R.S. (1988). Open-set word recognition with the 3M/Viennasingle-channel cochlear implant. Archives of Otolaryngology,Head, and Neck Surgery, 114, 1123-1126.
Tyler, R.S. (1993). Cochlear implants: Audiologicalfoundations. San Diego: Singular Publishing Group, INC.
Zeng, F., & Shannon, R.V. (1994). Loudness-coding mechanismsinferred from electric stimulation of the human auditory system.Science, 264, 564-565.