Hearing Habilitation and Rehabilitation

Hearing habilitation or rehabilitation is the process of accessing the residual hearing of a Deaf/Hard of Hearing person through the use of assistive devices and/or auditory training techniques. The term "habilitation" (from the Latin habilitare, "to make able to") is generally used with children who were prelingually deafened - that is, before acquiring spoken language. "Rehabilitation" is used for children and adults who become Deaf/HoH after learning speech/language.

Hearing habilitation seeks to help the Deaf/HoH child access information from sound as much as possible. The purpose of accessing sound varies. Hearing parents often want their Deaf/HoH children to understand and produce speech sufficiently well to communicate in the hearing world. They choose spoken English as the child's intended primary language, since it matches their own. Other parents envision sound as an adjunct to sign language and/or speech reading; their chosen language may be sign or spoken English. Still others, particularly those whose children have profound hearing loss, are more concerned about the child's safety. They want the child to be able to hear warning sirens, trucks backing up, car horns, and fire alarms. Speech is not as important to these parents, so they usually choose sign language as the child's main form of communication.

For those who became Deaf/HoH after learning spoken language, the primary goal of rehabilitation is to recover the ability to communicate verbally. Individuals who experience hearing loss in adolescence or older usually do not have great difficulty with speech production, since they are familiar with the movements necessary and receive feedback from the muscles to determine accuracy. Younger children, whose speech patterns are not as defined, may have more trouble producing intelligible speech (depending on the degree of hearing loss). Also, they are still learning language, so they need extra attention in that area of development. For both groups, speech perception is essential.

However, some individuals, particularly in the case of profoundly Deafened young children, choose to change from spoken English to sign as the preferred language. In that case, as indicated above, rehabilitation may focus on hearing as an adjunct to sign or as a means of increased safety.

Choices about (re)habilitation will depend, in part, on the individual's or the parents' attitude about the meaning of Deafness. If being unable to hear is viewed as a liability that must be corrected at all costs (medical model), the most likely choice will be a cochlear implant or a powerful hearing aid along with therapy that emphasizes sound and may completely exclude sign. However, if it is viewed as part of an identity - a quality that allows a person to participate fully in Deaf culture (cultural model) - then hearing (re)habilitation may be minimal and will focus on sign language. Of course, those are the extremes, but attitudes may fall anywhere along the spectrum between the two.

The technology of the 21^st century has provided an array of assistive devices for hearing habilitation. The best known of these is the hearing aid, a device that amplifies sound to a level that will stimulate the auditory nerve. The amount of amplification required depends on the extent of hearing loss, which can be characterized as mild (20-40 dB), moderate (40-60 dB), severe (60-80 dB), or profound (80 dB HL or greater) ¹. The World Health Organization (WHO) defines these as follows: slight impairment (26-40 dB), moderate impairment (41-60 dB), severe impairment (61-80 dB) and profound impairment, including Deafness (81 dB or greater)².

A hearing aid contains a microphone, an amplifier, and a speaker. The most versatile type is the behind-the-ear (BTE) hearing aid, which can be used for mild to profound hearing loss. The BTE has a plastic case which contains the amplifier and, usually, the microphone. It is connected through a tube to an earmold that is specially made to fill the wearer's outer ear. Sound exits the earmold on the other side and passes down the ear canal.

Other types of hearing aids include in-the-ear (ITE) aids, which fit inside the outer ear, and in-the-canal (ITC) aids, which may be almost hidden in the ear canal. These types are not recommended for young children because the cases must be replaced frequently as they grow. With a BTE, only the earmold is replaced. In addition, ITE and ITC aids are not appropriate for severe to profound hearing loss since they lack the needed power and amplification³. Additionally, if the microphone and speaker are too close together there will be significant feedback at high gain, producing a high-pitched whine.

Body-worn hearing aids avoid the problem of feedback, since the microphone is located on the body and the speaker is in the ear. They are the most powerful type available and are suitable for children with the profound hearing loss. However, body aids do not allow for binaural localization of sound, an important factor in hearing habilitation.

The types of hearing aids listed above work best for individuals with sensorineural hearing loss. If the person has a conductive hearing loss - the inability to transmit sound through the outer and middle ears - the sound from a BTE or other hearing aid will have difficulty reaching the cochlea. This problem can be solved by a bone conduction hearing aid, a device which sends sound vibrations through the skull directly to the inner ear. It can be particularly useful for children with craniofacial abnormalities such as cleft palate who have developed conductive hearing loss after repeated ear infections. Bone conduction aids can be anchored to the mastoid process, the area of the skull behind the ear, via surgery⁴.

Since a hearing aid transmits sound to the inner ear, it requires some functioning hair cells in the cochlea in order to be effective. If the hair cells have been completely obliterated, or if there are not enough left to provide functional hearing, a cochlear implant may be chosen instead. A cochlear implant transforms sound into electrical impulses that are transmitted directly to the auditory nerve inside the cochlea. Its components include the microphone, speech processor, transmitting coil, antenna, electrode, and receiver/stimulator⁵.

Another option is the auditory brainstem implant. Since it bypasses the cochlea altogether, it can be used for individuals with damage to the auditory nerves. It operates like a cochlear implant except for the location of the electrodes, which are implanted in the auditory brainstem cochlear nucleus, the nerve center for hearing, at the base of the brain⁶.

Other devices used in hearing habilitation include FM systems (auditory trainers), which help the individual separate relevant speech from ambient noise, and personal amplifiers, often used during one-to-one conversation or television listening. Hearing aids and cochlear implants also offer telecoil settings, which are used to receive clear signals from the telephone or from an assistive device. In some public areas with many Deaf/HoH listeners, an induction loop is installed in the room itself, which will send signals to the telecoil in a hearing aid or cochlear implant. Separate telecoil receivers are available for those who do not need additional amplification⁷.

Auditory training encompasses many points of view about Deafness, from the auditory-verbal method which promises to allow children to "achieve their rightful places in our society,"⁸ to total or simultaneous communication, in which messages are presented through a variety of tools, both auditory and visual, in order to develop a common language⁹. In educational settings for Deaf children today, simultaneous communication is the most common since it allows for the child to learn the facts and concepts covered in school without concern about modality¹⁰.

The auditory-verbal method is a family-centered philosophy of hearing and listening for children who are Deaf or Hard of Hearing. An individualized program is developed by a therapist to meet the child's specific needs at a given stage of development. The focus is on audition (sound) alone, without any visual cues such as lip reading or gesture. Communication is through speaking and listening, so the child is taught a listening attitude as he or she is guided through a graduated series (easy to difficult) of auditory activities¹¹.

The goal of the auditory-oral approach is for the child to learn to understand and produce spoken language sufficient for communication with hearing persons. Speech reading (lip reading) is an important component. Teachers and therapists use gesture to draw the child's attention to the mouth and lips when they are speaking. They may also use gestures to point out objects of reference, indicate directions, and signify prepositions. Sign language is not used¹².

The goal of total communication is in its name - communication. In order to provide the easiest, least restrictive method to allow the child to communicate with his/her family, friends, and teachers, all modalities are used, particularly hearing (speech, vocalization, intonation) and vision (sign language, gestures, finger spelling, body language). Teachers and therapists using this method speak and sign simultaneously, conveying the same message through sight and sound, although the signs may not match speech word for word. Children are encouraged to use both sign and vocalization. In many cases, a child in a total communication program also receives speech therapy. Assistive devices are used to the greatest extent possible¹³.

According to the National Cued Speech Association, cued speech does not require hearing or speech, although it is often used by teachers and speech therapists to make speech clearer through vision. The speaker uses eight hand signals (cues) to represent different sounds of speech, and these hand signals remove the difficulty associated with speech sounds that are visually similar on the lips. For some individuals, the goal of cued speech is to aid in spoken language development so that the child can function in the hearing community. However, it was originally developed by Dr. Orin Cornett to improve literacy of Deaf students¹⁴.

References:

1. American Speech-Language-Hearing Association (ASHA) (2008).

Hearing assessment. Retrieved March 15, 2008, from http://www.asha.org/public/hearing/testing/assess.htm.

2. World Health Organization (WHO) (2008).

Grades of hearing impairment. Retrieved March 15, 2008 from http://www.who.int/pbd/deafness/hearing_impairment_grades/en/index.

3. National Institute on Deafness and Other Communication Disorders (NIDCD) (April 2007).

Hearing aids. Retrieved March 15, 2008 from http://www.nidcd.nih.gov/health/hearing/hearingaid.asp.

4. Royal National Institute for Deaf People (RNID) (May 2007).

Digital hearing aids. Retrieved March 15, 2008 from http://www.rnid.org.uk/information_resources/factsheets/hearing_aids/factsheets_leaflets/digital_hearing_aids.htm.

5. Ear Science Institute Australia (2006).

Cochlear implants. Retrieved March 15, 2008 from http://www.earscience.org.au/clinics/services/cochlear.php.

6. House Ear Institute (n.d.).

Auditory brainstem implant (ABI). Retrieved March 15, 2008 from http://www.hei.org/news/facts/abifact.htm.

7. E-Michigan Deaf and Hard of Hearing People (2002).

Hearing assistive technology. Retrieved March 15, 2008 from http://www.michdhh.org/assistive_devices/hearing_assistive_tech.html.

8. Rhoades, Ellen. (December, 2007).

Auditory-verbal training. Retrieved March 15, 2008 from http://www.auditoryverbaltraining.com/.

9. Gloucestershire Total Communication Project (n.d.).

Total Communication. Retrieved March 15, 2008 from http://www.totalcommunication.org.uk/.

10. Help Kids Hear. (August, 1997).

Communication Strategies - Total Communication. Retrieved March 15, 2008 from http://www.helpkidshear.org/resources/education/comm/total.htm.

11. Oxford University Auditory-Verbal Programme. (2000).

Auditory Verbal UK. Retrieved March 15, 2008 from http://www.auditoryverbal.org.uk/.

12. Lim, Stacey. (February, 2006).

Auditory-oral. Retrieved March 15, 2008 from http://www.auditoryoptions.org/auditory-oral.htm.

13. Beginnings for Parents of Children who are Deaf or Hard of Hearing. (2008).

Total communication. Retrieved March 15, 2008 from http://www.ncbegin.org/communication_options/total_communication.shtml.

14. National Cued Speech Association. (2006).

Cued speech and literacy: history, research, and background information. Retrieved March 15, 2008 from http://www.cuedspeech.org/PDF/CS_and_Literary.pdf.