Hearing impairment & hearing aids.

From birth to age five, children are. on the "fast track" for acquiring speech and language. As infants and young children build communication skills, they also build stronger and more meaningful relationships with their families. Surrounded by examples of speech used to refer to everyday objects and activities, children learn to produce the same speech sounds to express themselves.

Learning to talk and understand others, then, depends heavily on the ability to hear. For young children whose speech and language development has not kept up with their peers, hearing testing is especially critical. If a child with a hearing impairment receives help and good auditory input at an early age, he or she will have a better chance of learning to use speech and language successfully.

Evaluating hearing

A child's auditory function should be evaluated by an audiologist, a professional who measures hearing and can fit people with different equipment to enhance their hearing. Infants and children from six months to two years of age are tested with a technique known as visual reinforcement audiometry In this test, the child is exposed to animated toys that appear in a window as sounds are presented through a speaker or earphones. The child's hearing can be tested once the child has learned to anticipate the toys' appearance by turning toward the window whenever he or shes hears a sound. Older children may be asked to place pegs in a pegboard or blocks in a bucket when sounds are heard.

Special test procedures can be used with infants or older children who are unable to make voluntary responses to sound. For example, auditory evoked potentials (AEPs) use a computer to measure the brain's response to sound. AEPs--which require that the child be asleep or under light sedation--use electrodes taped to the scalp to measure the brain's electrical activity while sounds are presented.

One component of an AEP evaluation is the auditory brainstem response (ABR) or brainstem auditory evoked response (BAER). Audiologists can use ABRs to assess the hearing of even newborn infants. Any infant at risk for hearing impairments--those with a family history of hearing impairment, very low birth weight, cleft palate and/or certain developmental disabilities--should be tested.

Types of hearing loss

Each sound can be characterized by its pitch or "frequency" (measured in cycles per second--Hertz, abbreviated as "Hz") and by its loudness, or "intensity" (measured in decibels, abbreviated as "dB"). Most speech sounds fall between 250-4000 Hz. Conversational speech is usually at about 60 dB in intensity.

During a heating evaluation, the audiologist plots the quietest sound that an individual can hear at each frequency on a graph called an "audiogram." As viewed on an audiogram, hearing losses may have different shapes. One child may only have trouble hearing high frequency sounds, but hear everything else normally. Another may miss only low-intensity or quiet sounds, but hear fairly evenly across all frequencies. These two listener's would hear the same speech differently. The first child might not be able to hear specific high-frequency speech sounds like "f" and "s," while the second may be able to hear all the speech sounds--but only if they are loud enough. Individuals can have either type of hearing loss, or a combination of the two.

Amplification

Boosting hearing level is called "amplification." When a child's hearing is not within a normal range, parents and professionals work together to decide if amplification will improve the child's ability to understand and use speech. An audiologist will try to provide a hearing aid that will allow the child to comfortably hear the full range of speech frequencies and intensities.

Sensorineural hearing impairment, which involves damage to the inner ear or the auditory nerve, may have an adverse effect on a child's perception of loudness. A child with this type of hearing loss may perceive barely detectable sounds as uncomfortably loud. The audiologist will try to solve this problem by adjusting the aid to control the maximum possible sound produced by the tiny speaker in the hearing aid--also known as the aid's "output." Hearing aids also include circuits that permit audiologists to adjust the output to provide more amplification in the frequency region where the child has the greatest amount of hearing loss.

A variety of amplification devices are available. However, audiologists generally prefer behind-the-ear hearing aids for young children because they can be fine-tuned more easily as additional information about the child's hearing loss becomes available, or if a child's hearing changes over time. Because infants and toddlers grow so fast, in-the-ear and canal-type hearing aids are not typically used--as a child grew, the instruments would need constant re-sizing. With behind-the-ear hearing aids, only the earmold needs to be replaced as a child grows.

Assistive listening devices may also be available in public places. These include FM systems (like small radios) and infrared listening systems, which use the same kind of signal used in TV/VCR remote controls. Designed to overcome the effects of background noise, these devices--common in theaters, churches and schools--transmit a speaker's voice directly to a listener's headphone.

Because of noise levels and bad acoustics in many classrooms, background noise can be a big problem in school. Acoustic ceiling tiles and wall-to-wall carpeting can improve acoustics dramatically. If necessary for a child, these classroom modification, as well as classroom use of an assistive listening device, should be included on the child's IEP.

Hearing aid maintenance

Hearing aids worn by an active toddler are subjected to considerable wear and tear. Because a hearing aid is worn on the body, moisture may affect its delicate electronic circuitry. Hearing aid dehumidifier kits help prevent this type of damage.

It is important to monitor a child's hearing aid(s) on an ongoing basis to ensure optimal functioning. This includes daily battery checks and listening checks using a hearing aid stethoscope that can be purchased from an audiologist. Every three months, have the audiologist take standardized measurements of hearing aid performance. Most hearing aid manufacturers provide a one-year insurance plan for loss or damage. Extended policies can be purchased through the manufacturer or a third-party insurance provider.

Limitations of hearing aids

Parents and professionals should be aware of the limitations of hearing aids. In addition to speech, hearing aids amplify other sounds, such as environmental noise. When amplification is sufficient to amplify speech, "background noise" may interfere and be bothersome to the hearing aid user.

Some children may have such severe hearing impairments that they are able to receive only limited benefit from hearing aids. In such cases, hearing aid use may only provide a child with awareness of environmental sounds like car horns and smoke detectors, or access to certain features of speech, such as changes in loudness or pitch, which may add clues to lip reading.

If a hearing aid is not sufficient to allow a child to develop speech and language, other communication options--such as sign language--should be explored. Cochlear implant surgery is another option that could be discussed with an otolaryngologist (an ear, nose and throat doctor). Cochlear implants have been very controversial within the deaf community. Although some profoundly deaf individuals have become able to discriminate conversational level speech remarkably well after receiving cochlear implants, others receive far less benefit.

Providing hearing aids to a young child is a critical first step. But children with hearing impairments also need early intervention--including language stimulation--during their primary language-learning years. Auditory training can help new hearing aid users learn to pay attention to auditory signals, to recognize differences between auditory signals and to associate meaning with sounds.

For more information, or referral to resources in your area, contact the American Speech-Language-Hearing Association, 10801 Rockville Pike, Rockville, MD 20852, [phone] (V/TTY), [phone] (V/TTY), [phone] (fax).

Joseph P. Pillion Ph.D., CCC-A is a senior audiologist at Kennedy Krieger Institute in Baltimore, Maryland. He has been with the institute for eight years and specializes in audiological management of children with brain disorders.