Hearing Development and Impairment
Hearing Development and Impairment
Hearing begins in the womb—pregnant women have reported feeling the fetus move in response to loud noises at 31 weeks (7 weeks before full-term delivery). Newborns are sensitive to the location, frequency, pitch, and volume of sounds. Loud sounds startle them, while rhythmic, repetitive sounds tend to soothe them. During the second month of life, they become sensitive to a wider range of sounds, reacting to a variety of medium-range sounds that can affect them differently depending on their mood. (For example, a child at this age may enjoy the sound of a vacuum cleaner when she is feeling happy and become upset by it when she is in an irritable mood.) It has been found that infants can hear higher frequencies than adults can (a fact that may be related to the adult instinct to produce "baby talk" at higher pitches than those of their normal speaking voices). In addition, babies can detect a broad range of pitches and discriminate among different speech sounds (better, in some cases, than adults). At the age of six months, they can tell the difference between sounds that differ as little as 10 decibels in loudness.
Parents can test the hearing of a young infant at home by clapping or making some other loud noise and seeing if it elicits a startled response. By the age of six months, infants will look around for the source of the noise. Hearing should also be evaluated regularly by a
Approximately 1% of all children sustain some degree of hearing impairment, with 2 out of 1,000 suffering profound hearing loss. About 65% of these children are born deaf, and an additional 12% become deaf before the age of 3. A hearing loss delays speech and language acquisition, interferes with cognitive development, and disrupts progress in school. Even with the modern technology and level of health care available in the United States, hearing losses in children sometimes go undetected or unconfirmed for months or even years—significant hearing losses have gone undiagnosed in children as old as six. Early detection and intervention are crucial in preventing or minimizing developmental and educational delays.
Hearing loss is most commonly categorized by which parts of the ear are affected. Conductive hearing loss is caused by a problem in the middle or outer ear that interferes with the conduction of sound to the inner ear, while sensorineural hearing loss involves an abnormality of the cochlea or auditory nerve in the inner ear. Mixed hearing loss indicates a combination of both of these types. Hearing impairments are also classified as prelingual (before a child can learn to speak) or postlingual (after language acquisition has occurred), and genetic or nongenetic (based on whether it is inherited). Yet another way hearing loss is classified is by severity. Normal hearing is generally defined as the ability to hear sounds of 15 decibels (dB) or less. A child with a mild hearing loss can only hear sounds that are between 15 and 40 or 45 dB or louder. At this level of hearing loss, speech and conversation are unaffected, but there is some difficulty hearing distant sounds. A moderate hearing loss means that only sounds registering 40 to 60 or 70 dB can be heard. At this level, the ability to hear normal conversation and form sounds is affected. With severe hearing loss, a child can only hear sounds that register 60 to 90 dB and needs a hearing aid to be able to discern more than an occasional word of conversation. A profound hearing loss is defined as the inability to hear sounds that are under 90 dB, meaning that only very loud sounds—louder than those used in conversation—can be heard. A child with profound hearing loss may hear better with a hearing aid but will still generally be unable to articulate words normally.
The most frequent cause of hearing impairment in children is otitis media, or infection of the middle ear, which is very common in children between the ages of 6 months and 2 years (and can occur in older and younger children as well). Ordinarily it causes a mild to moderate, temporary conductive hearing loss that disappears when the condition clears up. However, persistent or recurrent infections may cause an ongoing moderate hearing loss that can interfere with speech and language development. Common treatment methods for this problem include prolonged low doses of antibiotics and an outpatient procedure called a myringotomy, in which a small tube is inserted through the eardrum to drain fluid and equalize the pressure between the middle ear and the ear canal. Certain physical conditions are associated with conductive hearing loss from middle ear infections. These include cleft palate, which impairs middle ear drainage through the eustachian tubes, leading to conductive hearing loss in 30% of children with this condition; other head and facial abnormalities, such as Treacher-Collins syndrome; and Down syndrome, which is characterized by narrow ear canals that are conducive to middle ear infections. About 80% of children with Down syndrome sustain some degree of hearing loss.
Another cause of conductive hearing loss is excessive build-up of earwax, which can keep sound waves from reaching the eardrum. Earwax, which protects the ear from dust and other foreign matter, is produced by glands in the outer ear canal and normally works its way out of the ear naturally. However, sometimes excessive amounts can build up and harden in the outer ear canal, causing a gradual decrease in hearing and, in some cases, irritating the canal. Earwax can usually be removed at home (with a doctor's instructions) by flushing out the ears with water after using special drops to soften the wax. If necessary, the doctor can remove earwax by suction or with a metal probe.
Sensorineural hearing loss has a variety of causes, including over 70 known genetically inherited conditions, which account for approximately half of all severe sensorineural hearing losses. Problems occurring during birth or shortly afterward (such as asphyxia, where the baby fails to breathe) can cause inner ear or nerve damage. Hearing loss may also result from intrauterine infections during pregnancy, the best-known of which is rubella (German measles) contracted during the first trimester of pregnancy. Other viruses known to cause sensorineural hearing loss include toxoplasmosis, herpes, and cytomegalovirus (CMV). Bacterial infections in infancy (such as meningitis) are another cause of hearing impairment. It is also thought that the noise from incubators may affect the hearing of premature infants.
A variety of hearing aids are available for children. The postauricular, or behind-the-ear, hearing aid fits behind the ear and is connected to a plastic earmold, which is custom-fitted to each child. (These must be replaced frequently in rapidly growing young children.) An older child with sufficient residual hearing can use the less noticeable in-the-ear or in-the-canal hearing aids, in which the entire apparatus fits inside the ear. In addition to these traditional hearing aids, recent technological advances have made several newer devices available. The transposer changes high-pitched sounds inaudible to many hearing-impaired persons into lower-pitched sounds they can hear. Hearing aids that can be programmed by computer are custom-fitted to an individual's particular type of hearing loss. The new device that has received the greatest degree of attention is the cochlear implant, which, attached directly to the cochlea in a surgical procedure, functionally "replaces" the damaged hair cells of persons with sensorineural hearing loss. The implant itself, consisting of electrodes implanted into the cochlea through a hole drilled in the mastoid bone, works together with two external components: a speech processor, which is commonly worn on the belt or carried in a pocket, and a microphone. Unlike hearing aids, which can only help children who have some residual hearing, cochlear implants can help those whose hearing is completely destroyed. Over 1,000 children worldwide have been fitted with these devices. While cochlear implants do not restore full normal hearing, they offer potentially substantial improvement in speech recognition and production, as well the ability to hear and identify common sounds such as car horns and doorbells.
Today a variety of educational approaches are used with hard of hearing and deaf children. A variety of systems, known as oral approaches, utilize spoken rather than sign language for all communication needs. They may rely on lipreading or on the extension of residual hearing made possible by today's powerful hearing aids and cochlear implants, or on a combination of both methods. One of these, the auditory-verbal approach, relies on enhanced residual hearing, teaching children to speak by having them listen to spoken language. Its ultimate goal is to enable children with hearing loss to attend regular schools and participate fully in the life of the hearing world around them. Another method, Cued Speech, supplements lipreading skills with a set of eight phonetically based handshapes. Each handshape represents several combinations of consonant sounds in order to help children learn how words and letters sound. (Vowel sounds are represented by a series of diagrams showing different placements in and around the mouth.) The phonetic mastery made possible by Cued Speech can enable hearing-impaired children to become familiar with a variety of dialects besides their own and learn spoken foreign languages as well.
In contrast to oral methods, the Bilingual-Bicultural (or Bi-Bi) approach treats the hearing impaired as a separate culture with its own language (American Sign Language, or ASL). With this approach, ASL is taught as the primary language and standard English (written only) as a secondary one. In addition, children learn about the history, contributions, and customs of deaf culture, and their parents are encouraged to learn ASL and become active in the deaf community. A contrasting approach that incorporates signing is called Total Communication, which is based on a philosophy of inclusiveness that embraces all forms of communication that can help a hearing-impaired child communicate and learn, including hearing amplification, signs, gestures, lipreading, and finger-spelling. However, unlike the Bilingual-Bicultural approach, Total Communication uses signing systems based on English (collectively referred to as Manually Coded English or MCE) rather than American Sign Language, which is a separate language system distinct from English. Manually Coded English systems include Signed English, Seeing Essential English and its spin-off, Signing Exact English, and Contact Signing (formerly called Pidgin Sign English).
Jeffrey, Lorraine. Hearing Loss and Tinnitus. New York: Sterling Publishing, 1995.
Maxon, Antonia. The Hearing-Impaired Child: Infancy through High School Years. Boston: Andover Medical Publishers, 1992.
Roush, Jackson, and Noel D. Matkin, eds. Infants and Toddlers with Hearing Loss: Family-Centered Assessment and Intervention. Baltimore: York Press, 1994.
Schwartz, Sue, ed. Choices in Deafness: A Parents' Guide to Communication Options. 2nd ed. Bethesda, MD: Woodbine House, 1996.
Alexander Graham Bell Association
Address: 3417 Volta Place, NW
Washington, DC 20007
Telephone: (202) 387-5220
Deafness Research Foundation
Address: 9 E. 38th Street
New York, NY 10016
Telephone: (212) 684-6556
Hearing Aid Helpline
Address: 20361 Middlebelt Rd.
Livonia, MI 48152
Telephone: toll-free (800) 521-5247; (313) 478-2610
National Association for Hearing and Speech Action
Address: 10801 Rockville Pike
Telephone: toll-free (800) 638-8255; (301) 897-8682