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Hearing Loss: An Overview


The early identification of a hearing problem is essential to ensure appropriate linguistic and social development of a child with a hearing loss. Parents are advised to have their newborns receive their first hearing tests before they are 1 month old. Babies who are born deaf have a better chance of learning how to use language if the hearing loss is found immediately after they are born and if they can learn a spoken or signed language as early as possible.

Hearing loss is very complex, and historically, definitions of deafness or distinction between deafness and hard of hearing have been problematic, a point that has been noted by many researchers (Morsh, 1936; Myklebust, 1964; Schein & Delk, 1974; Schildroth & Karchmer, 1986). Intensity, frequency, and tone of sound are all involved in determining hearing loss. The definition of deafness has varied in research studies according to educational or medical classifications. A distinction between deaf and hard of hearing was primarily determined by researchers using information from the schools or agencies that have provided participants for research studies. In recent years, the cultural definition has resulted in the term, Deaf, with an uppercase D to refer exclusively to a cultural identity for those who use sign language as their primary means of communication. The field of Deaf Studies has emerged to examine the social and cultural context of the lives of Deaf people (Andrews, Leigh, & Weiner, 2004).

The term deaf is applied to those whose hearing loss is so severe that they are not able to fully acquire spoken language without some assistive device such as a hearing aid or cochlear implant. There was a trend in the 1980s toward the use of hearing-impaired as an umbrella term, which included those who are hard of hearing (have a hearing loss, with residual and/or improvable hearing) and those who are deaf (Commission on Education of the Deaf, 1988; Stewart, 1986). The unit of measurement that expresses the intensity of sound is the decibel (dB). A person within the normal range can hear sounds ranging from 0 to 14 dB. Degree or amount of hearing is most often measured with an audiometer that emits a constant tone. Pitch and quality are not addressed with this method, making sound intensity the only assessed variable. The most commonly used audiometer has been the Pure Tone Audiometer. This device takes the pure tone average from the standard audiometric testing frequencies of 500, 1,000, and 2,000 Hertz. This is also called the speech frequency average (Lloyd & Kaplan, 1978).

Nicolosi, Harryman, and Kresheck (1989) define residual as the part of a function that remains after a portion has been removed. Therefore residual hearing is the ability to hear above that which has been lost. Hearing level is denoted in number of decibels required for an individual to receive sound above audiometric zero, which is the level required for the average normal ear to receive sound. Hearing loss is defined in degrees, the categories of which usually range from slight to profound.

The Gallaudet Hearing Scale (Schildroth & Karchmer, 1986) is based on the ability to hear and understand speech. The Committee on Conservation of Hearing Loss developed a similar scale on inability to hear speech and equated these levels with better-ear average dB hearing loss levels. A summary of these scales is, (a) can hear soft speech, 26 dB loss (or less); (b) difficulty understanding whispered speech, 26-40 dB loss; (c) can hear some shouted speech, 41-70 dB loss; (d) understand shouted or amplified speech, 71-90 dB loss; and (e) cannot hear any speech, 91 (or greater) dB loss (Schildroth & Karchmer, 1986). Though these classifications can vary somewhat, the preceding hearing loss scale may be matched by the following descriptions: normal, mild, moderate, severe, and profound (Lloyd & Kaplan, 1978). The 70 dB level is the generally accepted point for distinguishing between hard of hearing and deafness.

In reality, no two individuals have the same pattern of hearing, even within these categories. Someone who has a 90 dB or greater hearing loss has difficulty with hearing most sounds. The activities sponsored by the USA Deaf Sports Federation are open to those individuals with a hearing loss of 55 dB or greater in the better ear. The use of hearing aids is prohibited in competitions.

Types of Hearing Loss

There are three types of hearing loss: conductive, sensorineural, and a combination of conductive and sensorineural. In conductive hearing loss, the outer and/or middle ear is affected. This loss can be caused by problems with the eardrum and/or the auditory ossicles that conduct the sound vibrations; it can sometimes be corrected with surgery. These losses are not usually severe and result in hard of hearing. A conductive hearing loss does not usually exceed a 60-dB hearing loss. The inner ear is affected in sensorineural hearing loss; this is caused by damage to the cells and nerve fibers that receive and transmit sound (Bevan, 1988). A greater than 60-dB hearing loss is usually sensorineural in origin. Meningitis often destroys the labyrinths and semicircular canals, causing total hearing loss and balance disturbance.

Senior citizens typically demonstrate the mixed type of hearing loss with conductive and sensorineural deficiencies. Rotational turning of an individual is a technique for determining whether there is semicircular canal impairment. Rotational turning on a vertical axis will elicit an involuntary rhythmic oscillation of the eyes, termed nystagmus. An abnormal or lack of rhythmic oscillation of the eyes indicates semicircular involvement. Previous research studies determined that those with semicircular impairment experience more difficulties with balance (Boyd, 1965; Gayle, 1977; Myklebust, 1964).

Etiology

Causes of hearing loss are usually subdivided into prelingual and postlingual categories. Prelingual causes include premature birth, complications at birth, heredity, maternal rubella, and cytomegalovirus (CMV). Primary post-lingual causes are meningitis and otitis media (infection or inflammation of the middle ear). Maternal rubella plagued the population with cyclical epidemics until a rubella vaccine was instituted in 1969. By the mid 1980s, rubella-caused hearing loss declined by 10% to 20%, resulting in a decrease in the severity of hearing loss (Schildroth & Karchmer, 1986). With vaccines, hearing defects from mumps and measles have almost disappeared. Hearing loss incurred through Rh incompatibility has declined, possibly due to improved transfusion techniques. Postnatal trauma-caused hearing loss should also continue to decline with improved neonatal care. Heredity and meningitis etiologies will probably remain about the same. Even though 90% of children who are deaf have hearing parents, approximately 30% have a deaf or hard of hearing relation (Moores, 1996). It is likely that hearing loss due to otitis media, pregnancy complications, birthing trauma, infection, and high fever will continue to exist (Schildroth & Karchmer, 1986).

Some sexually transmitted diseases are known to cause deafness. With an expansion of sexually transmitted diseases, there is likely to be an increase in deafness from this cause (Bess, 1988; Vernon, 1981). Sexually transmitted diseases can cause sensorineural hearing loss. Cytomegalovirus is the most common cause of congenital virally induced deafness, but herpes simplex, syphilis, and human immunodeficiency virus can also cause deafness (Bess, 1988; Vernon, 1981).

Modern medicine has dramatically increased the survival rate of traumatic births and head injuries, both of which can cause sensorineural hearing loss. Despite better reporting mechanisms, the highest single percentage of etiological categories is still the "unknown" (or unclassified) group (Bess, 1988; Schildroth & Karchmer, 1986). Unknown causes account for 33% of children with prelingual hearing loss (Center for Assessment and Demographic Studies, 1998). Also, the age of onset of hearing loss in 95% of Deaf children and youth is prelingual, before the age of 3 (Commission on Education of the Deaf, 1988).

Communication

Productive and receptive linguistic abilities have a profound effect on Deaf individuals. Communication barriers can have an impact on the entire sphere of human relationships. As a consequence of communication problems, Deaf individuals historically had restricted experiences influencing social, vocational, educational, recreational, and psychological/emotional development (Sims, Walter, & Whitehead, 1982).

The history of Deaf education indicates considerable controversy in communication methodology. The appropriate method of communication for a Deaf individual depends on the degree of hearing loss and age of onset. Often the method used depends on hearing ability and convictions of parents. There are three basic modes of Deaf communication: oral, manual, and total communication. The oral method attempts to integrate the Deaf individual into the hearing society as fully as possible and promotes instruction in spoken English, speech reading, and amplification of residual hearing. The manual mode uses one of the sign languages (American, Pidgin, or Manual) for communication. Total communication is multimodal and consists of oral, signed, and written communication (Sims et al., 1982). Total communication has gone somewhat out of favor (Schirmer, 2001) since using every communication technique and mode available is often unrealistic. There is general consensus that children who are deaf who do not receive help to communicate and learn either a spoken or sign language cannot as effectively develop their thinking, communicate, solve problems, or explore and interact with the world. Overall, there have been many technological and medical advances that have improved communication options. However, there are still distinct communication barriers for Deaf persons in social contexts with people who hear but who do not sign (Ellis & Stewart, 2005).

Educational Trends

Since Public Law 94-142 (1975), deaf education professionals have not embraced integration. In contrast to other disability areas, professionals in deaf education have believed that integration of Deaf children in general education classrooms had limited benefits and were not going to meet all the needs of Deaf children. Forced inclusion has been viewed as a distinct problem for the Deaf community.

Prior to PL 94-142, individuals who were prelingually deaf were educated in residential schools while those who acquired deafness between 12 and 18 years of age tended to be placed in general education (Schein & Delk, 1974). This traditional method changed somewhat with the advent of PL 94-142. There was some evidence that the numbers of Deaf children in public education fell in the 1980s. Schildroth and Karchmer (1986) note that enrollment in residential schools for the deaf in the 1980s fell in proportion to enrollment in general education. The Commission on Education of the Deaf (1988) indicated that 1985-86 enrollment in special schools was down by approximately half compared to 1977-78, while Deaf student participation in both special education and general education increased slightly.

Approximately 1.3% of all school-age children ages 6 to 21 who received special education services during the 1996-97 school year were in the category of hearing-impaired (National Center for Education Statistics, 1999). The 25th Annual Report to Congress in 2005 on the Implementation of the Individuals with Disabilities Education Act (IDEA) provides the most recent update on numbers of children with hearing loss receiving education services. This report indicates that 7,475 children 3 ages to 5 received services under IDEA and 71,821 children ages 6 to 21 were served in school year 2001. In this group of children ages 6 to 21, 60,146 with hearing loss were educated in local schools in 2001. With respect to education placement, 29,998 children spent less than 21% of time outside the regular class, 14,186 children spent between 21% and 60% of time outside the regular class, and 15,962 children spent more than 60% of time outside the regular class. There were 5,873 children in public residential locations and 391 in private residential facilities. This data validates that Deaf children receive their education in public schools (Moores, 2001).

Cochlear Implants

A cochlear implant is a small electronic device that works by providing direct electrical stimulation to the auditory nerve, bypassing the usual transducer cells that are absent or not functioning in the cochlea. Implants are multi-electrode arrays that provide a number of independent channels of stimulation. A cochlear implant is a surgical procedure. The current generation of intro-cochlear, multi-channel implants with spectrally based speech processors provides a substantial improvement over the previous generation of devices. Children at least 2 years old and adults with profound deafness are candidates for implantation. The greatest benefits have occurred in post-lingual deaf adults whereas cochlear implants in pre-lingually deaf adults have provided more limited improvement in speech perception, although offering important environmental sound awareness. In children, gradual steady improvement in speech perception, speech production, and language has occurred.

For children, cochlear implants coupled with intensive post-implantation therapy can help young children to acquire speech, language, developmental, and social skills. Cochlear implants are still controversial and the Deaf community views deafness as a cultural component, not a disability. In addition, there are concerns about the use of implants during physical activity (Dummer & Ellis, 2003), including sports equipment that may interfere with operation and behind-the-ear transmitters that may fall off during activity.

Communication Skills of Parents

More than 90% of Deaf children have hearing parents and of the children in educational programs for the Deaf, only 4% to 6% have Deaf parents (Regional and National Summary Report, 2001). There is evidence that Deaf children of Deaf parents have better academic, linguistic and social characteristics than Deaf children of hearing parents. This finding is based on Deaf parents having superior sign-language skills and more effective overall communication strategies than those exhibited by hearing parents. Liberman, Volding, and Winnick (2004) found no difference between motor development of children with Deaf parents and those with hearing parents. One critical area of communication relates to family medical history. Enhanced communication will provide health benefits for Deaf children. Families should be encouraged to discuss health issues and devise appropriate preventive health strategies based on medical history.


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