Deafness is the partial or total inability to hear. People commonly consider a person to be deaf if the person cannot hear well enough to understand speech. But no widely accepted standard of deafness exists, and experts do not completely agree when to use the term. Hearing specialists generally distinguish between deafness and hearing loss. Most people with hearing loss can hear and understand some speech if it is loud enough. But they may be unable to hear other sounds, such as doorbells or high musical notes. In addition, the quality of sounds they do hear may be distorted. Hearing specialists describe hearing loss as mild, moderate, severe, or profound. People may be described as hard of hearing if they have mild to severe hearing loss. Hearing specialists consider people to be deaf when their hearing loss is in the profound range.
Hearing the speech of others is an important part of learning to speak. Deaf children and children with severe hearing loss, therefore, have great difficulty learning to speak. Many deaf people never learn to speak well enough to be understood. Instead, they use sign language and other special methods to communicate.
Hearing loss is a common condition, and millions of people throughout the world are deaf. Although deafness poses special challenges, the condition need not hinder achievement in a wide variety of occupations. The German composer Ludwig van Beethoven, for example, wrote some of his finest music after he became deaf. The American inventor Thomas Edison was deaf much of his life. Helen Keller became a noted author and lecturer despite being blind and deaf.
Types of hearing loss
There are two major types of hearing loss, conductive hearing loss and sensorineural << `sehn` suhr ee NUR uhl >> hearing loss. Some people have a combination of these conditions called a mixed hearing loss.
Conductive hearing loss
results from conditions that interfere with the passage of sound through the outer or the middle ear. Sound normally enters the outer ear and passes down the ear canal to a thin membrane called the tympanum << TIHM puh nuhm >> or eardrum. The eardrum vibrates in response to sound and activates three tiny bones called ossicles << OS uh kulhz >> in the middle ear. Most cases of conductive hearing loss result from diseases that prevent the ossicles from working properly.
Sensorineural hearing loss
involves some defect in the inner ear or the auditory nerve, which leads from the inner ear to the brain. The inner ear contains the actual organ of hearing, called the organ of Corti. This organ converts the vibrations transmitted to the inner ear into electrical signals. The auditory nerve and the structures of the organ of Corti are extremely delicate and may be damaged by a wide variety of factors.
Causes of hearing loss
Hearing loss and deafness can result from a variety of causes. Common causes include aging, disease, injury, birth defect, and exposure to noise.
Aging.
Almost all adults experience some loss of hearing by age 65. About one-third of older adults throughout the world have hearing problems severe enough to seriously impair their ability to communicate. Physicians and hearing specialists call hearing loss in old age presbycusis << prehz bee KYOO sihs >> . They think it is often simply the result of lifelong exposure to noise. But stress and other environmental factors and hereditary factors also have a role in presbycusis. Some hearing specialists think aging also causes changes in the auditory (hearing) system or in the brain that reduce hearing ability.
Environmental factors,
such as accidents and exposure to loud noise, can damage a person’s hearing. A hard blow to the head can cause permanent hearing loss, as can injuries to the eardrum, the bones of the middle ear, or even parts of the inner ear.
Exposure to loud noises can damage the organ of Corti, leading to serious hearing loss. Extremely loud sounds, such as explosions or gunshots, can produce sudden and severe hearing loss. Long-term exposure to other loud noises can gradually cause permanent loss of hearing. People whose work or recreational activities expose them to high levels of noise eventually suffer considerable hearing loss. For example, listening to loud music for long periods can damage hearing. In addition, prolonged exposure to loud noises can cause tinnitus << tih NY tuhs or TIHN ih tuhs >> , a ringing or other noise heard in the ears (see Tinnitus). Physicians recommend that people avoid loud noises or wear earplugs or other ear protection whenever possible to prevent noise-induced hearing loss.
Some drugs, including certain types of antibiotics and pain relievers, can cause structural damage in the inner ear as a side effect. These drugs, called ototoxic drugs, may damage hearing or make existing hearing loss worse. Hearing problems caused by ototoxic medications often go away when the patient stops taking the drug. But sometimes such hearing loss is permanent.
Diseases
cause most cases of conductive hearing loss. The leading such condition, otitis media << oh TY tihs MEE dee uh >> , is commonly referred to as an ear infection. In otitis media, a cold or some other infection spreads to the middle ear and causes it to fill with fluid. The pressure of this fluid reduces the ability of the eardrum and ossicles to transmit vibrations. Otitis media occurs most commonly in early childhood and can lead to serious hearing loss if not treated promptly.
Another major cause of conductive hearing loss is otosclerosis << `oh` tuh sklih ROH sihs >> . In otosclerosis, a bony growth forms around the base of the stapes << STAY peez >> , the ossicle next to the inner ear. This growth prevents the stapes from moving and passing vibrations to the inner ear. Physicians think otosclerosis is hereditary. It may begin to affect hearing at any age but is usually not detected until the teenage years or later.
A disorder of the inner ear called Ménière’s << may NYAYRZ >> disease causes hearing loss, especially among people over 40 years old. This disorder, which affects millions of people, often also disturbs the sense of balance.
Some diseases, including meningitis << `mehn` ihn JY tihs >> can cause sensorineural hearing loss. Meningitis is an infection of the membranes that cover the brain. Other diseases accompanied by a high fever can also severely damage the inner ear and the auditory nerve.
Birth defects
account for many cases of sensorineural deafness. Some inherited defects affect the auditory system at birth or during infancy. Other inherited conditions may lead to hearing loss later in life.
Hearing loss may also result from some factor before or during birth, such as premature birth, the mother’s use of certain ototoxic medications, or an infection during pregnancy. For example, a woman who has rubella—also known as German measles—during pregnancy may give birth to a child with a hearing loss. The rubella can interfere with development of a child’s ears and nervous system, especially if it strikes during the first three months of pregnancy.
Living with hearing loss
People with hearing loss face unique challenges, but medical treatment, special language techniques, and assistive technology can help overcome many difficulties. Many employers have made changes that enable deaf people to communicate more easily with hearing co-workers. A number of colleges and private organizations provide interpreters for the deaf during classes and programs. Many local governments now ensure that deaf and hard-of-hearing people can directly summon emergency services. Governments also help people with hearing loss to communicate in court.
Detection of hearing problems.
Experts called audiologists are specially trained to detect and diagnose hearing problems. An audiologist tests a person’s hearing in a soundproof room using an instrument called an audiometer. Audiometers produce tones of different pitches and volumes to measure hearing sensitivity. Words or sentences spoken by the audiologist are used to measure hearing acuity (sharpness).
Audiologists also have methods to check the hearing of infants and other people who cannot participate in the testing process. These methods involve measuring changes in brain waves and other involuntary responses to sound. Medical professionals often test the hearing of newborn infants within a few days after birth. Many schools test children’s hearing annually.
Medical treatment
can restore hearing partially or completely in many cases of conductive hearing loss. Physicians may use penicillin or other antibiotics to treat otitis media resulting from a bacterial infection. However, antibiotics are ineffective against viral infections, such as colds. In severe cases of otitis media, the physician may make a small incision in the eardrum to drain fluids that have collected in the middle ear. Physicians may insert tiny drainage tubes in the eardrum to treat long-lasting infections.
Medical professionals treat some conductive disorders using surgery. For example, a ruptured eardrum can be repaired surgically. Surgery involving the stapes can restore the ability of the middle ear to transmit sound in patients suffering from otosclerosis. One operation frees the stapes from the bony growth that has trapped it. In another procedure, the surgeon removes the stapes and replaces it with an artificial device.
Most sensorineural disorders cannot be treated medically because damage to the inner ear or auditory nerve is permanent. But a surgically implanted device called a cochlear << KAHK lee uhr >> implant can help some people. A surgeon inserts the device behind the ear and an array of electrodes into the cochlea, the part of the inner ear that contains the organ of Corti. The device converts sounds into electrical signals that are transmitted directly to the auditory nerve. The risks and possible benefits of getting a cochlear implant differ for each individual. Children as well as adults may benefit from cochlear implants.
Some cases of inherited deafness can be treated with gene therapy. In this treatment, medical professionals transfer new genes into a patient’s cells to replace the gene causing deafness. In small trials, gene therapy has given deaf people the ability to hear. But regulatory agencies have not yet approved the treatment for general use.
Special language techniques.
Many people who are deaf or hard of hearing use lip reading and manual communication to help them communicate. Lip reading, also called speechreading, involves understanding what is said by watching the movements of the speaker’s mouth, face, and body. In manual communication, people talk primarily with their hands.
Manual communication usually involves both finger spelling and sign languages. In finger spelling, a different hand signal represents each letter of the alphabet. In sign languages, hand signals stand for objects and ideas. Sign languages are used throughout the world in the same rich variety as spoken languages. Major sign languages used in English-speaking countries include American Sign Language, also known as ASL; British Sign Language; and Signed English.
Deaf people use manual communication to converse with people who understand finger spelling and sign language. They also communicate by speaking and speech reading or by writing. Some use a method called cued speech, which combines hand signals and facial movements to represent the sounds of spoken words. In addition, deaf people may use professional interpreters who can translate between speech and manual communication.
Assistive technology.
Many deaf and hard-of-hearing people use electronic hearing aids to amplify sound. A hearing aid converts sound to an electrical signal, amplifies the signal, and then changes it back into sound inside the ear. Most modern hearing aids use a technology called digital signal processing. Digital processing converts the sound to a numerically encoded signal and uses mathematical formulas to modify the signal, making it more useful to the user. For example, the processing can separate background noise from speech. An audiologist can recommend the proper hearing aid for a particular patient.
Some deaf people use other sensory aids in their daily lives. Many such devices use visual, audible, or vibrating signals to alert deaf and hard-of-hearing people to sounds they might otherwise miss. Visual signals are the most common alerting devices. They include lights that flash when a telephone, doorbell, or alarm clock rings. Many smoke detectors also have light signals. Audible devices, including extremely loud sirens or telephone bells, may be useful for people with mild or moderate hearing loss. Vibrating devices signal a deaf person by shaking a chair or mattress. Deaf and hard-of-hearing people may also wear pagers that vibrate when receiving a signal. Signal dogs, also known as hearing ear dogs, are trained to assist people who are deaf. These dogs alert their owners to specific sounds, such as alarms or doorbells.
Deaf individuals can make and receive telephone calls using a special device called a Telecommunication Device for the Deaf (TDD). A TDD connects to a telephone line with a modem, an electronic device that enables computerized devices to transmit and receive information over a telephone network. Both the caller and the person receiving the call must have a TDD. The message is typed in at the caller’s TDD and typed out at the TDD on the receiving end.
Some countries have telephone relay services. Relay services enable a deaf person using a TDD to communicate with a person using an ordinary telephone. The person placing the call contacts a relay service operator, who then contacts the other party. Using special equipment, the operator relays the conversation word for word between the parties.
A system called closed captioning helps viewers with hearing loss watch television. In closed captioning, printed captions that present the dialogue and sound effects appear on the screen during programs. Closed captions are invisible until a decoder makes them appear on the TV screen. Closed captioning is available in Australia, Canada, the United Kingdom, the United States, and certain other countries around the world.
Education.
Many deaf children receive their elementary and high school education in special schools or in classes with specially trained teachers. Hard-of-hearing children may attend special classes or enroll in regular classes and obtain expert assistance as needed. Many deaf and hard-of-hearing children are mainstreamed—that is, placed in classrooms with nondeaf children.
Educators use three main methods to teach deaf children to communicate: (1) the oralist method, (2) total communication, and (3) sign communication. In the oralist method, children are taught to speak and to speech read. In total communication, they learn manual communication as well as speech and speech reading. Sign communication focuses on manual communication.
Some educators favor sign communication because learning to speak can be extraordinarily difficult for deaf children. Supporters of the oralist method, on the other hand, claim that children who rely solely on manual communication will never develop their potential to communicate with the speaking world. Supporters of total communication believe that deaf children should learn all possible means of communication and decide which methods best meet their needs.
Teaching deaf children to speak requires special techniques. Nondeaf people learn to talk by hearing others talk. But deaf children must use sight and touch to experience spoken words. They watch their teacher make a sound. They also touch the teacher’s face and throat to feel the vibrations and the flow of breath involved in making the sound. Then they try to produce the same vibrations and breath effects themselves.
Many colleges and universities can accommodate the needs of students who are deaf or hard of hearing. In addition, some institutions of higher learning are specifically designed for students with hearing loss. For example, Gallaudet University, in Washington, D.C., is a leading liberal arts college for deaf and hard-of-hearing people. The National Technical Institute for the Deaf in Rochester, New York, accepts only deaf students. The school serves as an international model for educating and preparing deaf and hard-of-hearing students for careers in technology-related professions. The School for the Deaf at the University of Tsukuba in Japan, founded in 1875, is supported by the Japanese government.
Treatment of hearing loss and appropriate education can prepare deaf people to achieve almost any goal in life. But some deaf people have difficulty finding jobs suited to their education and abilities. Many organizations promote the education, training, and employment of deaf people, including the Alexander Graham Bell Association for the Deaf and Hard of Hearing, the Australian Association of the Deaf, the British Deaf Association, the Canadian Association of the Deaf (Association des Sourds du Canada), and the (U.S.) National Association of the Deaf.
Deaf community and culture.
Deaf people have created a network of agencies, churches, clubs, publications, and other resources that meet their special needs. This network of relationships and resources is commonly called the deaf community. Some deaf people regard their deafness as an important part of their identity and function almost exclusively within the deaf community. A number of these people consider themselves culturally deaf. Some members of deaf culture prefer to call themselves Deaf with a capital D to show their commitment to the deaf community. 
Most of the culturally deaf are people who lost their hearing in infancy or early childhood. Many deaf children become involved in deaf culture as they enter special schools where their classmates are also deaf or hard of hearing. This communication environment gives deaf and hard-of-hearing students freedom to focus on learning and to interact easily with students and teachers. Like other people, many deaf people find it more enjoyable and rewarding to relate to others who are fluent in a common language. Many deaf people prefer to communicate using ASL. Culturally, many deaf people take great pride in their lack of hearing and do not consider themselves disabled. They see outdated beliefs and practices as the principal barriers faced by deaf people.
The deaf culture movement in the United States gained strength in a 1988 protest at Gallaudet University. Students and faculty struck to protest appointment of a nondeaf woman as the school’s president. The appointee resigned under pressure, and the American educator I. King Jordan was selected as Gallaudet’s first deaf president.
