ing aids must learn to consciously filter unneces-
sary noise and sounds. In natural hearing, the
structures of the ear and the BRAINwork in close
integration to receive, transmit, and interpret
sound waves. Hearing aids disrupt that integra-
tion. Sound interpretation becomes a conscious
activity, though with practice it becomes auto-
matic. It takes concentration and focus to partici-
pate in ordinary conversation, and many people
find the effort tiring even when they become pro-
ficient at it. However, most people find the effort a
reasonable trade-off for the return of some hear-
ing ability.
See also COCHLEAR IMPLANT; QUALITY OF LIFE; SIGN
LANGUAGE.
hearing loss The diminishment of hearing abil-
ity. Hearing loss can be temporary or permanent,
sudden or progressive, unilateral (affect only one
EAR) or bilateral (affect both ears), partial or pro-
found (total), congenital or acquired. There are
two kinds of hearing loss: sensorineural (NERVE)
and conductive. About 28 million Americans have
some level of hearing loss; 30 percent of them are
over age 65 and 20 percent are under age 18.
About 1 in 1,000 infants born in the United States
each year has a congenital hearing loss.
Though there are numerous dimensions to
hearing, audiologists measure hearing loss in
terms of sound intensity. Healthy human hearing
perceives tones between frequencies of 500 Hz
(very low) and 4,000 Hz (very high). AUDIOLOGIC
ASSESSMENT measures the intensity of sound
required to hear tones at certain levels within the
range of normal hearing and reports deviations in
decibels (dB) of loss. Hearing loss begins when the
level of loss reaches 16 dB. Health experts classify
hearing loss greater than 90 dB as profound; at
this level the ability to hear the normal sounds of
everyday activities is lost. Though profound hear-
ing loss can occur in only one ear, the term typi-
cally refers to lack of hearing in both ears. Most
health-care providers use the American Speech-
Language-Hearing Association (ASLHA) classifica-
tion system for assessing the degree of hearing
loss.
Hearing loss may result from damage (congeni-
tal or acquired) to the nerves and related struc-
tures of the inner ear that receive and transmit
sound signals to the BRAIN; this is sensorineural
hearing loss. It accounts for 90 percent of all hear-
ing loss and is usually permanent. Hearing loss
also may result from circumstances that prevent
sound waves from traveling through the outer
and middle ears; this is conductive hearing loss
and is often correctable with medications or sur-
gery. Temporary conductive hearing loss is com-
mon, especially in children who have middle ear
infections (OTITISmedia). Congestion due to COLDS
and allergies is a common cause of temporary con-28 The Ear, Nose, Mouth and Throat
DEGREE OF HEARING LOSSClassification Level of Loss Loss Threshold
minimal (slight) 16 to 25 dB ticking of a watch, normalBREATHING
mild 26 to 30 dB hum of electrical appliances
moderate 31 to 50 dB falling rain, whispering, residential neighborhood noise, library, typical
office, normal voice of a child
moderately severe 51 to 70 dB normal conversation, washing machine, sewing machine, vacuum
cleaner, birds, freeway traffic, normal television volume
severe 71 to 90 dB telephone ringing, alarm clock, doorbell, city traffic, noisy restaurant,
flushing toilet
profound 91 db or greater hair dryer, small power tools, crying infant, shouting, police/fire/medical
aid siren