Demographics of Hearing Loss (National Center
for Health Statistics, 1994)
Most common physical disability
24 million Americans have some degree of
hearing loss
2 million have significant hearing loss
(deaf)
22 million have limited loss of hearing
(hard of hearing)
3 million children have hearing
loss
50,000 are deaf
2.5 million are hard of
hearing
Age 2 - 75% of all children experience a
temporary hearing loss due to middle ear infection (otitis
media), most common disease in early childhood.
Elderly individuals have hearing loss due
to the aging process
25% - 65 to 74
40% - 75 and above
Terms
Congenital Loss - one that is present at
birth or occurs during birth process
Acquired loss - one that occurs following
birth
Prelingual Loss - loss that develop before
the development of spoken speech
Postlingual Loss - one that occurs after
development of speech
Process of Hearing
Sound waves travel to listener's ear where
they activate the hearing mechanism. Waves are converted into
nerve impulses that travel to listener's brain and
decoded.
Physics of Sound
Acoustics is the study of sound
Sound consists of disturbances of a
medium due to a vibrating source (vf)
Vibrations occur in cycles, the number
of times a cycle of vibration repeats itself in a second is
the frequency of vibration.
A cycle consists of one compression
and one rarefaction within a second
Hertz - a cycle of vibration is know
as Hertz (Hz)
100 Hz means that 100 cycles of
compression and rarefaction occur in 1
second
Intensity is related to amplitude, which
is the extent of displacement of molecules in the to-and-fro
movements.
Greater the displacement, the higher
the intensity of sounds.
Movements of diaphragm of speaker
illustrate the concept of amplitude
Greater movement of speaker's
diaphragm when sound is increased.
Psychoacoustics is the study of sensory
experiences of sound
Pitch is the perceptual correlate
determined by frequency of vibrations
Loudness is the perceptual correlate
determined by intensity of sound signal
Measures of Hearing
Sensitivity of ear is measured in terms
of a unit called decibel (dB), it is based on a logarithmic
scale.
Lowest intensity of sound needed to
stimulate the auditory system is called Hearing Level
(HL)
Otosclerosis - bony growth that
becomes rigid and prevents movement
Disease of middle ear bones
(particularly stapes)
May be inherited
More common in women
(pregnancy may aggravate condition)
Sensorineural Hearing Loss - sound is
conducted to inner ear, but hair cells in cochlea or
acoustic nerve may be damage, therefore neural impulses
are not transmitted to brain
Characteristics
permanent hearing loss
varies from mild to
profound
due to inner damage, bone
conduction is impaired
may have difficulty hearing
himself
loss is not same across all
frequencies
tendency for higher frequencies
have greater loss
acquisiton of speech and
language may be affected pending
severity
Causes
Prenatal
Ototoxic damage due to
medications during 6th and 7th week of
preganancy can cause cochlear damage in
fetus
Antibiotic drugs of mycin
family (streptomycin, kanamycin,
neomycin)
Noise (loud music, noisy toys,
firecrackers, explosives)- prolonged expose to
intense noise may cause damage to cochlear hair
cells.
Noise induced loss worst
between 3000 Hz and 6000 Hz
Infections
Maternal rubella - cause of
fetal cochlear damage
Meninngitis - inflammation
of meninges due to viral infection
Syphilis (maternal),
anoxia
Tumor
Old Age
Presbycusis - effect of
aging
Mixed Hearing Loss - involvement of
both middle and inner ear components
Assessment of Hearing Loss
Audiology is the study of hearing, its
disorders, and the measurement and management of hearing
disorders
Audiologist has training in the
assessmenet of hearing disorders and rehabilitation of
individuals with hearing impairment.
Hearing Loss Simulator
Audiometer is electronic instrument used
to assess hearing
Presents pure tones, noise and
speech
Presents pure tones at various
frequencies at various intensity levels
Pure tone Audiometry
Pure tone hearing test is used to
determine threshold of hearing
Threshold is an intensity level at
which a tone is heard at 505%of the time