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• type |
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• configuration of hearing loss |
Pure-tone audiometry
– behavioral test measure used to determine hearing sensitivity
– test peripheral and central auditory systems
– Pure-tone thresholds (PTT’s) indicate:
• softest sound audible to an individual at least 50% of the time
• plotted on an audiogram
Audiogram
chart of hearing sensitivity
abscissa <=> frequency (range 250-8000 Hz)
- represents most of speech spectrum
- human ear can detect frequencies from 20-20,000 Hz
- children can detect even higher frequencies
ordinate <=> intensity
Intensity: level of sound power measured in decibels;
loudness is the perceptual correlate of intensity.
Hearing level (HL): measured in decibels
(based on the standardised average of individuals with normal hearing sensitivity)
Air Conduction
signal is transmitted through the outer, middle, and inner ear and then through the brain to the cortex.
may be performed using headphones, insert earphones, or sound fields.
Bone conduction
assesses sensitivity when the signal is transmitted through the bones of the skull to the cochlea and then through the auditory pathways of the brain.
bypasses the outer and middle ear.
Bone-conduction oscillator
– small oscillator is placed on mastoid.
– stimulates the bones of the skull, which in turn stimulates both cochleae
Masking
Masking presents a constant noise to the nontest ear to prevent crossover from the test ear.
The purpose of masking is to prevent the nontest ear from detecting the signal, so only the test ear can respond.
Speech Discrimination
ability to repeat correctly an open set of monosyllabic words at suprathreshold intensity.
Word lists are phonetically balanced (PB), ie: the speech sounds used occur with the same frequency as in the whole language.
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PURE TONE AUDIOMETRY - ADULTS |
• Hearing is measured with pure tones through headphones
• loudness of each tone is reduced until patient can just hear the tone.
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HEARING TESTS FOR YOUNG CHILDREN |
Behavioral Observation Audiometry (BOA)
- infants < 7 months of age
- noisemaker testing
Visual Reinforcement Orientation Audiometry (VROA)
• children b/w 7 months & 3 years
• altering frequency and intensity of sounds,
=> child's ability to hear sounds across a range of freq’s
Play Audiometry
• children > 3 years of age.
• child listens to sounds and is taught to make a response every time a sound is heard.
Hearing Levels
10dB to 20dB = Normal range
21dB to 40 dB = Mild hearing loss
41 dB to 55 dB = Moderate hearing loss
56 dB to 70 dB = Moderately Severe hearing loss
71 dB to 90 dB = Severe hearing loss
over 90 dB = Profound hearing loss.
Conductive hearing loss ("mechanical")
blockage or damage to outer +/- middle ear
– perforated tympanic membranes
– fluid in the middle ear system,
– scarring of tympanic membrane.
Sensorineural hearing loss ("electrical")
damage or malfunction of the:
– sensory part (the cochlea) or
– neural part (the auditory nerve)
congenital or acquired
Mixed Hearing Loss
problem in both:
conductive pathway (outer or middle ear)
nerve pathway (inner ear or nerve)
– eg: CHL due to a middle-ear infection combined with a
SNHL due to damage associated with aging
Abbreviations
CNT - Could not test
DNT - Did not test
NR - No response
WNL - Within normal limits
AU - Both sides (ears)
AS - Left
AD - Right
BC - Bone conduction
AC - Air conduction
PTA - Pure-tone average
HL - Hearing level
Tympanometry
Measures compliance of middle ear
Normal (Type A)
Hypermobile TM (high peak – Ad)
Decreased TM mobility (shallow peak - As)
Flat (Type B) – OME or perforation
-’ve middle ear pressure (Type C)
Other tests
Oto-acoustic Emission Testing – OAE
measures function of outer hair cells in the cochlea
they respond to sound by producing a very soft sound of their own called oto-acoustic emission.
Brainstem Evoked Response Audiometry – BERA
(or Auditory Brainstem Response – ABR)
provides information on electrical activity generated in response to sound stimulus along nerve pathway, brainstem, and cerebral cortex
< 6 months old (may be carried in natural sleep)
> 6 months old (under sedation in hospital)
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