PURE TONE AUDIOMETRY
Pure tone audiometry measures hearing sensitivity in each ear. Sounds are presented at different frequencies
(or pitch) at reducing levels of loudness. The softest tone heard is known as the hearing threshold level and is
recorded on an audiogram.
From this we construct a graph or audiogram which shows us if there is a hearing loss and assists in determining
what part of the ear
is damaged. This is
essential in the diagnosis
of hearing loss and for
the prescription of
Speech audiometry is used to determine the weakest intensity at which an individual can recognize words, or
to measure the clarity of words when they are heard at a comfortable loudness.
Impedance tests are measurements of middle ear function and assess the integrity of the middle ear system and the eustachian tube.
These tests include
reflexes and eustachian
OTOACOUSTIC EMISSIONS (OAE) TEST
This brief test is performed with a sleeping infant or an older child who may be able to sit quietly. A tiny probe
is placed in the ear canal, then many pulse-type sounds are introduced and an "echo" response from the outer
hair cells in the inner ear is recorded. These recordings are averaged by a computer. A normal recording is
associated with healthy outer hair cell function and reflects normal hearing, although in some cases the
hearing loss may be due to problems in other parts of the hearing pathway.
Tympanometry is not a hearing test but a procedure that can show how well the eardrum moves when a soft
sound and air pressure are introduced in the ear canal. It's helpful in identifying middle ear problems, such as
fluid collecting behind the eardrum.
Physiologic tests are not hearing tests but are measures that can partially estimate hearing function. They're used for children who can't be tested behaviorally (due to young age, developmental delay, or other medical conditions) and sometimes can determine which function of the auditory system is at fault
AUDITORY BRAINSTEM RESPONSE (ABR) TEST
For this test, tiny earphones are placed in the ear canals and small electrodes (which look like small stickers) are placed behind the ears and on the forehead. Usually, click-type sounds are introduced through the earphones, and the electrodes measure the hearing nerve's response to the sounds. A computer averages these responses and displays waveforms. An infant may be sleeping naturally or may have to be sedated for this test. Older cooperative kids may be tested in a silent environment while they're visually occupied.
Because there are characteristic waveforms for normal hearing in portions of the speech range, a normal ABR can predict fairly well that a baby's hearing is normal in that part of the range. An abnormal ABR may be due to hearing loss, but it may also be due to some medical problems or measurement difficulties.
AUDITORY STEADY STATE RESPONSE (ASSR) TEST
An infant is typically sleeping or sedated for the ASSR. This is a new test that currently must be done in conjunction with the ABR to assess hearing. Sound is transmitted through the ear canals, and a computer picks up the brain's response to the sound and automatically establishes the hearing level.
TESTING INFANTS AND CHILDREN
Pure Tone audiometry is adapted for older children to test their behavioural thresholds. Either visual response audiometry or play audiometry are used with children older than 3 months. As these tests require the child’s participation, results are not used in isolation and are confirmed with the use of a physiological (objective) test battery that does not require a behavioral response from the child. These tests can assess whether sound is being conducted efficiently, or if there is damage to the inner ear or nerve pathways. We also perform tests to determine if the brain is processing what the child is hearing (in order to assess the presence of Central Auditory Processing Disorders).
Hearing tests rely on the use of a piece of equipment known as an audiometer. The audiometer is a relatively simple device which produces sounds at different frequencies and volumes (as designated by the audiologist and standard practises) played to the patient (over headphones). The patient listens to the sounds and registers that he/she heard the sound by means of pushing a hand held button linked to the machine as an input. The sounds are measured in decibel hearing levels (dBHL) – the level at which the patient can hear is registered as his/her hearing threshold. Normal hearing range is defined as 0 to 15dB with categories of hearing loss pegged at levels higher than 20dB are listed below:
Minimal: 16 to 25dB
Mild: 26 - 40dB
Moderate: 41 - 65dB.
Severe: 66 – 95dB
Profound: 96dB and above
Audiogram Showing Levels of Hearing Loss
There are three parts to a basic diagnostic hearing test or audiometry
Pure tone audiometry