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Hearing is one of the five senses and it is required to develop normal speech and language. There are two aspects to communication – the ability to understand what others are saying and the ability to communicate to others, being predominantly through speech. Hearing is required for both of these aspects of communication.
A hearing loss can either be something that you are born with, or a congenital hearing loss or it is something that you acquire after birth, an acquired hearing loss. The incidence of congenital hearing loss is 2-3 per 1000 live births. Due to the large impact a congenital hearing loss can have on an infant’s or child’s development, most infants have a hearing screening before they are discharged from hospital at birth. This captures the majority of congenital hearing losses.
However a child can acquire a hearing loss after birth. The term acquired or congenital only refers to the point in time that they contract the hearing loss, it does not refer to the cause of the hearing loss.
There are many potential causes of acquired hearing losses, including but not limited to: genetic disorders, middle ear infections, viral infections, meningitis, noise exposure and certain medications. Acquired hearing losses maybe temporary or permanent – either way they usually require treatment and often rehabilitation.
Hearing loss, congenital or acquired, can range from a mild to a profound impairment. Many people think that hearing is graded as normal or deaf. They may also think that the child is hearing normally if he or she is responding to sounds or voices. But there are many subtle graduations between normal hearing and deafness and therefore a child’s hearing loss may not be evident or obvious. For example, it is common for a child with a moderate hearing loss to develop speech and language and yet miss over half of what is being said. They may understand what you are saying when you use gestures, or are standing close to them. They will be able to communicate with words, but people who are not used to their speech may have difficulty understanding what they are saying, or, as language becomes more complex, they are unable to pick up the words or concepts. They will often reach a point where advancement stops until the hearing loss can be detected and intervention begins.
It is well established that the earlier a hearing loss is identified and consequently treated or intervention occurs, the lower the impact the hearing loss has on speech and language development.
How is hearing tested in infants and children?
Hearing loss can be accurately measured and identified in infants as young as a few hours old. There are a number of tests that an Audiologist can use to determine hearing. The test/s chosen mainly depend on the child’s age and their ability to understand directions.
Auditory Brainstem Response (ABR)
Auditory Brainstem Response or ABR is a physiological measure of the brainstem’s response to sound. It is an objective test, which means that it isn’t dependent on the child’s responses. It tests the integrity of the hearing system from the ear to the brainstem. The test can be performed on any age of infant (from a few hours of age), child or adult. The test is performed by placing a few electrodes on the infant’s or child’s head to measure the auditory or hearing nerve firing in response to a variety of sounds that are presented to the child or infant through small earphones. The Audiologist can present different pitches or frequencies of sound and different loudness or intensity, thus enabling the determination of the softest levels at which the child’s hearing system responds. The test is extremely reliable in detecting mild, moderate, severe and profound hearing losses, regardless of the cause. It also provides information that is ear specific and identifies the site that the difficulty is arising from in the hearing system.
The main limitation of the test is that the child needs to be still and quiet, and preferably asleep. Our client liaison officers will talk to you about the best way to prepare your infant or child for this test when you are booking the appointment.
Otoacoustic Emissions
The second type of test utilised to objectively test hearing is Otoacoustic Emissions or OAEs. An OAE measures the acoustic response produced by the inner ear or cochlear in response to a sound stimulus. The test is performed by placing a small probe that contains a microphone and speaker into the infant’s or child’s ear and as the child sits quietly, sounds are generated and the responses back from the cochlear are recorded. When normal ear function is present, the emission is present and therefore they have “passed” the test. The main limitation of OAE is that it cannot determine between degrees of hearing loss (mild, moderate, severe or profound) nor the site in the hearing system where the difficulty lies. Because of this it is usually used in conjunction with other tests, like ABR or audiometry.
Audiometry
Audiometry measures the hearing system using a behavioural response from the infant, child or adult. What type of audiometry test is used depends on the developmental age of the child.
Visual Reinforcement Orientation Audiometry or VROAVisual Response Orientation Audiometry
Typically a child from 9 months of age can perform a VROA assessment. This is when a child is “conditioned” to turn his or her head in response to a sound presented. They are “conditioned” by a puppet show. See the images below to demonstrate.
VROA is an accurate means of determining degree of hearing loss and in many cases the site of the damage in the hearing system. However it cannot accurately determine ear specific results, but instead it gives results that predict hearing for the “better ear”. This test is often done in conjunction with OAE or tympanometry for more conclusive ear specific results.
Play Audiometry
When a child is able to tolerate headphones and more complicated comprehension tasks, usually by the age of 3, play audiometry is used. The child is presented with ear specific, frequency specific and intensity specific sounds via headphones and is taught or conditioned to respond in a certain way (usually using a game or pegs or marbles). For example, a child is taught to hold a peg next to his or her cheek, when they hear the sound, they place the peg in the peg-board. The test is reliable and accurate in determining the degree or hearing loss, ear specific information and site of difficulty in the hearing system. The results obtained in this test are often as detailed as an adult assessment.
Tympanometry or Impedance Audiometry
Most audiology assessments will include an evaluation of the middle ear system. This test is called Impedance Audiometry or Tympanometry. The middle ear system is the space behind the eardrum and provides the connection to the nose and throat. It is a common site for ear infections particularly in children, often referred to as glue ear or otitis media.
Tympanometry is an objective test which is performed by inserting a probe in the ear canal, creating a vacuum-tight seal, producing pressure change in the ear canal, and measuring the movement of the eardrum in relation to this pressure change. This test can confirm problems such as fluid behind the ear drum, a hole or perforation in the eardrum, congestion in the eustachian tube or other middle ear abnormalities (such as stiffness in the middle ear bones).
The test is fast (few seconds), accurate and not painful.
When a loud sound is presented to a healthy ear, the eardrum will contract, a sort of built-in hearing protection mechanism (although it's not very effective). This contraction of the eardrum is called the acoustic reflex. The absence of this reflex can further confirm problems of the middle ear, or may help to identify or confirm a hearing loss. Acoustic reflexes are typically evaluated concurrent with the tympanogram.
Impedance Audiometry does not test hearing, it assesses the middle ear function and therefore is always used in conjunction with other tests.
If you are concerned about your child’s hearing, speech or language development, talk to your doctor and ask for a referral to The Neurosensory Unit for a hearing assessment. A complete assessment usually takes no more than 30 minutes and provides you with peace of mind. Your doctor doesn’t need to specify the test/s required, the Audiologist will determine the tests needed dependent on your child’s ages and the concerns and factors presented.