How do we test the hearing of babies and children? An audiologist will select from a range of different tests to evaluate your child s hearing. The choice of test depends on the information that is needed about your child s hearing and their age and abilities. If your child has a hearing loss, different tests may be needed to find out where the hearing problem is in the auditory system. There are two main types of hearing tests; behavioural tests and objective (or electrophysiological) tests. Behavioural tests look at the entire auditory system - the sound has to travel right through the auditory system from the ear to the brain before your child behaves in some way in response to the sound. To get results, your child needs to be able to cooperate and respond to sound in a way that can be observed by another person. To find out about hearing in each ear, your child needs to wear insert earphones or headphones during the testing. Accurate behavioural tests can be completed with many babies with a developmental level of about six months of age. For children and babies at a younger developmental level, behavioural results can still provide very useful information, if they can be obtained. Objective tests give information from specific parts of the auditory system, depending on the test and which ear is tested. This information is important to identify where the hearing loss occurs in the auditory system. Objective tests can only provide an estimate of hearing ability. Most objective tests need your child to sit or lie quietly. Some can be performed while your child is asleep. Both types of test are used investigate your child s hearing and to understand the nature of any hearing loss that may be present. Types of hearing tests in this section Behavioural Observation Audiometry (BOA) Visually Reinforced Orientation Audiometry (VROA) Play Audiometry Objective testing 1 / 6
The importance of a test battery Ongoing care Behavioural Observation Audiometry (BOA) Behavioural Observation Audiometry (BOA) is a behavioural test used with babies and children who have a developmental age under six months. Sounds are presented to your baby in a quiet, controlled environment and your baby s responses are carefully observed. Behavioural responses may include being startled by loud noises, stirring from sleep in response to a sound, changes in sucking when a sound is heard or trying to look towards the sound. The best responses can be obtained when a baby is just on the edge of falling asleep. The sounds used for testing young babies need to be complex to attract their interest. Singlefrequency (pure) tones usually do not get any response until they are very loud. An assortment of noisemakers are used, such as crunching cellophane, tiny bells, chimes and bicycle hooters. These noisemakers are known to be either low, mid or high-frequency, or broadband sounds. During testing, the audiologist will check the loudness of the sounds with a sound-level meter. Although hearing levels can t be determined exactly, an experienced audiologist can obtain a great deal of information about your baby s hearing loss and their ability to detect different sound frequencies. The procedure tests both ears at once as your baby doesn t wear headphones. Visually Reinforced Orientation Audiometry (VROA) Once your baby has good head control and can turn towards something interesting, a more advanced behavioural procedure can be used. Visually reinforced orientation audiometry (VROA) involves your child turning towards a certain spot in the room whenever a sound is presented. When your child looks to this location, a light-box lights up to show a puppet or some other visual reward. Your child soon learns that if they hear the sound and turn to look at the light-box, they will see the puppet or other visual reward. Accurate hearing thresholds can be obtained using this procedure. Also, children at this age will respond to more frequency-specific sounds. These sounds can be presented through a speaker, headphones, insert earphones or a bone conductor. For children who wear hearing aids, this procedure can be used to check their aided hearing, although more accurate procedures are usually used to measure and adjust the hearing aids. Most children enjoy VROA and soon learn its rules. This procedure is used from when your child is about six months old until the time when their concentration span is long enough to move on to 2 / 6
play audiometry. Play Audiometry Play audiometry works in a similar same way to pure tone audiometry. Most children will be able to do this from around two and half to three years of age developmentally. Your child will be asked to do something each time they hear a sound: put a marble in a marble race; put a piece in a puzzle; or press a computer keyboard to make something happen. Making a game of the test helps to keep your child s interest and this lets the audiologist gather more test results. This technique can be used with sounds delivered through a speaker, headphones, insert earphones or a bone conductor. For children who wear hearing aids, this procedure can also be used to check their aided hearing, although more accurate procedures are usually used to measure and adjust the hearing aids. Objective testing Objective testing does not require your child to actively participate, but they will need to sit or rest quietly during the test. The objective tests commonly used in audiology are: Tympanometry Otoacoustic Emissions (OAEs) Auditory Brainstem Response (ABR) Electrocochleography (ECochG) Auditory Steady-State Response (ASSR) Cortical Auditory Evoked Potentials (CAEP) and Aided Cortical Asessment (ACA). Tympanometry Tympanometry is not a hearing test but a test of how well the middle ear system is functioning and how well the eardrum can move. The test can be very quick (a few seconds in each ear) provided your child is sitting quietly. A small rubber tip is placed in the ear canal to form an air-tight seal. A little air is pumped into the outer ear canal and sound reflected back from the ear drum is measured. If there is a problem in the middle ear it will usually show up on this test. For example, if there is very little movement of the eardrum, this might indicate that there is fluid behind the drum as a result of a middle ear infection. Middle ear conditions can develop quite quickly so this test is used frequently to monitor to a child s hearing, especially if they already have a hearing loss. Children with abnormal tympanometry results will usually be referred to their health practitioner for medical advice. 3 / 6
Otoacoustic Emissions (OAEs) Otoacoustic Emmisions (OAEs) are tiny sounds given off by a part of the inner ear (cochlea), when it is stimulated by a sound. For this test to work, your child needs to be sitting or lying quietly in a quiet room. OAEs can only be measured if the middle ear is functioning normally, so tympanometry is always checked first. If conditions are right, the OAE test can be completed in a matter of minutes in each ear. A small plug (probe) is placed in your child s ear and a series of very fast clicks is played through the probe. The sound coming back from the cochlea is also measured by the probe and results are displayed on a screen. The OAE results need to be interpreted in the context of other test results. If your child has OAEs present, they are likely to have near-normal hearing in that ear or at the frequencies where OAEs are measured. The exception is where a child has auditory neuropathy. Children with auditory neuropathy can show large, clear OAEs, but other test results will show a sensorineural hearing loss. If a child has a hearing loss greater than about 40 db HL, no OAEs will be measured. The OAE procedure does not cause any pain or discomfort and a young baby can often sleep right through the test. If your baby is older, they might need light sedation for useful results to be obtained. Older children can usually cooperate and sit quietly as needed. Auditory Brainstem Response (ABR) This test might also be referred to as Brainstem Evoked Response Audiometry (BERA). This procedure measures the electrical activity from the nerve pathway between the ear and the brain, in response to sound. Electrodes (small metal disks) are attached to your child s head to record electrical energy that occurs in the auditory brainstem in response to sound. Your child will also wear insert earphones which deliver the special test sounds to one ear at a time. Because the electrical signal picked up by the electrodes is very tiny, the signal must be measured many times at each frequency to get a reliable result. Your baby needs to be asleep or very still and settled to obtain results. If ABRs can be measured, it may be possible to continue testing at softer and softer levels to look for an ABR hearing threshold for a particular sound. This procedure does not cause any pain or discomfort. If your baby is older, they might need light 4 / 6
sedation for useful results to be obtained. Electrocochleography (ECochG) In electrocochleography (ECochG), a very fine electrode is placed through the eardrum into the middle ear and rested against the cochlea. The electrode can then pick up the tiny electrical signals generated in the cochlea in response to special sounds. The electrical activity measured in ECochG gives information about the functioning of the cochlea and the start of the nerve pathway to the brain. Testing can give information about hearing at different frequencies. In children, this test is performed in hospital under anaesthetic. Auditory Steady-State Response (ASSR) This test is also known as Steady-State Evoked Potential, or SSEP. Auditory Steady-State Response results are recorded in the same way we measure ABR. That is, electrodes are placed on your child s head to record electrical energy that occurs in the auditory pathway in response to sound. This allows recording of the auditory system s response to specific frequencies and different intensities. ASSR is more accurate for severe-to-profound hearing losses than mild-tomoderate losses. Cortical Auditory Evoked Potentials (CAEP) Cortical Auditory Evoked Potentials (CAEP) are another measure that uses electrodes placed on your baby s head. An important difference is that CAEP measures electrical activity from the auditory area of the brain in response to sound. This test is particularly valuable because, as well as testing unaided hearing, it can also be used to test a baby s hearing when they are wearing their hearing aids. In this case, it is referred to as Aided Cortical Assessment (ACA). Your baby will need to sit or lie quietly, facing towards a loudspeaker which plays specially adapted speech sounds. For unaided testing, sounds can also be delivered via insert earphones or a bone conductor. Because the electrical signal picked up by the electrodes is very tiny, the signal must be measured many times to get a reliable result. For cortical potential tests, your baby needs to be awake but still and quiet to obtain results. The importance of a test battery The combination of tests used to test a child s hearing is often referred to as a test battery. The test battery will vary depending on the age of your child and the questions that need to be answered about your child s hearing.when assessing your child s hearing, the audiologist will select tests appropriate to your child s age and abilities, and their known risk factors for hearing loss. The ultimate goal is to obtain accurate behavioural results. If this is not possible because of 5 / 6
Powered by TCPDF (www.tcpdf.org) Australian Hearing age or abilities, a selection of objective tests is used to build a picture of how the auditory system is working in each ear. If your child is known to have a hearing loss, objective tests are also important to help identify the location of the hearing problem in the auditory system. If your baby was identified through newborn hearing screening, their hearing will be tested by state hospital audiologists following a specific test battery. However, hearing can change because of middle ear problems and because of the nature of some types of hearing loss. Also, hearing aid fitting often requires more detailed information than is provided by diagnostic tests used to refer babies to Australian Hearing. For these reasons, Australian Hearing audiologists will often need to repeat certain tests or perform further tests for your baby. Ongoing care Once your child s hearing has been evaluated and their hearing aids have been fitted and adjusted, your child will have their hearing regularly checked and their aids reviewed. Typically, a pre-schooler will attend two to four appointments with an audiologist each year. 6 / 6