A basic hearing test or pure tone audiometry is a test to find out the softest levels of sound a person can hear at individual pitches of sounds (hearing thresholds). When a sound is heard, the person responds by pressing a button or raising a hand.
For young children, responding to the sound by pressing a button or raising a hand in a hearing test is not too interesting and they get bored easily. In order to motivate them, they respond to sounds whilst engaged in play activities such as putting a peg in a pegboard or placing a car on a runway.
For babies and toddlers who are not old enough to engage in structured play activities, they will be conditioned to turn to a source of sound. The headturn will be reinforced by a reward such as a blinking toy, a puppet or a cartoon video.
SSEP (Steady State Evoked Potentials) is used when a person such as an infant who could not cooperate in a hearing test. Electrodes will be applied on the skin surface of the head when the patient is sleeping to record the hearing nerve activity in response to sounds being delivered into the ears. The hearing thresholds could be estimated by this test. ABR (Auditory Brainstem Response) test is similar to the SSEP but it usually only estimates hearing thresholds to the high pitched sounds. ABR is also very usefully in diagnosing pathology in the hearing nerve.
SSEP and ABR can be used in conjunction for a more accurate diagnosis. However, the best test is still one in which the patient can cooperate and respond to sounds reliably in the hearing booth.
EcochG or Electrocochleagraphy is also a test of the hearing nerve in response to sound but the test zooms in on a different area. It is commonly used to test for changes in volume of fluids in the inner ear in certain diseases such as the Meniere's Disease.
Tympanometry is a test of the middle ear. It is able to test if the eardrum is ruptured or if there is an ear infection, common in children.
OAE stands for Otoacoustic Emissions. It is a test of the inner ear function and forms the basis of the tests commonly used in newborn hearing screening.
As the human ear is also linked to the balance organ, we also conduct a test set to detect anormalies in the balance organs, generally known as vestibular testing. The tests in the set capitalise on the relationship between eye movements and the balance organs. Changes in eye movement recordings form the basis of these tests.
About 1 in 1000 babies in Singapore have significant hearing impairment at birth and are at risk for delay in speech, language, intellectual, social and emotional development. Early detection followed by appropriate intervention will minimise the harmful effects on the child’s development. Without a screening test, this impairment may not be detected until much later. Thus, the aim of the screening test is to detect hearing loss early, in order to facilitate intervention and treatment as quickly as possible (preferably by 6 months of age).
The screening test is performed within the first few days after birth, and usually prior to the discharge of your baby. It is performed by trained staff and takes about 15 to 30 minutes. The screening test is safe and will not hurt your baby in any way.
Depending on the hospital, the machine used to test your baby’s hearing may be an Otoacoustic Emission (OAE) instrument or an Automated Auditory Brainstem Response (AABR®) instrument.
For the OAE, a small ear probe is placed at the opening of your baby’s ears. The instrument makes clicking sounds and the probe listens to the responses (echoes) from the baby’s ears.
For the AABR®, three Jelly TabTM sensors are applied to the head. A soft earphone delivering clicking sounds will evoke responses from your baby which will be recorded by the instrument. The staff will inform you of the result after the test.
This means that your baby’s hearing function is normal at the time of testing. However, in some babies, hearing impairment may develop gradually as a result of recurrent ear infections, genetic factors, or chronic illnesses. Hence, you need to be vigilant and continue to monitor the behavioural responses of your child’s hearing ability according to the checklist provided in the Baby Health Booklet. If you suspect at any time that your child has a hearing problem, you should consult your doctor.
It does not necessarily mean that your baby has a hearing impairment, but further investigation will be needed. If your baby does not pass the repeat screening test, a referral will be made to the ENT (Ear, Nose, Throat) specialists,who may decide on further confirmatory test. It is very important to attend these appointments so that any hearing impairment can be diagnosed early and precious time is not lost to help your child develop normally.