How and when a child should be tested depends on a number of factors including genetic predisposition for hearing impairment and whether the child has been exposed to certain risk factors.
Some of the hearing tests may be used for children of all ages, while others are used based on the child's age and level of understanding.
Testing the newborn
Hearing screening of newborns before they leave the hospital or maternity ward is becoming a common practise. It is important that the child's hearing loss is diagnosed before 3 months of age. A baby with a hearing loss present at birth should start treatment before the age of 6 months, which is an important time for speech and language development. Children whose hearing loss is identified early and who receive early intervention are found to function at the level of their peers by the time they enter school.
There are two primary screening tests for newborns. Both tests are painless, take only a few minutes, and are best done while the baby is sleeping.
- An Otoacoustic Emission test (OAE), in which a tiny microphone is placed in the baby's ear. Sounds are transmitted into the ear, and the sounds that are emitted by the cochlea are recorded in the ear canal. Thresholds at certain frequencies can be determined by analysing the emissions. If the baby has a hearing loss there will be no emission of sound.
- An Auditory Brainstem Response (ABR) test, which uses electrodes placed at several locations on the baby's head and ear. While the baby is resting an acoustic stimulus is presented to each ear either through headphones or insert-earphones. An analysis of the activity in the brain reveals the thresholds of hearing.
A baby that does not pass the screening tests should be re-screened to confirm results and receive an in-depth evaluation by an audiologist.
Testing the infant (7 months to 2 years of age)
In addition to the above mentioned tests, a hearing test of the infant may include:
- A simple behavioural audiometry test that includes the use of hand-held sound stimuli representing various frequency ranges (for example a drum, rattle, bell, etc.). This test is used to observe the infant's behaviour in response to certain sounds.
- Sound field testing with visual reinforcement during which the infant is exposed to a variety of sounds through loudspeakers. The infant is trained to turn towards any sound source. When responding, the child is “rewarded” through an entertaining visual image or toy.
If the infant does not pass these tests a referral for an evaluation by an audiologist is needed.
Testing the toddler (2 to 3 years old)
When evaluating the hearing of a toddler the following test may also be used:
- Conditioned play audiometry (CPA) is a headphone testing used on infants and young children mature enough to tolerate this test strategy, which provides specific information about the hearing loss. The test is often made into a game and the child is asked to do something with a toy (e.g. touch a toy) every time a sound is heard. The test thus relies on the active participation of the toddler.
If the toddler does not pass the hearing test an in-depth evaluation by an audiologist is recommended.
Testing the older child
- Tympanometry is a test that may help determine how the child's inner ear is functioning. Air pressure is transmitted into the ear making the ear drum move. The mobility of the eardrum is then measured by a special machine. The test does not determine if the child is hearing or not but can detect changes in the pressure of the inner ear. This test requires the child to sit very still and is mostly used on older children.