Testing Newborn Babies

The otoacoustic emissions (OAE) test is a quick, simple and painless way to screen new-born's for hearing loss. A small earpiece containing a microphone and a mini-loudspeaker is placed in the ear. The loudspeaker makes clicking sounds in the ear. These are passed to the fluid-filled chamber called the cochlea. If the cochlea is working normally, it responds sending a sound back to the ear canal. This is detected by the microphone. The test is so sensitive that even a slight hearing loss can be detected and if there is a good response then no further checks are needed. Sometimes, the response cannot be detected when the test is done. This could point toward hearing problems but initially it is more likely to be due to other factors. This could be because the baby is unsettled, the room was noisy or there was some fluid left in the ear after birth. The test will usually be repeated and if there is still not a good response then it will be followed up with another type of test called an auditory brainstem response (ABR) test.

In an AABR test a small earphone plays clicks into the baby ear. If the baby can hear the click, a signal in the hearing nerve can be measured from sensors that are placed on the baby skin. The loudness of the clicks is set to a particular level. If this does not produce a response, further diagnostic testing will be required.

Both OAE and ABR testing are best done when the child is asleep, as the response to be detected is very small and can be hidden if there is a lot of movement.

Testing in Babies & Young Children

In young children a technique called visual reinforcement audiometry is used. In this test the child hears sounds, usually through speakers in the testing room. When the child hears the sound and turns their head towards it they are given a reward. Usually this is a visual reward such as the flashing lights of a toy. The person testing the child hearing continues reinforcing this behaviour with a reward every time the child turns towards a sound. Then the person carrying out the test begins to assess the child hearing by seeing if they respond to different types of sound. By doing this it is possible to find the quietest sound the child can hear.

Different variations of this reward-based test are used as a child gets older and finds it easier to communicate.