It is never too early to test a child's hearing. The type of procedure used to test hearing will depend on the age of the child.
Common Types of Testing
Soundfield (Behavioral) Testing
During soundfield testing, the child sits on the parent's lap. Sounds are presented via loudspeakers. The audiologist watches the child as they respond to the sounds. In very young children, the audiologist will look for responses such as an eyeblink or slight body movement. Older children are trained to turn toward the sound. When turning toward the sound, the child will see a lighted toy as a reward.
Testing Under Headphones
Headphone testing provides the audiologist with information regarding the child's ability to hear with each ear. Testing begins by finding the softest level at which the child is able to repeat words or point to pictures. The child is asked to respond to sounds of various pitches by raising their hand or by performing an act, such as dropping a block into a container. This test, an audiogram, evaluates the child's ability to hear certain sound frequencies.
Bone Conduction Testing
Bone conduction testing evaluates the function of the inner ear or nerve portion of the ear. A small vibrator is placed behind the child's ear and they are asked to repeat or identify words, or respond to sounds of different frequencies. The results are compared to results obtained under headphones or through loudspeakers to help the audiologist identify the type of hearing loss.
Otoacoustic emission testing assesses the function of the inner ear, specifically the outer hair cells. A small probe is placed in the child's ear. Sounds are presented to the ear and an emission ("echo") from the ear is measured. The result helps to determine if a child has normal hearing.
Immittance testing, often referred to as a tympanometry, provides information regarding eardrum mobility and middle ear function. A small plastic tip is placed in the child's ear to make an airtight seal. Changes in air pressure are made and measures are taken. If the child has ear tubes, this test helps determine if the tubes are in place, open and working properly. If the child does not have tubes, this test helps determine if there are any signs of fluid or other problems in the middle ear. Reflex action of the ear is also measured with immittance testing.
Auditory Brainstem Response (ABR) Testing
The ABR provides information regarding the softest level of sound that a person can hear. During the test, several electrodes are taped onto the child's head and a small earphone is placed into each ear. These electrodes are used to monitor brainwave activity as the child listens to sounds at different levels of loudness. The brainwave patterns of the ABR are evaluated to determine the softest level of sound each ear can hear. If there is a hearing loss, the ABR helps to determine the type and severity of the problem.
Who Should Have an ABR?
The ABR is most commonly recommended for infants or very young children. It can also be used to evaluate older children who will not cooperate during other types of hearing tests. The ABR is usually not necessary in healthy children over 3 years of age, if the child will wear headphones and cooperate during a behavioral hearing test. The ABR is often performed as part of a complete test battery, which includes behavioral testing, and tympanometry and otoacoustic emissions. It is important that a series of tests be performed to accurately determine the presence, degree and type of hearing loss.