Parents and caregivers often ask how hearing can be tested in infants and young children. The truth is, no child is “too young to test.” Audiologists are trained to evaluate even the youngest patients through a combination of tools and techniques designed to provide information on the auditory system starting from birth.
Otoacoustic emissions are tested by placing a small probe in the ear that emits a soft sound. A normally functioning cochlea will send back an inaudible echo, or otoacoustic emission, through the middle ear that can be measured by this probe. When otoacoustic emissions are present, they indicate a functional cochlea.
Auditory brainstem response (ABR) testing is completed to determine whether the cochlear and auditory nerve are functioning. Electrodes are placed on the head and ears to record the electrical activity within the ears. Sound is presented through earphones and a computer is used to read the response from the cochlea and auditory nerve. By observing the response to sounds, it is possible to determine whether hearing is normal or impaired and to estimate the degree, type and configuration of hearing loss. In order to complete this test, the infant or child must be sleeping. For very young infants, the test is completed in natural sleep. For older infants or young children, sedation is used.
By about 6 months of age, most children are able to localize sound in their environments. In visual reinforcement audiometry, the audiologist reinforces this natural tendency by using a lighted toy to capture the child’s attention when she turns toward the sound. Using this method, it is possible to test children’s hearing from about six months through about age two years. Tones or speech may be used during this test.
From about age two to four years old, children can be engaged in a game to test hearing. During conditioned play audiometry, the child is trained to respond to the sound by participating in an activity such as placing a block in a bucket, putting pegs in a board, etc. Sounds are tested at different frequencies and intensities to determine the lowest level at which a child can hear a given tone. At this age, the child’s speech perception may also be tested by having her point to a picture or repeat words.
Additional testing may include evaluation of the middle ear system. Tympanometry is used to measure the mobility of the tympanic membrane, or eardrum. A probe is placed in the ear and a slight pressure is presented; the movement of the eardrum is recorded on a computer screen.
Acoustic reflexes are measured using a probe in the ear as well. A loud sound is briefly presented; in response, the stapedius muscle contracts. This is used to evaluate the middle ear and the low brainstem portion of the auditory pathway.