In some cases, for very young infants and difficult to test children, behavioral tests cannot be done nor can they provide all of the information needed to project an accurate diagnosis of hearing loss. As a result, objective tests such as the physiological and electrophysiological tests can be used to determine what part of the auditory system is dysfunctional and/or to predict hearing status in patients who are not able to complete standard hearing tests. 

This form of testing involves the use of electrical recording to investigate physiological function or dysfunction within the body such as the auditory evoked potential measurements.

Auditory Evoked Potential Measurements (AEP)

By means of computer averaging, it is possible to extract and record (via electrodes placed on the scalp) the very small electrical voltage potentials evoked in the brain by acoustic stimulation. These electrical events are complex and can be observed over a broad time interval after the onset of stimulation. An AEP is a wave form that reflects the electrophysiologic function of a certain portion of the central auditory nervous system in response to sound, thus, they are used for several purposes in evaluating the auditory system. Because early evoked potentials can be recorded even with unconscious patients, they have become an invaluable part of pediatric assessment.

AEP measurements varies, however, the most common measurement is a test known as the Auditory Brainstem Response (ABR) test. This test has several applications and is used in the assessment of hearing function in infants, children and adults.

Screening ABR

For infants, the ABR test is often used to screen for hearing loss in the newborn period. The infant sleeps while sounds are played to the ear through a small earphone. Recording electrodes on the head sends the response to a computer. The test can be conducted during the first 24 to 48 hours of life.

Threshold Estimation ABR Evaluation

This procedure provides an objective test in order to predict hearing sensitivity for a range of test frequencies, usually (500Hz-4000Hz). The test technique is similar to the ABR screening test except that the child must remain quiet for one hour or longer, so a mild sedative may be used for children over 4 months of age. This test can provide information in order to predict the type, degree, and configuration of hearing loss.  

Diagnostic ABR

ABR is a sensitive indicator of functional disorders of the acoustic nerve and lower auditory brainstem. Therefore, it can be used as a screening tool to assess the presence of retro cochlear pathology (tumors) and other abnormalities that alter the function of this area.

Electrocochleography (ECoG)

This specialized test is used to assess inner-ear function and can be used for patients with dizziness problems and/or those with suspected hearing nerve dysfunction such as auditory neuropathy. The procedure is similar to the ABR test, except that electrodes are placed in the ear canals as well as on the head. As with the ABR, sounds are played to the ear as responses are recorded. Results can provide information regarding a possible imbalance of fluids in the inner ear.

Otoacoustic Emissions (OAE) Test

An Otoacoustic emission (OAE) testing is the recording of sounds that the ear itself produces. Generally speaking there are two types of OAE, Spontaneous Otoacoustic Emissions (SOAEs), which can occur without external stimulation, and Evoked Otoacoustic Emissions (EOAEs), which require an evoking stimulus. The OAE test can be used to determine if the outer hair cells in the inner ear are functioning normally. The procedure is painless and can be performed even within the first day or two of life.

To measure OAEs, a miniature earphone and microphone are placed in the ear canal. Sounds are presented and a response from the inner ear is recorded. Patients do not need to respond in any way; they simply need to remain still for approximately 1 to 2 minutes.