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Diagnostic Hearing Tests

The inner ear is made of two parts – the cochlear, which is involved in hearing, and the vestibular system which is involved in balance. Once sounds are heard by the inner ear the information is transmitted along the hearing nerve by complex pathways up to the brain.

There are tests which are used to assess different parts of the hearing pathway and balance system or to test for particular medical conditions which can affect the hearing system. Some of these tests are:-

Otoacoutic emissions: This test assesses a part of the inner ear called the outer hair cells. A soft plug is placed into the ear canal to measure for the acoustic signals generated by the outer hair cells. Most often emissions occur in response to sound and during the test sounds will be played into the ear through the plug. There are no side effects to this test.

Auditory brainstem responses: This test is used to assess the function of the hearing nerve which travels from the inner ear up to the brain. Electrodes placed on the surface of the skin are used to record very small electrical signals that are created as the information is sent along the hearing nerve. The electrodes are placed behind the ears, on the forehead and the neck. During the test clicking sounds are heard in the ear. The test is carried out while you are lying down on a bed and usually takes between 30 to 60 minutes. There are no side effects to this test.

Electrocochleography: This test may be used to assess for imbalance in the fluid pressure of the chambers of the inner ear or for evidence of a ‘fistula’ or hole between the fluid chambers of the inner ear. Recordings are made of the electrical activity of the inner ear in response to sound. During the recording a very small electrode is guided along the ear canal to gently rest against the ear drum. Loud clicks are then delivered into the ear to record its response. In a small number of cases people may feel dizzy following this test so it is recommended that you have someone accompany you to the clinic. This test may take up to one hour.

Cortical Evoked Auditory Responses: This test assesses the electrical activity that occurs when the auditory area of the brain processes sound information. This activity is recorded by electrodes placed on the surface of the head. Sounds are delivered into the ear by an earphone. There are several variations of this test; some require you to focus very closely on the sounds while others do not. This test is usually carried out while you are lying down on a bed. The test usually takes between 30 to 60 minutes. There are no side effects to this test.