By Dr. Danko Cerenko, M.D., Ph.D.

When we talk about hearing function, people associate it with the function of the ear. But the ear is only the first part of the complex hearing (auditory) system that consists of three units:

1. The ear (external, middle and inner ear) serves to gather the sound waves and convert them into the electrical impulses

2. Hearing (auditory) nerve which carries the electrical impulses generated by the hair cells in the inner ear to the third unit

3. The hearing center (auditory cortex) in the brain where the recognition of sounds and speech actually occurs.

An audiologist (hearing professional) will perform a battery of diagnostic tests to assess all three units of the hearing system. In a soundproof booth the softest volume sounds can be heard is determined at a variety of frequencies or pitches in each ear. Each tone is standardized and defined by its frequency: 250, 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hertz (Hz) and corresponds with sounds frequently heard in speech or the environment. These tones are presented by air conduction through speakers or headphones and also by bone conduction through an oscillator placed on the mastoid bone behind the ear.
The result of the above air and bone conduction tests are presented in a graph called an audiogram. The red line connecting the "Os" indicates the softest ability to hear at each frequency for the right ear by air conduction. The blue line connecting the "Xs" indicates the same for the left ear. The signs for the bone conduction are [ for the right ear, and ] for the left ear. While testing the latter, presented sound waves by-pass the middle ear and stimulate the inner ear directly. Examples of common audiograms are included at the end of this article.

The audiologist will also determine the softest volume the patient can repeat very simple two-syllable words to establish the speech recognition threshold. Then, the audiologist will present an additional series of words at a comfortable listening level to determine the percentage of words repeated correctly. This speech discrimination score is also a predictive factor of success when counseling the patient for hearing aids.

The hearing professional may also administer additional tests to further pinpoint the possible problem area in the hearing system. Tympanograms, acoustic reflex thresholds, acoustic reflex decay, and otoacoustic emmissions tests are some such tests. Audiologists are also trained to use special testing methods with young children or patients with disabilities which make traditional testing methods ineffective.

A thorough review of all hearing system test results helps physicians to determine the overall efficacy of the entire hearing system. Based on the tests results, physicians will take other steps to try to determine the cause of the hearing abnormality. Treatment options for diseases and disorders of the hearing system may include: observation, additional testing, medical or surgical management of the condition that is causing the hearing loss, and the recommendation for hearing aids.