11 January 2012

A hearing test does not always detect hearing loss

Some hearing loss can be difficult to detect with traditional methods. A more detailed hearing test can however identify problems; a research project has now shown.

Some people have hearing problems which an ordinary hearing test cannot uncover. A Danish research project has used a method which can precisely identify where the problem lies.

Hearing problems which cannot be detected by ordinary methods are called by some Obscure auditory dysfunctions. An ordinary hearing test examines how we hear sounds at 250, 500, 1000, 2000 and 4000Hz (Hz is a unit of sound vibration). A traditional hearing test does not examine how we experience the sounds which lie between these tones.

Researcher Christian Brandt of University of South Denmark has studied 14 patients with special hearing problems. He has examined their hearing by taking hearing tests with very small tone adjustments, which are comparable to the change in tones on a piano.

“With the study, I documented that they had hearing problems,” says Christian Brandt, M. Sc and Ph. D to the magazine Hørelsen, which is the magazine for members of the Danish union of hearing impaired people.

Where is the problem?

With the study, he could localise the problem. 11 of the participants had damage to their cochlea in the inner ear, while three had problems in the brain's processing of the signals from the inner ear.

“If the ear does not send the right signals to the brain, the brain does not have a chance of understanding what is going on. But if the brain gets the right signals from the inner ear, but does not process them correctly, there will also be problems with your hearing,” says Christian Brandt to Hørelsen.

Two kinds of hair cell

Some hearing damage is the result of damage to the Cochlea in the inner ear. In the Cochlea are a mass of small hair cells which capture sound and send them on to the brain. Christian Brandt says that there are two types of hair cell in the Cochlea: The outer cells which amplify the signals and the inner hair cells which produce the electrical signals which are sent to the brain.

If the outer hair cells are damaged, you can still hear, but the sound will be weak because the amplification is missing. When the damage is in the inner hair cells, you cannot hear anything, because the electrical signals are not being sent to the brain, says Christian Brandt.

Source: Hørelsen, January 2010.