Audiometry includes tests of mechanical sound transmission (middle ear function), neural sound transmission (cochlear function), and speech discrimination ability (central integration). A complete evaluation of a patient's hearing must be done by trained personnel using instruments designed specifically for this purpose. The audiogram reads in frequency (pitch) across the top or horizontal axis and it reads in decibels (loudness) down the side or vertical axis. Just like a piano's keyboard.
The loudness scale goes from very soft sounds at the top (-10 or 0dB) to very loud sounds at the bottom (110 dB). It is important to remember that 0 dB does not mean that there is no sound at all. It is simply the softest sound that a person with normal hearing ability would be able to detect at least 50% of the time. Normal conversational speech is about 45 dB.
Techniques:
1. Pure tone audiometric air conduction testing
presenting a pure tone to the ear through an earphone and measuring the lowest intensity in decibels (dB) at which this tone is perceived 50% of the time. This measurement is called threshold. The testing procedure is repeated at specific frequencies from 250 to 8000 hertz (Hz, or cycles per second) for each ear, and the thresholds are recorded on a graph called an audiogram.
2. Bone-conduction testing
Done by gently resting bone-conductor on the mastoid process of the skull (the bone behind the ear) and is held in place by a small metal band stretching over the top of the head
3. Impedance audiometry
A hermetic seal is obtained by inserting a probe tip in the external ear canal. The pressure in the enclosed cavity is varied from + 200 to − 200 mm H2O and the change in sound pressure level of a probe tone is graphed
4. Auditory brainstem response (ABR) audiometry
Electrodes are placed on the patient's vertex, earlobes, and forehead. Clicks are delivered through earphones, and a computer sums the time-locked responses (potentials) for the first 10 msec after sound stimulation.
*Pure tone test - 1 & 2. Masking noise is sometimes used in the nontest ear to prevent its participation in the test
Hearing thresholds within normal ranges for the left ear
White area represents the sounds that the person would not hear (softer then their thresholds) and the tan area indicates all of the sounds that the person would be able to hear (louder then their thresholds).
Thresholds from zero to 15 dB are considered to be within the normal hearing range. After that point, people will usually begin to display some communication difficulties because of the elevated hearing thresholds. The 100 dB point should not be confused with a 100% hearing loss, which is a total lack of hearing.
Sensorineural hearing loss is also referred to as "nerve deafness:"
This type of hearing loss is frequently not medically or surgically treatable. It is typically permanent and irreversible. However, most people with sensorineural loss find wearing hearing aids to be of significant benefit and some people with severe loss can benefit from a cochlear implant.
*Hey guys, i'm not gonna post up the explanation for this graph here. It's gonna be really wordy. so...... for more info, refer to
http://www.hearingresearch.org/Dr.Ross/Audiogram/Audiogram.htm
There are extra information there too. Pretty interesting =D
DO check it out!
References:
http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=cm&part=A3897
http://www.hearingresearch.org/Dr.Ross/Audiogram/Audiogram.htm
http://www.audiologyawareness.com/hearinfo_audiogramread.asp
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