At your first visit to the audiologist or hearing aid practitioner you may undergo several hearing tests. These tests help determine whether you have hearing loss, as well as the type, pattern and degree of loss. You may also be tested on your ability to understand speech.
Audiometric tests determine a person’s hearing levels with the help of an instrument called an audiometer. The audiometer can also be used to measure your ability to discriminate between different sound intensities, recognize pitch or distinguish speech from background noise.
To complete the testing you will be asked to enter a sound booth. Once in the sound booth you will be told to push a button or raise your hand when you hear a sound. You will listen for various tones or beeping sounds that vary in pitch from bass, or low pitch, to treble, or high pitched sounds. The loudness or intensity of the sound is varied by the tester in order to determine how loud these various pitched sounds need to be before you can hear then. The results of this test provide a “pure tone audiogram” which illustrates which tones you do, or do not hear.
The result of a patient’s hearing screening are illustrated on a graph called an audiogram. Think of it as a picture of your hearing ability. An audiogram indicates how much hearing varies from normal and if there is a hearing loss, where the problem might be located in the hearing pathway. See below for an explanation of how to read an audiogram:
- Across the top of the graph there are numbers from 125 to 8000. These numbers (measured in HZ) represent the frequency (pitches) of the sound presented to the patient. They can be thought of as keys on a piano ranging from the base notes (125 Hz) to the treble notes (800 Hz). To get an idea of frequency, “middle C” on a piano registers at 250 Hz. Each vertical line on the audiogram represents an increase in frequency of about an octave on the piano. A dog barks at about 250 Hz and the birds sing at about 6000 Hz.
- On the left side of the graph there are numbers from 0 to 120. These numbers represent the intensity (loudness) of sounds and are measured in decibels (dB). Zero decibels (0dB) does not mean ‘no sound”, it is just extremely soft. Conversational voice level is around 65dB, and 120dB is very loud – about as loud as a jet taking off if you are standing 100 metres away.
- It should be noted that in this scale of measurement 20 dB is not twice as loud as 10 dB. Rather it is 10 times as loud, just as 30 dB is 10 times as loud as 20 dB and so on. The increase is logarithmic, like a spiral. This explains why hearing loss is not measured as a percentage of loss.
- The alphabetical letters on this audiogram represent the loudness and frequency of the sounds that make up the human voice, spoken at conversational levels.
- The shaded area is called the “speech banana” because that is the area of the audiogram where normal speech is heard.
To help you understand your hearing loss, you can get a copy of your audiogram (it belongs to you) and plot the points as you reread the above information.
Speech Discrimination Testing
A speech discrimination test assesses how well you understand words. For this test you are asked to listen to words through headphones at a volume loud enough to overcome your hearing loss. The test uses word with vowels and consonants that are distributed similarly to those words used in ordinary conversations – words such as jar, this, box, and car. The audiologist asks you to repeat the words you hear.
This test helps determine whether you have distortion as a result of a nerve, or sensorineural hearing loss. Although it doesn’t mean your hearing is good, a high score on the speech discrimination test is good news. It means that you stand to benefit the most from a hearing aid, because boosting the volume of words may help you understand them better. If you understand only a low percentage of words, this explains why simply turning up the volume with a hearing aid is unlikely to help you hear any more clearly.