What is an Audiogram ?
A pure tone audiogram is a graph which indicates how well one hears a range of sounds.
What does it tell you ?
An audiogram indicates the softest levels of sounds that a person can hear. It is used to determine whether a person is hearing within normal limits, or whether a person has a hearing loss. It also indicates the nature of the hearing loss.
How is an audiogram obtained ?
Using an audiometer, the tester will produce different pitches at varying levels of loudness. The person being tested is instructed to raise his hand or press a button whenever he hears a sound, even when the sound is very soft.
For testing young children, the child will be conditioned to put a peg in a pegboard or perform a similar task whenever they hear the sound.
For those who are too young to use the pegboard or raise their hand, soundfield testing is done. This involves either observing the child's behavioural response to sounds, or having the child look to a visual reinforcer after each sound is presented.
For much more detailed information, see the assessment page.
How is the loudness of the sounds measured ?
(a link somewhere to CHS bookmark info)
In decibels (dB). The decibel is the unit of measurement for loudness. On the audiogram, the range of decibels is displayed along the vertical axis and extends from -10 dB to 120 dB.
-10 dB represents extremely soft levels, whereas 120 dB represents extremely loud levels.
How are the different pitches measured ?
Hertz (Hz) are the unit of measurement for pitch. On the audiogram, the range of pitches is displayed along the horizontal axis and extends from 125 Hz to 8000 Hz. Like a piano, the pitches start off low (125 Hz) and end up in the high range (8000 Hz). The pitches used in hearing testing are most often 250, 500, 1000, 2000, 4000 and 8000 Hz. These are the pitches most important for speech.
What are the speech frequencies ?
Low-pitched sounds (ex., 250 & 500 Hz) include most of the vowel sounds as well as consonants such as "m", "n", "b", and "g".
High-pitched sounds ( 2000 - 6000 Hz) include many consonant sounds such as "s", "t", "f" and "sh".
The other consonant sounds are found throughout the mid-frequency range.
What do the symbols on the audiogram mean ?
There are two kinds of testing: air conduction and bone conduction.
Air conduction testing for the right ear is marked O and D; the left ear is marked X and ÿ
Bone conduction testing for the right ear is marked [ and < ; the left ear is marked ] and > When no response is obtained, this is marked ¯ When soundfield is used to test, the responses for the better ear are marked S and W
What does air conduction mean ?
Air conduction is the passage of sound by air (through the headphone, insert phone or speaker) to the ear drum and subsequently to the ossicles (tiny bones in the middle ear) and the cochlea (inner ear). This leads to stimulation of the nerve cells of the inner ear.
What does bone conduction mean?
Bone conduction is the passage of sound through the bones of the skull to the inner ear. This is done through the placement of a bone vibrator behind the ear, which sends the sound directly to the inner ear through the vibration of the skull. As opposed to air conduction, this bypasses the outer and middle ear.
What do air and bone conduction testing tell us ?
These tell us whether the hearing loss is conductive, sensorineural, or mixed. This is because these tests determine where the problem is within the ear.
If the problem lies in the outer or middle ear, the results of air conduction testing will show up as abnormal but at the same time hearing through bone conduction testing will reveal normal hearing sensitivity. This type of problem can usually be cleared up medically or surgically, and may therefore be temporary. Common causes of conductive losses are:ear infections, holes in the eardrum, wax build-up, problems with the bones in the middle ear, atresia and stenosis. (glossary)
If the problem lies in the inner ear, the results of both air and bone conduction testing will show up as abnormal. This type of hearing loss cannot be treated medically or with surgery, and is therefore permanent in nature. If they wish, people with this kind of hearing loss may benefit from a hearing aid or cochlear implant.
What is speech audiometry ?
Speech audiometry is the use of audiological tests that use spoken words and sentences rather than pure tones.
What is the Speech Reception Threshold (SRT) ?
This is the softest level at which a person can understand familiar two word syllable words. These words are called spondees which refer to the equal stress that is put on both syllables (for example, cupcake, toothbrush, popcorn)
What is the SRT used for ?
The SRT is first used to test the reliability of the pure tone audiogram. The SRT should be about the same threshold as the pure tones at 500, 1000 and 2000 Hz. Secondly, the SRT is used to measure the minimum level of loudness that is necessary for the understanding of simple words. Thirdly, the SRT provides a baseline for other speech tests.
What is the Speech Awareness Threshold (SAT) ?
This is the softest level that a person can detect the presence of speech.
What is the SAT used for ?
The SAT provides a measure of the minimum loudness level necessary to hear speech (i.e., to be aware that someone is talking).
What is speech discrimination ?
Speech discrimination (discrim.) is the use of phonetically balanced, single syllable words. These words are balanced in such a way that they represent all of the sounds of English.
What is it used for ?
It is used in order to assess a person's ability to identify and repeat words presented at a suprathreshold level.
How are Speech Discrimination Scores obtained ?
Lists of 25-50 words are presented to the patient at a loudness level of about 30 dB louder than their SRT score, which ensures that the patient is hearing the words sufficiently. The number of words that the patient repeats correctly is converted to a percentage score out of 100.
The Meaning of Speech Discrimination Scores
90-100% words correctly repeated
Excellent word discrimination
75-89% words correctly repeated
Slight difficulty in discrimination
60-74% words correctly repeated
Moderate discrimination difficulty
50-60% words correctly repeated
Poor word discrimination
Under 50% of words correctly repeated
Very poor word discrimination