Audiometry
Encyclopedia
Audiometry is the testing of hearing ability, involving thresholds and differing frequencies. Typically, audiometric tests determine a subject's hearing levels
with the help of an audiometer
, but may also measure ability to discriminate between different sound intensities, recognize pitch
, or distinguished speech
from background noise. Acoustic reflex
and otoacoustic emission
s may also be measured. Results of audiometric tests are used to diagnose hearing loss or diseases of the ear
, and often make use of an Audiogram
.
The most commonly used assessment of hearing is the determination of the threshold of audibility, i.e. the level of sound required to be just audible. This level can vary
for an individual over a range of up to 5 dB from day to day and from determination to determination, but it provides an additional and useful tool in monitoring the potential ill
effects of exposure to noise. Before carrying out a hearing test, it is important to obtain information about the person’s past medical history, not only concerning the ears but also other conditions which may have a bearing on possible hearing loss detected by an audiometric test. The hearing loss is usually bilateral, but variations in each ear have been observed. Wax in the ear can also cause hearing loss, so the ear should be examined to see if syringing is needed; also to determine if the eardrum has suffered any damage which may reduce the ability of sound to be transported to the cochlea.
Firstly, a threshold test is undertaken in which each ear is subjected to sound at a frequency of 1 kHz at varying levels of intensity ranging from low to high and high to low. The procedure is repeated several times so that an average threshold can be derived for the test. Thresholds can vary due to slight changes in the procedures adopted in
setting up the test, e.g. variation of the position of the earphone on the ear.
Following this pre-check, both of the subject’s ears are tested through a range of frequencies (usually 0.5, 1, 2, 3, 4 6 and 8 kHz) and hearing loss recorded for each frequency, again via a series of sound exposures. From them an average result can be computed.
The accuracy of audiometry can be affected by four main factors:
A further complication of audiometric testing is that it is subjective and relies on the cooperation of the subject. If the subject is unable or unwilling to co-operate with the test then unrepresentative results will be obtained.
The technique described above enables a comparison the threshold of hearing of the individual undergoing audiometry with a reference value at a range of octave band frequencies (125, 250, 500, 1000, 2000, 4000, 8000 Hz). From this data a pictorial representation, an audiogram, of hearing loss at various frequencies is produced.
Equal-loudness contour
An equal-loudness contour is a measure of sound pressure , over the frequency spectrum, for which a listener perceives a constant loudness when presented with pure steady tones. The unit of measurement for loudness levels is the phon, and is arrived at by reference to equal-loudness contours...
with the help of an audiometer
Audiometer
An audiometer is a machine used for evaluating hearing loss. Audiometers are standard equipment at ENT clinics and in audiology centers. They usually consist of an embedded hardware unit connected to a pair of headphones and a test subject feedback button, sometimes controlled by a standard PC...
, but may also measure ability to discriminate between different sound intensities, recognize pitch
Pitch (music)
Pitch is an auditory perceptual property that allows the ordering of sounds on a frequency-related scale.Pitches are compared as "higher" and "lower" in the sense associated with musical melodies,...
, or distinguished speech
Interpersonal communication
Interpersonal communication is usually defined by communication scholars in numerous ways, usually describing participants who are dependent upon one another. It...
from background noise. Acoustic reflex
Acoustic reflex
The acoustic reflex is an involuntary muscle contraction that occurs in the middle ear of mammals in response to high-intensity sound stimuli....
and otoacoustic emission
Otoacoustic emission
An otoacoustic emission is a sound which is generated from within the inner ear. Having been predicted by Thomas Gold in 1948, its existence was first demonstrated experimentally by David Kemp in 1978 and otoacoustic emissions have since been shown to arise by a number of different cellular...
s may also be measured. Results of audiometric tests are used to diagnose hearing loss or diseases of the ear
Ear
The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....
, and often make use of an Audiogram
Audiogram
An audiogram is a standard way of representing a person's hearing loss . Most audiograms cover the limited range 100 Hz to 8000 Hz which is most important for clear understanding of speech, and they plot the threshold of hearing relative to a standardised curve that represents 'normal'...
.
The most commonly used assessment of hearing is the determination of the threshold of audibility, i.e. the level of sound required to be just audible. This level can vary
for an individual over a range of up to 5 dB from day to day and from determination to determination, but it provides an additional and useful tool in monitoring the potential ill
effects of exposure to noise. Before carrying out a hearing test, it is important to obtain information about the person’s past medical history, not only concerning the ears but also other conditions which may have a bearing on possible hearing loss detected by an audiometric test. The hearing loss is usually bilateral, but variations in each ear have been observed. Wax in the ear can also cause hearing loss, so the ear should be examined to see if syringing is needed; also to determine if the eardrum has suffered any damage which may reduce the ability of sound to be transported to the cochlea.
Types of Audiometry
- Subjective Audiometry
- 1. Pure tone audiometryPure tone audiometryPure tone audiometry is the key hearing test used to identify hearing threshold levels of an individual, enabling determination of the degree, type and configuration of a hearing loss. Thus, providing the basis for diagnosis and management. PTA is a subjective, behavioural measurement of hearing...
- 2. Speech audiometry
- 3. Bekesy audiometry
- 1. Pure tone audiometry
- Objective Audiometry
- 4. Acoustic impedance audiometry/ TympanometryTympanometryTympanometry is an examination used to test the condition of the middle ear and mobility of the eardrum and the conduction bones by creating variations of air pressure in the ear canal....
- 5. Evoked response audiometry
- 4. Acoustic impedance audiometry/ Tympanometry
Process
The audiometric test can be carried out using automatic or manual audiometers, but the essential test procedure is the same:- The subject is asked to remove anything which might upset the test results, e.g. spectacles, earrings, hearing aids.
- Instructions are given about the test procedure and the subject is required to indicate whether he/she can just hear or cannot hear a certain sound (the sound level may be increased from a very low level or reduced from a high level).
- Headphones are fitted carefully over the ears and the test is then carried out on each ear.
Firstly, a threshold test is undertaken in which each ear is subjected to sound at a frequency of 1 kHz at varying levels of intensity ranging from low to high and high to low. The procedure is repeated several times so that an average threshold can be derived for the test. Thresholds can vary due to slight changes in the procedures adopted in
setting up the test, e.g. variation of the position of the earphone on the ear.
Following this pre-check, both of the subject’s ears are tested through a range of frequencies (usually 0.5, 1, 2, 3, 4 6 and 8 kHz) and hearing loss recorded for each frequency, again via a series of sound exposures. From them an average result can be computed.
Errors and accuracy
When the test is completed, a second threshold check should be carried out to see that no errors have crept in during the test. Both threshold checks should agree within a maximum of 10 dB. If they do not, a re-test must be performed.The accuracy of audiometry can be affected by four main factors:
- Technical limitations – how accurately can either the frequency or the hearing level be determined?
- Learning effect – the first ear tested sometimes appears worse than the second one since the individual becomes more proficient at detecting the threshold.
- Headphone fit – some of the variation in threshold measurement has been attributed to differences in the location of the headphones, which in turn affect the detection of the threshold.
- Background noise – audiometric tests should be carried out in a sound-proof chamber to eliminate external sounds from influencing the test.
A further complication of audiometric testing is that it is subjective and relies on the cooperation of the subject. If the subject is unable or unwilling to co-operate with the test then unrepresentative results will be obtained.
The technique described above enables a comparison the threshold of hearing of the individual undergoing audiometry with a reference value at a range of octave band frequencies (125, 250, 500, 1000, 2000, 4000, 8000 Hz). From this data a pictorial representation, an audiogram, of hearing loss at various frequencies is produced.
See also
- AudiometerAudiometerAn audiometer is a machine used for evaluating hearing loss. Audiometers are standard equipment at ENT clinics and in audiology centers. They usually consist of an embedded hardware unit connected to a pair of headphones and a test subject feedback button, sometimes controlled by a standard PC...
- Equal-loudness contours
- AudiographyAudiographyAudiography in the context of filmmaking is a term commonly used in India to mean the audio engineering performed by the sound department of a film or TV production; this includes sound recording, editing, mixing and sound design but excludes musical composition, songwriting and choreography.An...
- Otoacoustic emissionOtoacoustic emissionAn otoacoustic emission is a sound which is generated from within the inner ear. Having been predicted by Thomas Gold in 1948, its existence was first demonstrated experimentally by David Kemp in 1978 and otoacoustic emissions have since been shown to arise by a number of different cellular...
- Pure tone audiometryPure tone audiometryPure tone audiometry is the key hearing test used to identify hearing threshold levels of an individual, enabling determination of the degree, type and configuration of a hearing loss. Thus, providing the basis for diagnosis and management. PTA is a subjective, behavioural measurement of hearing...
- Evoked potentialEvoked potentialAn evoked potential is an electrical potential recorded from the nervous system of a human or other animal following presentation of a stimulus, as distinct from spontaneous potentials as detected by electroencephalography or electromyography .Evoked potential amplitudes tend to be low, ranging...