Audiogram

Source: Wikipedia, the free encyclopedia.
For the record label named "Audiogram", see Audiogram (label). For details of animal hearing range, see Hearing range.
Audiogram

An audiogram is a graph that shows the audible threshold for standardized frequencies as measured by an

threshold of hearing, in absolute terms measured in dB
SPL (sound pressure level).

The frequencies displayed on the audiogram are octaves, which represent a doubling in frequency (e.g., 250 Hz, 500 Hz, 1000 Hz, wtc). Commonly tested "inter-octave" frequenices (e.g., 3000 Hz) may also be displayed. The intensities displayed on the audiogram appear as

linear 10 dBHL steps. However, decibels are a logarithimic scale
, so that successive 10 dB increments represent greater increases in loudness.

For humans, normal hearing is between −10 dB(HL) and 15 dB(HL),[2][3] although 0 dB from 250 Hz to 8 kHz is deemed to be 'average' normal hearing.

Hearing thresholds of humans and other

mammals can be found with behavioural hearing tests or physiological tests used in audiometry. For adults, a behavioural hearing test involves a tester who presents tones at specific frequencies (pitches) and intensities (loudnesses
). When the testee hears the sound he or she responds (e.g., by raising a hand or pressing a button. The tester records the lowest intensity sound the testee can hear.

With

audiologist makes a game out of the hearing test by replacing the feedback device with activity-related toys such as blocks or pegs. This is referred to as conditioned play audiometry
. Visual reinforcement audiometry is also used with children. When the child hears the sound, he or she looks in the direction the sound came from and are reinforced with a light and/or animated toy. A similar technique can be used when testing some animals but instead of a toy, food can be used as a reward for responding to the sound.

Physiological tests do not need the patient to respond (Katz 2002). For example, when performing the

otoacoustic emissions
which are generated by a healthy inner ear either spontaneously or evoked by an outside stimulus. In the US, the
NIOSH recommends that people who are regularly exposed to hazardous noise have their hearing tested once a year, or every three years otherwise.[4]

Measurement

Audiograms are produced using a piece of test equipment called an

ANSI standard to a level somewhat higher at 1 kHz.[5]
There are several definitions of the minimal audibility curve, defined in different international standards, and they differ significantly, giving rise to differences in audiograms according to the audiometer used. The ASA-1951 standard for example used a level of 16.5 dB(SPL) at 1 kHz whereas the later ANSI-1969/ISO-1963 standard uses 6.5 dB(SPL), and it is common to allow a 10 dB correction for the older standard.

Audiograms and types of hearing loss

Results of a hearing test plotted on an audiogram illustrating a typical "noise notch" in the left ear
Audiogram showing a typical "noise notch" in the left ear (normal hearing in the right ear)

"Conventional" pure tone audiometry (testing frequencies up to 8 kHz) is the basic measure of hearing status.[6] For research purposes, or early diagnosis of age-related hearing loss, ultra-high frequency audiograms (up to 20 kHz), requiring special audiometer calibration and headphones, can be measured.[7]

Different symbols indicate which ear the response is from and what type of response it is. Results of air conduction audiometry (in which the signals are presented to the ear through headphones, which create vibrations in the air) are reported using circles for the right ear and Xs for the left ear. Results of bone conduction audiometry (in which signals are presented using a vibrator which creates vibrations in the temporal bones of the head in order to bypass the outer and middle ear and test the inner ear and auditory nerve alone) are reporting using brackets. The open edge of the bracket indicates the ear tested, with < or [ representing a right bone conduction threshold and > or ] representing a left bone conduction threshold. When colors are used on an audiogram, red indicates the right ear and blue indicates the left ear.[8][9]

In adults, normal hearing is typically defined as thresholds of 25 dB HL or better (lower).

hearing loss
.

The configuration of thresholds on an audiogram can often help determine the cause(s) of the hearing loss. For example, aging typically leads to hearing thresholds which get poorer as test frequencies get higher.[10] Noise induced hearing loss is typically characterized by a "notch" in the audiogram, with the poorest threshold occurring between 3000 and 6000 Hz (most often 4000 Hz) and better thresholds at lower and higher frequencies.[11]

Hearing impairment may also be the result of certain diseases such as

CMV or Ménière's disease and these can be diagnosed from the shape of the audiogram. Otosclerosis results in an audiogram with significant loss at all frequencies, often of around 40 dB(HL).[12] A deficiency particularly around 2 kHz (termed a Carhart notch in the audiogram) is characteristic of either otosclerosis or a congenital ossicular anomaly.[13] Ménière's disease results in a severe loss at low frequencies.[14]

Constraints

Audiograms are unable to measure hidden hearing loss,[15][16] which is the inability to distinguish between sounds in loud environments such as restaurants. Hidden hearing loss is caused by synaptopathy in the cochlea,[17] as opposed to sensorineural hearing loss caused by hair cell dysfunction. Audiograms are designed to "estimate the softest sounds the patient can detect", and are not reflective of the loud situations that cause difficulties for people with hidden hearing loss. Audiograms may not reflect losses of nerve fibers that respond to loud sounds, key to understanding speech in noisy environments.[18] Research suggests a number of other measures, such as electrocochleography, speech-in-noise perception, and frequency following response, may be more useful.[17]

See also

References

  1. ^ "What is an Audiogram?". www.babyhearing.org. babyhearing.org. Archived from the original on 8 March 2019. Retrieved 7 May 2018.
  2. ISBN 9780683307641. Archived
    from the original on 2021-12-04. Retrieved 2020-11-24.
  3. ISBN 9780133491463
    .
  4. ^ Noise and Hearing Loss Prevention: Frequently Asked Questions. Archived March 4, 2016, at the Wayback Machine NIOSH Safety and Health Topic.
  5. ISBN 9780824790417
    .
  6. ISBN 978-1550092639
    . The most commonly employed measure of auditory status is conventional audiometry (0.5-8 kHz).
  7. ISBN 978-0-12-369391-4
    . For research purposes, or early diagnosis of presbycusis, ultra-high frequency audiograms can be measured. In such cases the test frequencies can go as high as 20 kHz and require special audiometer calibration and headphones.
  8. ^ American Speech-Language-Hearing Association (1990). "Audiometric Symbols [Guidelines]". American Speech-Language-Hearing Association. Retrieved 2022-03-23.
  9. ^ a b Mroz, Mandy (2020-03-10). "How to read an audiogram". Healthy Hearing. Retrieved 2022-03-23.
  10. PMID 32644646
    , retrieved 2022-03-23
  11. PMID 10821155
    .
  12. ^ pure tone audiometry in otosclerosis Archived 2008-12-08 at the Wayback Machine from General Practice Notebook. Retrieved 2012
  13. PMID 21422306
    .
  14. ^ pure tone audiometry in Meniere's disease Archived 2008-12-08 at the Wayback Machine from General Practice Notebook. Retrieved 2012
  15. doi:10.1097/01.HJ.0000459741.56134.79. Archived
    from the original on December 13, 2020. Retrieved November 13, 2020.
  16. PMID 26349143. Archived
    from the original on 1 February 2021. Retrieved 13 December 2020.
  17. ^
    ISSN 2096-5672. Archived
    from the original on 2021-12-04. Retrieved 2020-12-13.
  18. doi:10.1044/leader.ftr1.22072017.48. Archived
    from the original on 2021-12-04. Retrieved 2020-12-13.

Further reading
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