Acoustic reflex

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Acoustic reflex
Blausen 0330 EarAnatomy MiddleEar.png
Identifiers
MeSH D012022
Anatomical terminology

The acoustic reflex (also known as the stapedius reflex, [1] stapedial reflex, [2] auditory reflex, [3] middle-ear-musclereflex (MEM reflex, MEMR), [4] attenuation reflex, [5] cochleostapedial reflex [6] or intra-aural reflex [6] ) is an involuntary muscle contraction that occurs in the middle ear in response to loud sound stimuli or when the person starts to vocalize.

Contents

When presented with an intense sound stimulus, the stapedius and tensor tympani muscles of the ossicles contract. [7] The stapedius stiffens the ossicular chain by pulling the stapes (stirrup) of the middle ear away from the oval window of the cochlea and the tensor tympani muscle stiffens the ossicular chain by loading the tympanic membrane when it pulls the malleus (hammer) in toward the middle ear. The reflex decreases the transmission of vibrational energy to the cochlea, where it is converted into electrical impulses to be processed by the brain.

Acoustic reflex threshold

The acoustic reflex threshold (ART) is the sound pressure level (SPL) from which a sound stimulus with a given frequency will trigger the acoustic reflex. The ART is a function of sound pressure level and frequency.

People with normal hearing have an acoustic reflex threshold (ART) around 70–100 dB SPL. People with conductive hearing loss (i.e., bad transmission in the middle ear) may have a greater or absent acoustic reflex threshold. [8]

The acoustic reflex threshold is usually 10–20 dB below the discomfort threshold. However the discomfort threshold is not a relevant indicator of the harmfulness of a sound: industry workers tend to have a higher discomfort threshold, but the sound is just as harmful to their ears. [9]

The acoustic reflex threshold can be decreased by the simultaneous presentation of a second tone (facilitator). The facilitator tone can be presented to either ear. This facilitation effect tends to be greater when the facilitator tone has a frequency lower than the frequency of the elicitor (i.e. the sound used to trigger the acoustic reflex). [10]

Characteristics and effects

Hypothesized function

The main hypothesized function of the acoustic reflex is the protection of the organ of Corti against excessive stimulation (especially that of the lower frequencies). This protection has been demonstrated both in humans and animals, but with limited effects. [13]

According to the article Significance of the stapedius reflex for the understanding of speech, the latency of contraction is only about 10ms, but maximum tension may not be reached for 100 ms or more. [13] According to the article Le traumatisme acoustique, the latency of contraction is 150 ms with noise stimulus which SPL is at the threshold (ATR), and 25–35 ms at high sound pressure levels. Indeed, the amplitude of the contraction grows with the sound pressure level stimulus. [17]

Because of this latency, the acoustic reflex cannot protect against sudden intense noises. [17] [13] However, when several sudden intense noises are presented at a pace higher than 2–3 seconds of interval, the acoustic reflex is able to play a role against auditory fatigue. [17] [18]

Moreover, the full tension of the stapedius muscle cannot be maintained in response to continued stimulation. Indeed, the tension drops to about 50% of its maximum value after a few seconds. [13]

In damage risk criteria for exposure to impulse noise, the acoustic reflex is integral to the Auditory Hazard Assessment Algorithm for Humans model and the Integrated Cochlear Energy models. These two models estimate the response of the basilar membrane in response to an input stimulus and summate the vibration of the segments of the basilar membrane to predict the potential risk for hearing loss. The acoustic reflex can be activated before an impulse reaches the ear through an assumed conditioned response or it can be activated after the stimulus exceeds a specific level (e.g. 134 dB).

Recent measurements of the acoustic reflex with a group of 50 subjects found that only 2 of the subjects exhibited any pre-activation of the reflex in the warned (countdown) or volitional control of the eliciting stimulus. [19]

An alternative hypothesis for the role of the acoustic reflex is the prevention of auditory masking of high-frequencies by low-frequencies, which are predominant in natural sounds. [20]

Measurement

Most of the time, the stapedius reflex is tested with tympanometry. The contraction of the stapedius muscle stiffens the middle-ear, thus decreasing middle-ear admittance; this can be measured thanks to tympanometry. [8] The acoustic stapedius reflex can also be recorded by means of extratympanic manometry (ETM). [14]

The stapedial reflex can be measured with laser Doppler velocimetry. Jones et al. [19] focused a laser on the light reflex of the manubrium in awake human subjects. The amplitude of a 500 Hz probe tone was used to monitor the vibrations of the tympanic membrane. Various elicitors were presented to the subjects: 1000 Hz tone-burst for 0.5 s at 100 dB SPL, recorded .22 caliber gunshot noise with a peak level of 110 dB SPL. The amplitude of the 500 Hz probe tone was reduced in response to the eliciting stimuli. Time constants for the rate of onset and recovery were measured to be about 113 ms for the tone and 60-69 ms for the gunshot recordings.

Examples of the onset and recovery of the acoustic reflex measured with a laser Doppler velocimetry system. LDV AR measurement USAARL.png
Examples of the onset and recovery of the acoustic reflex measured with a laser Doppler velocimetry system.

As the stapedius muscle is innervated by the facial nerve, [21] a measurement of the reflex can be used to locate the injury on the nerve. If the injury is distal to the stapedius muscle, the reflex is still functional.

A measurement of the reflex can also be used to suggest a retrocochlear lesion (e.g., vestibular schwannoma). [8]

The acoustic reflex normally occurs only at relatively high intensities; contraction of middle ear muscles for quieter sounds can indicate ear dysfunction (e.g. tonic tensor tympani syndrome -TTTS).

The pathway involved in the acoustic reflex is complex and can involve the ossicular chain (malleus, incus and stapes), the cochlea (organ of hearing), the auditory nerve, brain stem, facial nerve, superior olivary complex, and cochlear nucleus. Consequently, the absence of an acoustic reflex, by itself, may not be conclusive in identifying the source of the problem. [21] [19]

See also

Related Research Articles

<span class="mw-page-title-main">Middle ear</span> Portion of the ear internal to the eardrum, and external to the oval window of the inner ear

The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea.

The ossicles are three bones in either middle ear that are among the smallest bones in the human body. They serve to transmit sounds from the air to the fluid-filled labyrinth (cochlea). The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss. The term "ossicle" literally means "tiny bone". Though the term may refer to any small bone throughout the body, it typically refers to the malleus, incus, and stapes of the middle ear.

<span class="mw-page-title-main">Vestibulocochlear nerve</span> Cranial nerve VIII, for hearing and balance

The vestibulocochlear nerve or auditory vestibular nerve, also known as the eighth cranial nerve, cranial nerve VIII, or simply CN VIII, is a cranial nerve that transmits sound and equilibrium (balance) information from the inner ear to the brain. Through olivocochlear fibers, it also transmits motor and modulatory information from the superior olivary complex in the brainstem to the cochlea.

<span class="mw-page-title-main">Otosclerosis</span> Condition characterized by an abnormal bone growth in the middle ear

Otosclerosis is a condition of the middle ear where portions of the dense enchondral layer of the bony labyrinth remodel into one or more lesions of irregularly-laid spongy bone. As the lesions reach the stapes the bone is resorbed, then hardened (sclerotized), which limits its movement and results in hearing loss, tinnitus, vertigo or a combination of symptoms. The term otosclerosis is something of a misnomer: much of the clinical course is characterized by lucent rather than sclerotic bony changes, so the disease is also known as otospongiosis.

<span class="mw-page-title-main">Hearing test</span> Evaluation of the sensitivity of a persons sense of hearing

A hearing test provides an evaluation of the sensitivity of a person's sense of hearing and is most often performed by an audiologist using an audiometer. An audiometer is used to determine a person's hearing sensitivity at different frequencies. There are other hearing tests as well, e.g., Weber test and Rinne test.

<span class="mw-page-title-main">Equal-loudness contour</span> Frequency characteristics of hearing and perceived volume

An equal-loudness contour is a measure of sound pressure level, 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. By definition, two sine waves of differing frequencies are said to have equal-loudness level measured in phons if they are perceived as equally loud by the average young person without significant hearing impairment.

<span class="mw-page-title-main">Sensorineural hearing loss</span> Hearing loss caused by an inner ear or vestibulocochlear nerve defect

Sensorineural hearing loss (SNHL) is a type of hearing loss in which the root cause lies in the inner ear or sensory organ or the vestibulocochlear nerve. SNHL accounts for about 90% of reported hearing loss. SNHL is usually permanent and can be mild, moderate, severe, profound, or total. Various other descriptors can be used depending on the shape of the audiogram, such as high frequency, low frequency, U-shaped, notched, peaked, or flat.

An otoacoustic emission (OAE) is a sound that is generated from within the inner ear. Having been predicted by Austrian astrophysicist Thomas Gold in 1948, its existence was first demonstrated experimentally by British physicist David Kemp in 1978, and otoacoustic emissions have since been shown to arise through a number of different cellular and mechanical causes within the inner ear. Studies have shown that OAEs disappear after the inner ear has been damaged, so OAEs are often used in the laboratory and the clinic as a measure of inner ear health.

<span class="mw-page-title-main">Audiometry</span> Branch of audiology measuring hearing sensitivity

Audiometry is a branch of audiology and the science of measuring hearing acuity for variations in sound intensity and pitch and for tonal purity, 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 distinguish speech from background noise. Acoustic reflex and otoacoustic emissions 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.

Hyperacusis is an increased sensitivity to sound and a low tolerance for environmental noise. Definitions of hyperacusis can vary significantly, but it is often categorized into four subtypes: loudness, pain, annoyance, and fear. It can be a highly debilitating hearing disorder.

Auditory neuropathy (AN) is a hearing disorder in which the outer hair cells of the cochlea are present and functional, but sound information is not transmitted sufficiently by the auditory nerve to the brain. Hearing loss with AN can range from normal hearing sensitivity to profound hearing loss.

Presbycusis, or age-related hearing loss, is the cumulative effect of aging on hearing. It is a progressive and irreversible bilateral symmetrical age-related sensorineural hearing loss resulting from degeneration of the cochlea or associated structures of the inner ear or auditory nerves. The hearing loss is most marked at higher frequencies. Hearing loss that accumulates with age but is caused by factors other than normal aging is not presbycusis, although differentiating the individual effects of distinct causes of hearing loss can be difficult.

<span class="mw-page-title-main">Tensor tympani muscle</span> Muscle of the middle ear

The tensor tympani is a muscle within the middle ear, located in the bony canal above the bony part of the auditory tube, and connects to the malleus bone. Its role is to damp loud sounds, such as those produced from chewing, shouting, or thunder. Because its reaction time is not fast enough, the muscle cannot protect against hearing damage caused by sudden loud sounds, like explosions or gunshots.

<span class="mw-page-title-main">Audiogram</span> Graph showing audible frequencies

An audiogram is a graph that shows the audible threshold for standardized frequencies as measured by an audiometer. The Y axis represents intensity measured in decibels (dB) and the X axis represents frequency measured in hertz (Hz). The threshold of hearing is plotted relative to a standardised curve that represents 'normal' hearing, in dB(HL). They are not the same as equal-loudness contours, which are a set of curves representing equal loudness at different levels, as well as at the threshold of hearing, in absolute terms measured in dB SPL.

<span class="mw-page-title-main">Hearing range</span> Range of frequencies that can be heard by humans or other animals

Hearing range describes the frequency range that can be heard by humans or other animals, though it can also refer to the range of levels. The human range is commonly given as 20 to 20,000 Hz, although there is considerable variation between individuals, especially at high frequencies, and a gradual loss of sensitivity to higher frequencies with age is considered normal. Sensitivity also varies with frequency, as shown by equal-loudness contours. Routine investigation for hearing loss usually involves an audiogram which shows threshold levels relative to a normal.

The auditory brainstem response (ABR), also called brainstem evoked response audiometry (BERA), is an auditory evoked potential extracted from ongoing electrical activity in the brain and recorded via electrodes placed on the scalp. The measured recording is a series of six to seven vertex positive waves of which I through V are evaluated. These waves, labeled with Roman numerals in Jewett and Williston convention, occur in the first 10 milliseconds after onset of an auditory stimulus. The ABR is considered an exogenous response because it is dependent upon external factors.

<span class="mw-page-title-main">Pure-tone audiometry</span>

Pure-tone audiometry is the main hearing test used to identify hearing threshold levels of an individual, enabling determination of the degree, type and configuration of a hearing loss and thus providing a basis for diagnosis and management. Pure-tone audiometry is a subjective, behavioural measurement of a hearing threshold, as it relies on patient responses to pure tone stimuli. Therefore, pure-tone audiometry is only used on adults and children old enough to cooperate with the test procedure. As with most clinical tests, standardized calibration of the test environment, the equipment and the stimuli is needed before testing proceeds. Pure-tone audiometry only measures audibility thresholds, rather than other aspects of hearing such as sound localization and speech recognition. However, there are benefits to using pure-tone audiometry over other forms of hearing test, such as click auditory brainstem response (ABR). Pure-tone audiometry provides ear specific thresholds, and uses frequency specific pure tones to give place specific responses, so that the configuration of a hearing loss can be identified. As pure-tone audiometry uses both air and bone conduction audiometry, the type of loss can also be identified via the air-bone gap. Although pure-tone audiometry has many clinical benefits, it is not perfect at identifying all losses, such as ‘dead regions’ of the cochlea and neuropathies such as auditory processing disorder (APD). This raises the question of whether or not audiograms accurately predict someone's perceived degree of disability.

In audio signal processing, auditory masking occurs when the perception of one sound is affected by the presence of another sound.

<span class="mw-page-title-main">Hearing</span> Sensory perception of sound by living organisms

Hearing, or auditory perception, is the ability to perceive sounds through an organ, such as an ear, by detecting vibrations as periodic changes in the pressure of a surrounding medium. The academic field concerned with hearing is auditory science.

The neural encoding of sound is the representation of auditory sensation and perception in the nervous system. The complexities of contemporary neuroscience are continually redefined. Thus what is known of the auditory system has been continually changing. The encoding of sounds includes the transduction of sound waves into electrical impulses along auditory nerve fibers, and further processing in the brain.

References

  1. ↑ Davies, R. A. (2016-01-01), Furman, Joseph M.; Lempert, Thomas (eds.), "Chapter 11 - Audiometry and other hearing tests", Handbook of Clinical Neurology, Neuro-Otology, Elsevier, 137: 157–176, doi:10.1016/B978-0-444-63437-5.00011-X, ISBN   9780444634375, PMID   27638069 , retrieved 2020-01-05
  2. ↑ "Abnormality of the acoustic reflex (Concept Id: C4022426) - MedGen - NCBI". www.ncbi.nlm.nih.gov. Retrieved 2020-01-05.
  3. ↑ "Definition of auditory reflex | Dictionary.com". www.dictionary.com. Retrieved 2020-01-05.
  4. ↑ Eggermont, Jos J. (2017-01-01), Eggermont, Jos J. (ed.), "Chapter 5 - Types of Hearing Loss", Hearing Loss, Academic Press, pp. 129–173, ISBN   978-0-12-805398-0 , retrieved 2020-01-05
  5. ↑ Bear, Mark F.; Connors, Barry W.; Paradiso, Michael A. (2007). Neuroscience. Lippincott Williams & Wilkins. p. 350. ISBN   978-0-7817-6003-4.
  6. 1 2 Stach, Brad A. (2019-02-22). Comprehensive Dictionary of Audiology: Illustrated, Third Edition. Plural Publishing. p. 225. ISBN   978-1-944883-90-4.
  7. ↑ Fox, Stuart (2006). Human Physiology (ninth ed.). New York: McGraw-Hill. pp.  267–9. ISBN   978-0-07-285293-6.
  8. 1 2 3 4 "Impedance Audiometry". MedScape. 2018-09-12.
  9. ↑ W. Niemeyer (1971). "Relations between the Discomfort Level and the Reflex Threshold of the Middle Ear Muscles". International Journal of Audiology. 10 (3): 172–176. doi:10.3109/00206097109072555. PMID   5163659.
  10. ↑ Kawase, Tetsuaki; Takasaka, Tomonori; Hidaka, Hiroshi (June 1997). "Frequency summation observed in the human acoustic reflex". Hearing Research. 108 (1–2): 37–45. doi:10.1016/s0378-5955(97)00039-7. PMID   9213120. S2CID   20541412.
  11. ↑ "Notes on the Acoustic Middle Ear Reflex". American academy of audiology. 2014-05-12. Archived from the original on 2022-12-05. Retrieved 2015-03-01.
  12. ↑ Flamme, Gregory A.; Deiters, Kristy K.; Tasko, Stephen M.; Ahroon, William A. (2017). "Acoustic reflexes are common but not pervasive: Evidence from the national Health and Nutrition Examination Survey, 1999-2012". Int J Audiol. 56 (sup1): S52–S62. doi:10.1080/14992027.2016.1257164. PMID   27869511. S2CID   26258703.
  13. 1 2 3 4 5 G. Lidén; J. E. Hawkins; B. Nordlund (1964). "Significance of the Stapedius Reflex for the Understanding of Speech". Acta Oto-Laryngologica. 57: 275–279. doi:10.3109/00016486409134576. PMID   14146685.
  14. 1 2 Brask, Torben (1978). "The Noise Protection Effect of the Stapedius Reflex". Acta Oto-Laryngologica. 86: 116–117. doi:10.3109/00016487809123490. PMID   287319.
  15. 1 2 Møller, Aage (2000). Hearing: It's Physiology and Pathophysiology (illustrated ed.). Academic Press. pp. 181–90. ISBN   978-0125042550.
  16. ↑ Borg, E; Counter, S A (1989). "The Middle-Ear Muscles". Scientific American . 261 (2): 74–78. Bibcode:1989SciAm.261b..74B. doi:10.1038/scientificamerican0889-74. PMID   2667133.
  17. 1 2 3 Dancer, Armand (1991). "Le traumatisme acoustique". Médecine/Sciences (in French). 7 (4): 357–367. doi: 10.4267/10608/4361 .
  18. ↑ "Dr Stella Fulman". Thursday, April 23, 2020
  19. 1 2 3 Jones, Heath G.; Nathaniel T. Greene; William A. Ahroon (2018). "Human middle-ear muscles contract in anticipation of acoustic impulses: Implications for hearing risk assessments". Hearing Research. 378: 53–62. doi:10.1016/j.heares.2018.11.006. PMID   30538053. S2CID   54445405.
  20. ↑ Pang, XD; Guinan, JJ (1997). "Effects of stapedius-muscle contractions on the masking of auditory-nerve responses". J Acoust Soc Am. 102 (6): 3576–86. Bibcode:1997ASAJ..102.3576P. doi: 10.1121/1.420399 . PMID   9407651.
  21. 1 2 Probst, Rudolf; Gerhard Grevers; Heinrich Iro (2006). Basic Otorhinolaryngology: A Step-by-Step Learning Guide (second, illustrated, revised ed.). Thieme. pp.  185–6. ISBN   978-1588903372.
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