Hearing

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Video showing how sounds make their way from the source to the brain

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. [1] The academic field concerned with hearing is auditory science.

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Sound may be heard through solid, liquid, or gaseous matter. [2] It is one of the traditional five senses. Partial or total inability to hear is called hearing loss.

In humans and other vertebrates, hearing is performed primarily by the auditory system: mechanical waves, known as vibrations, are detected by the ear and transduced into nerve impulses that are perceived by the brain (primarily in the temporal lobe). Like touch, audition requires sensitivity to the movement of molecules in the world outside the organism. Both hearing and touch are types of mechanosensation. [3] [4]

Hearing mechanism

There are three main components of the human auditory system: the outer ear, the middle ear, and the inner ear.

Outer ear

Schematic diagram of the human ear Tidens naturlaere fig40.png
Schematic diagram of the human ear

The outer ear includes the pinna, the visible part of the ear, as well as the ear canal, which terminates at the eardrum, also called the tympanic membrane. The pinna serves to focus sound waves through the ear canal toward the eardrum. Because of the asymmetrical character of the outer ear of most mammals, sound is filtered differently on its way into the ear depending on the location of its origin. This gives these animals the ability to localize sound vertically. The eardrum is an airtight membrane, and when sound waves arrive there, they cause it to vibrate following the waveform of the sound. Cerumen (ear wax) is produced by ceruminous and sebaceous glands in the skin of the human ear canal, protecting the ear canal and tympanic membrane from physical damage and microbial invasion. [5]

Middle ear

The middle ear uses three tiny bones, the malleus, the incus, and the stapes, to convey vibrations from the eardrum to the inner ear. Gray919.png
The middle ear uses three tiny bones, the malleus, the incus, and the stapes, to convey vibrations from the eardrum to the inner ear.

The middle ear consists of a small air-filled chamber that is located medial to the eardrum. Within this chamber are the three smallest bones in the body, known collectively as the ossicles which include the malleus, incus, and stapes (also known as the hammer, anvil, and stirrup, respectively). They aid in the transmission of the vibrations from the eardrum into the inner ear, the cochlea. The purpose of the middle ear ossicles is to overcome the impedance mismatch between air waves and cochlear waves, by providing impedance matching.

Also located in the middle ear are the stapedius muscle and tensor tympani muscle, which protect the hearing mechanism through a stiffening reflex. The stapes transmits sound waves to the inner ear through the oval window, a flexible membrane separating the air-filled middle ear from the fluid-filled inner ear. The round window, another flexible membrane, allows for the smooth displacement of the inner ear fluid caused by the entering sound waves.

Inner ear

The inner ear is a small but very complex organ. Right osseous labyrinth svg hariadhi.svg
The inner ear is a small but very complex organ.

The inner ear consists of the cochlea, which is a spiral-shaped, fluid-filled tube. It is divided lengthwise by the organ of Corti, which is the main organ of mechanical to neural transduction. Inside the organ of Corti is the basilar membrane, a structure that vibrates when waves from the middle ear propagate through the cochlear fluid – endolymph. The basilar membrane is tonotopic, so that each frequency has a characteristic place of resonance along it. Characteristic frequencies are high at the basal entrance to the cochlea, and low at the apex. Basilar membrane motion causes depolarization of the hair cells, specialized auditory receptors located within the organ of Corti. [6] While the hair cells do not produce action potentials themselves, they release neurotransmitter at synapses with the fibers of the auditory nerve, which does produce action potentials. In this way, the patterns of oscillations on the basilar membrane are converted to spatiotemporal patterns of firings which transmit information about the sound to the brainstem. [7]

Neuronal

The lateral lemnisci (red) connects lower brainstem auditory nuclei to the inferior colliculus in the midbrain. Lateral lemniscus.PNG
The lateral lemnisci (red) connects lower brainstem auditory nuclei to the inferior colliculus in the midbrain.

The sound information from the cochlea travels via the auditory nerve to the cochlear nucleus in the brainstem. From there, the signals are projected to the inferior colliculus in the midbrain tectum. The inferior colliculus integrates auditory input with limited input from other parts of the brain and is involved in subconscious reflexes such as the auditory startle response.

The inferior colliculus in turn projects to the medial geniculate nucleus, a part of the thalamus where sound information is relayed to the primary auditory cortex in the temporal lobe. Sound is believed to first become consciously experienced at the primary auditory cortex. Around the primary auditory cortex lies Wernickes area, a cortical area involved in interpreting sounds that is necessary to understand spoken words.

Disturbances (such as stroke or trauma) at any of these levels can cause hearing problems, especially if the disturbance is bilateral. In some instances it can also lead to auditory hallucinations or more complex difficulties in perceiving sound.

Hearing tests

Hearing can be measured by behavioral tests using an audiometer. Electrophysiological tests of hearing can provide accurate measurements of hearing thresholds even in unconscious subjects. Such tests include auditory brainstem evoked potentials (ABR), otoacoustic emissions (OAE) and electrocochleography (ECochG). Technical advances in these tests have allowed hearing screening for infants to become widespread.

Hearing can be measured by mobile applications which includes audiological hearing test function or hearing aid application. These applications allow the user to measure hearing thresholds at different frequencies (audiogram). Despite possible errors in measurements, hearing loss can be detected. [8] [9]

Hearing loss

There are several different types of hearing loss: conductive hearing loss, sensorineural hearing loss and mixed types. Recently, the term of Aural Diversity has come into greater use, to communicate hearing loss and differences in a less negatively-associated term.

There are defined degrees of hearing loss: [10] [11]

Causes

Prevention

Hearing protection is the use of devices designed to prevent noise-induced hearing loss (NIHL), a type of post-lingual hearing impairment. The various means used to prevent hearing loss generally focus on reducing the levels of noise to which people are exposed. One way this is done is through environmental modifications such as acoustic quieting, which may be achieved with as basic a measure as lining a room with curtains, or as complex a measure as employing an anechoic chamber, which absorbs nearly all sound. Another means is the use of devices such as earplugs, which are inserted into the ear canal to block noise, or earmuffs, objects designed to cover a person's ears entirely.

Management

The loss of hearing, when it is caused by neural loss, cannot presently be cured. Instead, its effects can be mitigated by the use of audioprosthetic devices, i.e. hearing assistive devices such as hearing aids and cochlear implants. In a clinical setting, this management is offered by otologists and audiologists.

Relation to health

Hearing loss is associated with Alzheimer's disease and dementia with a greater degree of hearing loss tied to a higher risk. [12] There is also an association between type 2 diabetes and hearing loss. [13]

Hearing underwater

Hearing threshold and the ability to localize sound sources are reduced underwater in humans, but not in aquatic animals, including whales, seals, and fish which have ears adapted to process water-borne sound. [14] [15]

In vertebrates

A cat can hear high-frequency sounds up to two octaves higher than a human. Domestic cat felis catus.jpg
A cat can hear high-frequency sounds up to two octaves higher than a human.

Not all sounds are normally audible to all animals. Each species has a range of normal hearing for both amplitude and frequency. Many animals use sound to communicate with each other, and hearing in these species is particularly important for survival and reproduction. In species that use sound as a primary means of communication, hearing is typically most acute for the range of pitches produced in calls and speech.

Frequency range

Frequencies capable of being heard by humans are called audio or sonic. The range is typically considered to be between 20 Hz and 20,000 Hz. [16] Frequencies higher than audio are referred to as ultrasonic, while frequencies below audio are referred to as infrasonic. Some bats use ultrasound for echolocation while in flight. Dogs are able to hear ultrasound, which is the principle of 'silent' dog whistles. Snakes sense infrasound through their jaws, and baleen whales, giraffes, dolphins and elephants use it for communication. Some fish have the ability to hear more sensitively due to a well-developed, bony connection between the ear and their swim bladder. This "aid to the deaf" for fishes appears in some species such as carp and herring. [17]

Time discrimination

Human perception of audio signal time separation has been measured to less than 10 microseconds (10μs). This does not mean that frequencies above 100 kHz are audible, but that time discrimination is not directly coupled with frequency range. Georg Von Békésy in 1929 identifying sound source directions suggested humans can resolve timing differences of 10μs or less. In 1976 Jan Nordmark's research indicated inter-aural resolution better than 2μs. [18] Milind Kuncher's 2007 research resolved time misalignment to under 10μs. [19]

In birds

This section is an excerpt from Bird anatomy § Hearing.[ edit ]
The avian ear is adapted to pick up on slight and rapid changes of pitch found in bird song. General avian tympanic membrane form is ovular and slightly conical. Morphological differences in the middle ear are observed between species. Ossicles within green finches, blackbirds, song thrushes, and house sparrows are proportionately shorter to those found in pheasants, Mallard ducks, and sea birds. In song birds, a syrinx allows the respective possessors to create intricate melodies and tones. The middle avian ear is made up of three semicircular canals, each ending in an ampulla and joining to connect with the macula sacculus and lagena, of which the cochlea, a straight short tube to the external ear, branches from. [20]

In invertebrates

Even though they do not have ears, invertebrates have developed other structures and systems to decode vibrations traveling through the air, or “sound”. Charles Henry Turner was the first scientist to formally show this phenomenon through rigorously controlled experiments in ants. [21] Turner ruled out the detection of ground vibration and suggested that other insects likely have auditory systems as well.

Many insects detect sound through the way air vibrations deflect hairs along their body. Some insects have even developed specialized hairs tuned to detecting particular frequencies, such as certain caterpillar species that have evolved hair with properties such that it resonates most with the sound of buzzing wasps, thus warning them of the presence of natural enemies. [22]

Some insects possess a tympanal organ. These are "eardrums", that cover air filled chambers on the legs. Similar to the hearing process with vertebrates, the eardrums react to sonar waves. Receptors that are placed on the inside translate the oscillation into electric signals and send them to the brain. Several groups of flying insects that are preyed upon by echolocating bats can perceive the ultrasound emissions this way and reflexively practice ultrasound avoidance.

See also

Basics
General
Disorders
Test and measurement

Related Research Articles

<span class="mw-page-title-main">Inner ear</span> Innermost part of the vertebrate ear

The inner ear is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:

<span class="mw-page-title-main">Middle ear</span> Portion of the ear

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

<span class="mw-page-title-main">Cochlea</span> Snail-shaped part of inner ear involved in hearing

The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the organ of Corti, the sensory organ of hearing, which is distributed along the partition separating the fluid chambers in the coiled tapered tube of the cochlea.

<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">Basilar membrane</span> Inner ear structure

The basilar membrane is a stiff structural element within the cochlea of the inner ear which separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani. The basilar membrane moves up and down in response to incoming sound waves, which are converted to traveling waves on the basilar membrane.

<span class="mw-page-title-main">Organ of Corti</span> Receptor organ for hearing

The organ of Corti, or spiral organ, is the receptor organ for hearing and is located in the mammalian cochlea. This highly varied strip of epithelial cells allows for transduction of auditory signals into nerve impulses' action potential. Transduction occurs through vibrations of structures in the inner ear causing displacement of cochlear fluid and movement of hair cells at the organ of Corti to produce electrochemical signals.

In physiology, transduction is the translation of arriving stimulus into an action potential by a sensory receptor. It begins when stimulus changes the membrane potential of a sensory receptor.

<span class="mw-page-title-main">Auditory system</span> Sensory system used for hearing

The auditory system is the sensory system for the sense of hearing. It includes both the sensory organs and the auditory parts of the sensory system.

<span class="mw-page-title-main">Ear</span> Organ of hearing and balance

An ear is the organ that enables hearing and body balance using the vestibular system. In mammals, the ear is usually described as having three parts: the outer ear, the middle ear and the inner ear. The outer ear consists of the pinna and the ear canal. Since the outer ear is the only visible portion of the ear in most animals, the word "ear" often refers to the external part alone. The middle ear includes the tympanic cavity and the three ossicles. The inner ear sits in the bony labyrinth, and contains structures which are key to several senses: the semicircular canals, which enable balance and eye tracking when moving; the utricle and saccule, which enable balance when stationary; and the cochlea, which enables hearing. The ear canal is cleaned via earwax, which naturally migrates to the auricle. The ears of vertebrates are placed somewhat symmetrically on either side of the head, an arrangement that aids sound localization.

<span class="mw-page-title-main">Acoustic reflex</span> Small muscle contraction in the middle ear in response to loud sound

The acoustic reflex is an involuntary muscle contraction that occurs in the middle ear in response to loud sound stimuli or when the person starts to vocalize.

<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, 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.

<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.

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.

In audiology and psychoacoustics the concept of critical bands, introduced by Harvey Fletcher in 1933 and refined in 1940, describes the frequency bandwidth of the "auditory filter" created by the cochlea, the sense organ of hearing within the inner ear. Roughly, the critical band is the band of audio frequencies within which a second tone will interfere with the perception of the first tone by auditory masking.

Binaural fusion or binaural integration is a cognitive process that involves the combination of different auditory information presented binaurally, or to each ear. In humans, this process is essential in understanding speech in noisy and reverberent environments.

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.

Electrocochleography is a technique of recording electrical potentials generated in the inner ear and auditory nerve in response to sound stimulation, using an electrode placed in the ear canal or tympanic membrane. The test is performed by an otologist or audiologist with specialized training, and is used for detection of elevated inner ear pressure or for the testing and monitoring of inner ear and auditory nerve function during surgery.

Bone-conduction auditory brainstem response or BCABR is a type of auditory evoked response that records neural response from EEG with stimulus transmitted through bone conduction.

Cochlea is Latin for “snail, shell or screw” and originates from the Greek word κοχλίας kokhlias. The modern definition, the auditory portion of the inner ear, originated in the late 17th century. Within the mammalian cochlea exists the organ of Corti, which contains hair cells that are responsible for translating the vibrations it receives from surrounding fluid-filled ducts into electrical impulses that are sent to the brain to process sound.

<span class="mw-page-title-main">Sound localization in owls</span> Ability of owls to locate sounds in 3D space

Most owls are nocturnal or crepuscular birds of prey. Because they hunt at night, they must rely on non-visual senses. Experiments by Roger Payne have shown that owls are sensitive to the sounds made by their prey, not the heat or the smell. In fact, the sound cues are both necessary and sufficient for localization of mice from a distant location where they are perched. For this to work, the owls must be able to accurately localize both the azimuth and the elevation of the sound source.

References

  1. ↑ Plack, C. J. (2014). The Sense of Hearing. Psychology Press Ltd. ISBN   978-1848725157.
  2. ↑ Jan Schnupp; Israel Nelken; Andrew King (2011). Auditory Neuroscience. MIT Press. ISBN   978-0-262-11318-2. Archived from the original on 2011-01-29. Retrieved 2011-04-13.
  3. ↑ Kung C. (2005-08-04). "A possible unifying principle for mechanosensation". Nature. 436 (7051): 647–654. Bibcode:2005Natur.436..647K. doi:10.1038/nature03896. PMID   16079835. S2CID   4374012.
  4. ↑ Peng, AW.; Salles, FT.; Pan, B.; Ricci, AJ. (2011). "Integrating the biophysical and molecular mechanisms of auditory hair cell mechanotransduction". Nat Commun. 2: 523. Bibcode:2011NatCo...2..523P. doi:10.1038/ncomms1533. PMC   3418221 . PMID   22045002.
  5. ↑ Gelfand, Stanley A. (2009). Essentials of audiology (3rd ed.). New York: Thieme. ISBN   978-1-60406-044-7. OCLC   276814877.
  6. ↑ Daniel Schacter; Daniel Gilbert; Daniel Wegner (2011). "Sensation and Perception". In Charles Linsmeiser (ed.). Psychology . Worth Publishers. pp.  158–159. ISBN   978-1-4292-3719-2.
  7. ↑ William Yost (2003). "Audition". In Alice F. Healy; Robert W. Proctor (eds.). Handbook of Psychology: Experimental psychology. John Wiley and Sons. p. 130. ISBN   978-0-471-39262-0.
  8. ↑ Shojaeemend, Hassan; Ayatollahi, Haleh (2018). "Automated Audiometry: A Review of the Implementation and Evaluation Methods". Healthcare Informatics Research. 24 (4): 263–275. doi:10.4258/hir.2018.24.4.263. ISSN   2093-3681. PMC   6230538 . PMID   30443414.
  9. ↑ Keidser, Gitte; Convery, Elizabeth (2016-04-12). "Self-Fitting Hearing Aids". Trends in Hearing. 20: 233121651664328. doi:10.1177/2331216516643284. ISSN   2331-2165. PMC   4871211 . PMID   27072929.
  10. ↑ "Definition of hearing loss - hearing loss classification". hear-it.org. Archived from the original on 2021-06-28. Retrieved 2013-08-07.
  11. ↑ Martini A, Mazzoli M, Kimberling W (December 1997). "An introduction to the genetics of normal and defective hearing". Ann. N. Y. Acad. Sci. 830 (1): 361–74. Bibcode:1997NYASA.830..361M. doi:10.1111/j.1749-6632.1997.tb51908.x. PMID   9616696. S2CID   7209008.
  12. ↑ Thomson, Rhett S.; Auduong, Priscilla; Miller, Alexander T.; Gurgel, Richard K. (2017-03-16). "Hearing loss as a risk factor for dementia: A systematic review". Laryngoscope Investigative Otolaryngology. 2 (2): 69–79. doi:10.1002/lio2.65. ISSN   2378-8038. PMC   5527366 . PMID   28894825.
  13. ↑ Akinpelu, Olubunmi V.; Mujica-Mota, Mario; Daniel, Sam J. (2014). "Is type 2 diabetes mellitus associated with alterations in hearing? A systematic review and meta-analysis". The Laryngoscope. 124 (3): 767–776. doi:10.1002/lary.24354. ISSN   1531-4995. PMID   23945844. S2CID   25569962.
  14. ↑ "Discovery of Sound in the Sea". University of Rhode Island. 2019.
  15. ↑ Au, W.L (2000). Hearing by Whales and Dolphins. Springer. p. 485. ISBN   978-0-387-94906-2.
  16. ↑ D'Ambrose, Christoper; Choudhary, Rizwan (2003). Elert, Glenn (ed.). "Frequency range of human hearing". The Physics Factbook. Retrieved 2022-01-22.
  17. ↑ Williams, C. B. (1941). "Sense of Hearing in Fishes". Nature. 147 (3731): 543. Bibcode:1941Natur.147..543W. doi: 10.1038/147543b0 . ISSN   0028-0836. S2CID   4095706.
  18. ↑ Robjohns, Hugh (August 2016). "MQA Time-domain Accuracy & Digital Audio Quality". soundonsound.com. Sound On Sound. Archived from the original on 10 March 2023.
  19. ↑ Kuncher, Milind (August 2007). "Audibility of temporal smearing and time misalignment of acoustic signals" (PDF). boson.physics.sc.edu. Archived (PDF) from the original on 14 July 2014.
  20. ↑ Mills, Robert (March 1994). "Applied comparative anatomy of the avian middle ear". Journal of the Royal Society of Medicine. 87 (3): 155–6. doi:10.1177/014107689408700314. PMC   1294398 . PMID   8158595.
  21. ↑ Turner CH. 1923. The homing of the Hymenoptera. Trans. Acad. Sci. St. Louis 24: 27–45
  22. ↑ Tautz, Jürgen, and Michael Rostás. "Honeybee buzz attenuates plant damage by caterpillars." Current Biology 18, no. 24 (2008): R1125-R1126.

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