Hearing, or auditory perception, is the ability to perceive sounds by detecting vibrations,[1] changes in the pressure of the surrounding medium through time, through an organ such as the ear. The academic field concerned with hearing is auditory science.

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]

How sounds make their way from the source to your brain
Tidens naturlære fig40
Schematic diagram of the human ear

Hearing mechanism

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

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

Outer 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 what vertical location it is coming from. 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.

Middle 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.

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.[5] 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.[6]


Lateral lemniscus
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.

Defense mechanism

The hearing structures of many species have defense mechanisms against injury. For example, the muscles of the middle ear (e.g. the stapedius muscle) in many mammals contract reflexively in reaction to loud sounds which may otherwise injure the hearing ability of the organism.

Hearing loss

There are several different types of hearing loss: Conductive hearing loss, sensorineural hearing loss and mixed types.

  • Conductive hearing loss
  • Sensorineural hearing loss
  • Mixed hearing loss

There are defined degrees of hearing loss:[7][8]

  • Mild hearing loss - People with mild hearing loss have difficulties keeping up with conversations, especially in noisy surroundings. The most quiet sounds that people with mild hearing loss can hear with their better ear are between 25 and 40 dB HL.
  • Moderate hearing loss - People with moderate hearing loss have difficulty keeping up with conversations when they are not using a hearing aid. On average, the most quiet sounds heard by people with moderate hearing loss with their better ear are between 40 and 70 dB HL.
  • Severe hearing loss - People with severe hearing loss depend on powerful hearing aid. However, they often rely on lip-reading even when they are using hearing aids. The most quiet sounds heard by people with severe hearing loss with their better ear are between 70 and 95 dB HL.
  • Profound hearing loss - People with profound hearing loss are very hard of hearing and they mostly rely on lip-reading and sign language. The most quiet sounds heard by people with profound hearing loss with their better ear are from 95 dB HL or more.


  • Heredity
  • Congenital conditions
  • Presbycusis
  • Acquired
    • Noise-induced hearing loss
    • Ototoxic drugs and chemicals
    • Infection


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.


  • Hearing aids are electronic devices that enable a person with hearing loss to receive sounds at certain amplitudes. This technological development has led to the benefit of improving the sense of hearing of a person, but the usage of these devices is significantly low. Psychologically, the first time that a person realizes that he/she needs help from a professional such as an audiologist is when they feel that their hearing is severely poor. Initially, people don't like to believe that they are becoming deaf; hence it negatively affects their approach towards the use of hearing aids. Familiarity with the devices and consultation with professionals do help people feel good about using the hearing aids.[9]

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 fishes which have ears adapted to process water borne sound.[10] [11][12] Some research suggests underwater hearing in humans may occur through bone conduction but with poor localization. This is related to differences of the speed of sound in water vs air and the blocking of normal air conducted sound paths.[13]

In vertebrates

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.[14] 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. The "aid to the deaf" of fishes appears in some species such as carp and herring.[15]

In invertebrates

Vertebrates aren't the only group of animals that have hearing. Some insects have hearing organs as well (e.g. the long-horned grasshopper, lubber grasshopper and the cicada); they use sound as a form of communication.

Something widely spread among insects is body hair, that can be made to swing by sonar waves. Due to the resonance phenomenon certain hairs swing stronger when exposed to a specific sonar-frequency. This specificity depends on the stiffness and the length of the hairs. That is why certain caterpillar species have evolved hair that would resonate with the sound of buzzing wasps, thus warning them of the presence of natural enemies. Moreover, mosquitoes have hair on their antennae that resonate with the flying sound of homogeneous females, enabling the males the ability to detect potential sexual partners.

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.


The basilar membrane of the inner ear spreads out different frequencies: high frequencies produce a large vibration at the end near the middle ear (the "base"), and low frequencies a large vibration at the distant end (the "apex"). Thus the ear performs a sort of frequency analysis, roughly similar to a Fourier transform.[16][17] However, the nerve pulses delivered to the brain contain both rate-versus-place and fine temporal structure information, so the similarity is not strong.

See also



Test and measurement



  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.
  3. ^ Kung C. (2005-08-04). "A possible unifying principle for mechanosensation". Nature. 436 (7051): 647–654. doi:10.1038/nature03896. PMID 16079835.
  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. doi:10.1038/ncomms1533. PMC 3418221. PMID 22045002.
  5. ^ Daniel Schacter; Daniel Gilbert; Daniel Wegner (2011). "Sensation and Perception". In Charles Linsmeiser. Psychology. Worth Publishers. pp. 158–159. ISBN 978-1-4292-3719-2.
  6. ^ William Yost (2003). "Audition". In Alice F. Healy; Robert W. Proctor. Handbook of Psychology: Experimental psychology. John Wiley and Sons. p. 130. ISBN 978-0-471-39262-0.
  7. ^ "Definition of hearing loss - hearing loss classification". hear-it.org.
  8. ^ Martini A, Mazzoli M, Kimberling W (December 1997). "An introduction to the genetics of normal and defective hearing". Ann. N. Y. Acad. Sci. 830: 361–74. doi:10.1111/j.1749-6632.1997.tb51908.x. PMID 9616696.
  9. ^ Vestergaard Knudsen, L.; Oberg, M.; Nielsen, C.; Naylor, G.; Kramer, S. E. (2010). "Factors Influencing Help Seeking, Hearing Aid Uptake, Hearing Aid Use and Satisfaction With Hearing Aids: A Review of the Literature". Trends in Amplification. 14 (3): 127–154. doi:10.1177/1084713810385712. ISSN 1084-7138. PMC 4111466. PMID 21109549.
  10. ^ "Discovery of Sound in the Sea".
  11. ^ Au, W.L (2000). Hearing by Whales and Dolphins. Springer. p. 485. ISBN 978-0-387-94906-2.
  12. ^ Graham, Michael (1941). "Sense of Hearing in Fishes". Nature. 147 (3738): 779. doi:10.1038/147779b0.
  13. ^ Shupak A. Sharoni Z. Yanir Y. Keynan Y. Alfie Y. Halpern P. (January 2005). "Underwater Hearing and Sound Localization with and without an Air Interface". Otology & Neurotology. 26 (1): 127–130. doi:10.1097/00129492-200501000-00023.
  14. ^ "Frequency Range of Human Hearing". The Physics Factbook.
  15. ^ Williams, C. B. (1941). "Sense of Hearing in Fishes". Nature. 147 (3731): 543. doi:10.1038/147543b0. ISSN 0028-0836.
  16. ^ Deutsch, Diana (1999). The psychology of music. Gulf Professional Publishing. p. 153. ISBN 978-0-12-213565-1. Retrieved 24 May 2011.
  17. ^ Hauser, Marc D. (1998). The evolution of communication. MIT Press. p. 190. ISBN 978-0-262-58155-4. Retrieved 24 May 2011.

Further reading

External links


Audiology (from Latin audīre, "to hear"; and from Greek -λογία, -logia) is a branch of science that studies hearing, balance, and related disorders. Audiologists treat those with hearing loss and proactively prevent related damage. By employing various testing strategies (e.g. behavioral hearing tests, otoacoustic emission measurements, and electrophysiologic tests), audiologists aim to determine whether someone has normal sensitivity to sounds. If hearing loss is identified, audiologists determine which portions of hearing (high, middle, or low frequencies) are affected, to what degree (severity of loss), and where the lesion causing the hearing loss is found (outer ear, middle ear, inner ear, auditory nerve and/or central nervous system). If an audiologist determines that a hearing loss or vestibular abnormality is present he or she will provide recommendations for interventions or rehabilitation (e.g. hearing aids, cochlear implants, appropriate medical referrals).

In addition to diagnosing audiologic and vestibular pathologies, audiologists can also specialize in rehabilitation of tinnitus, hyperacusis, misophonia, auditory processing disorders, cochlear implant use and/or hearing aid use. Audiologists can provide hearing health care from birth to end-of-life.

Bardo Thodol

The Bardo Thodol (Tibetan: བར་དོ་ཐོས་གྲོལ, Wylie: bar do thos grol, "Liberation Through Hearing During the Intermediate State") is a text from a larger corpus of teachings, the Profound Dharma of Self-Liberation through the Intention of the Peaceful and Wrathful Ones, revealed by Karma Lingpa (1326–1386). It is the best-known work of Nyingma literature, and is known in the West as the Tibetan Book of the Dead.

The Tibetan text describes, and is intended to guide one through, the experiences that the consciousness has after death, in the bardo, the interval between death and the next rebirth. The text also includes chapters on the signs of death and rituals to undertake when death is closing in or has taken place.


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 turns(full) and a 3/4(3 quarters) turn 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 fluid chambers in the coiled tapered tube of the cochlea.

The name cochlea derives from Ancient Greek κοχλίας (kōhlias), meaning 'spiral, snail shell'.

Cochlear implant

A cochlear implant (CI) is a surgically implanted neuroprosthetic device that provides a sense of sound to a person with moderate to profound sensorineural hearing loss. Cochlear implants bypass the normal acoustic hearing process, instead replacing it with electric hearing. Namely, the sound sensation comes from the sound that is converted to electric signals which directly stimulate the auditory nerve. The brain adapts to the new mode of hearing, and eventually can interpret the electric signals as sound and speech.

The implant has two main components. The outside component is generally worn behind the ear, but could also be attached to clothing, for example, in young children. This component, the sound processor, contains microphones, electronics that include DSP chips, battery, and a coil which transmits a signal to the implant across the skin. The inside component, the actual implant, has a coil to receive signals, electronics, and an array of electrodes which is placed into the cochlea, which stimulate the cochlear nerve.

The surgical procedure is performed under general anesthesia. Surgical risks are minimal but can include tinnitus and dizziness.

From the early days of implants in the 1970s and the 1980s, speech perception via an implant has steadily increased. Many users of modern implants gain reasonable to good hearing and speech perception skills post-implantation, especially when combined with lipreading. One of the challenges that remain with these implants is that hearing and speech understanding skills after implantation show a wide range of variation across individual implant users. Factors such as duration and cause of hearing loss, how the implant is situated in the cochlea, the overall health of the cochlear nerve, but also individual capabilities of re-learning are considered to contribute to this variation, yet no certain predictive factors are known. In children with severe to profound hearing loss, implants have shown to positively contribute to spoken language development.Despite providing the ability for hearing and oral speech communication to children and adults with severe to profound hearing loss, there is also controversy around the devices. Much of the strongest objection to cochlear implants has come from the Deaf community. For some in the Deaf community, cochlear implants are an affront to their culture, which as some view it, is a minority threatened by the hearing majority.

Deaf culture

Deaf culture is the set of social beliefs, behaviors, art, literary traditions, history, values, and shared institutions of communities that are influenced by deafness and which use sign languages as the main means of communication. When used as a cultural label especially within the culture, the word deaf is often written with a capital D and referred to as "big D Deaf" in speech and sign. When used as a label for the audiological condition, it is written with a lower case d. Carl G. Croneberg coined the term of "Deaf Culture" and he was the first to discuss analogies between Deaf and hearing cultures in his appendices C/D of the 1965 Dictionary of American Sign Language.Members of the Deaf community tend to view deafness as a difference in human experience rather than a disability or disease. Many members take pride in their Deaf identity. Deaf people, in the sense of a community or culture, can then be seen as a minority group, and therefore some who are a part of this community may feel misunderstood by those who don't know sign language. Another struggle that the Deaf community often faces is that educational institutions usually consist primarily of hearing people. Additionally, hearing family members may need to learn sign language in order for the deaf person to feel included and supported. Unlike some other cultures, a deaf person may join the community later in life, rather than needing to be born into it.

There are several perspectives on deaf people and Deaf culture that shape their treatment and role in society. From a medical standpoint, many encourage Deaf children to undergo surgery. Especially in the past, the medical perspective discouraged the use of sign language because they believed it would distract from development of auditory and speech skills. From a social standpoint, Deaf individuals are welcomed to participate in society in the same manner as any other individual. This view discourages the idea that those who are deaf or hard-of-hearing are sick and in need of a cure. The social view also encourages making accommodations for deaf people so that they can fully participate in society. Such accommodations include the use of interpreters or improved closed captioning systems. Many feel, however, that the social view fails to recognize the unique qualities of Deaf people and Deaf culture. They believe that this perspective asks Deaf people to fit and find their own way in a predominantly hearing society, instead of recognizing their own abilities and culture. Another perspective is referred to as the cultural-linguistic view. Supporters of Deaf Culture state that this perspective appropriately recognizes Deaf people as a minority culture in the world with their own language and social norms. This standpoint is believed to promote Deaf people's right to collective space within society to pass on their language and culture to future generations.

Being involved in the Deaf community and culturally identifying as Deaf has been shown to significantly contribute to positive self-esteem in Deaf individuals. The community can provide support, easy social interaction, and "refuge from the grinding frustrations of the hearing world." Conversely, Deaf individuals who are not a part of the Deaf community may not have the same support in the hearing world, resulting in lower self-esteem. Stereotypes, lack of knowledge, and negative attitudes about Deafness cause widespread discrimination. This could lead to a lower education and economic status for deaf people.

The community may include hearing family members of deaf people and sign-language interpreters who identify with Deaf culture. It does not automatically include all people who are deaf or hard-of-hearing. As educator and American Sign Language interpreter Anna Mindess writes, "it is not the extent of hearing loss that defines a member of the deaf community but the individual's own sense of identity and resultant actions." As with all social groups that a person chooses to belong to, a person is a member of the Deaf community if he/she "identifies him/herself as a member of the Deaf community, and other members accept that person as a part of the community."Deaf culture is recognized under Article 30, Paragraph 4 of the United Nations Convention on the Rights of Persons with Disabilities, which states that "Persons with disabilities shall be entitled, on an equal basis with others, to recognition and support of their specific cultural and linguistic identity, including sign languages and deaf culture."


The ear is the organ of hearing and, in mammals, balance. 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 ears of vertebrates are placed somewhat symmetrically on either side of the head, an arrangement that aids sound localisation.

The ear develops from the first pharyngeal pouch and six small swellings that develop in the early embryo called otic placodes, which are derived from ectoderm.

The ear may be affected by disease, including infection and traumatic damage. Diseases of the ear may lead to hearing loss, tinnitus and balance disorders such as vertigo, although many of these conditions may also be affected by damage to the brain or neural pathways leading from the ear.

The ear has been adorned by earrings and other jewelry in numerous cultures for thousands of years, and has been subjected to surgical and cosmetic alterations.


Headphones (or head-phones in the early days of telephony and radio) are a pair of small loudspeaker drivers worn on or around the head over a user's ears. They are electroacoustic transducers, which convert an electrical signal to a corresponding sound. Headphones let a single user listen to an audio source privately, in contrast to a loudspeaker, which emits sound into the open air for anyone nearby to hear. Headphones are also known as earspeakers, earphones or, colloquially, cans. Circumaural ('around the ear') and supra-aural ('over the ear') headphones use a band over the top of the head to hold the speakers in place. The other type, known as earbuds or earpieces consist of individual units that plug into the user's ear canal. In the context of telecommunication, a headset is a combination of headphone and microphone. Headphones connect to a signal source such as an audio amplifier, radio, CD player, portable media player, mobile phone, video game console, or electronic musical instrument, either directly using a cord, or using wireless technology such as Bluetooth, DECT or FM radio. The first headphones were developed in the late 19th century for use by telephone operators, to keep their hands free. Initially the audio quality was mediocre and a step forward was the invention of high fidelity headphones.Headphones are made in a range of different audio reproduction quality capabilities. Headsets designed for telephone use typically cannot reproduce sound with the high fidelity of expensive units designed for music listening by audiophiles. Headphones that use cables typically have either a 1/4 inch (6.35mm) or 1/8 inch (3.5mm) phone jack for plugging the headphones into the audio source. Some stereo earbuds are wireless, using Bluetooth connectivity to transmit the audio signal by radio waves from source devices like cellphones and digital players. Due to the spread of wireless devices in recent years headphones are increasingly used by people in public places such as sidewalks, grocery stores, and public transit. Headphones are also used by people in various professional contexts, such as audio engineers mixing sound for live concerts or sound recordings and DJs, who use headphones to cue up the next song without the audience hearing, aircraft pilots and call center employees. The latter two types of employees use headphones with an integrated microphone.

Hearing aid

A hearing aid is a device designed to improve hearing by making sound audible to a person with hearing loss. Hearing aids are classified as medical devices in most countries, and regulated by the respective regulations. Small audio amplifiers such as PSAPs or other plain sound reinforcing systems cannot be sold as "hearing aids".

Early devices, such as ear trumpets or ear horns, were passive amplification cones designed to gather sound energy and direct it into the ear canal. Modern devices are computerised electroacoustic systems that transform environmental sound to make it audible, according to audiometrical and cognitive rules. Modern devices also utilize sophisticated digital signal processing to try and improve speech intelligibility and comfort for the user. Such signal processing includes feedback management, wide dynamic range compression, directionality, frequency lowering, and noise reduction.

Modern hearing aids require configuration to match the hearing loss, physical features, and lifestyle of the wearer. The hearing aid is fit to the most recent audiogram and is programmed by frequency. This process is called "fitting" and is performed by a Doctor of Audiology, also called an audiologist. The amount of benefit a hearing aid delivers depends in large part on the quality of its fitting. Almost all hearing aids in use in the US are digital hearing aids. Devices similar to hearing aids include the osseointegrated auditory prosthesis (formerly called the bone-anchored hearing aid) and cochlear implant.

Hearing loss

Hearing loss, also known as hearing impairment, is a partial or total inability to hear. A deaf person has little to no hearing. Hearing loss may occur in one or both ears. In children, hearing problems can affect the ability to learn spoken language and in adults it can create difficulties with social interaction and at work. In some people, particularly older people, hearing loss can result in loneliness. Hearing loss can be temporary or permanent.

Hearing loss may be caused by a number of factors, including: genetics, ageing, exposure to noise, some infections, birth complications, trauma to the ear, and certain medications or toxins. A common condition that results in hearing loss is chronic ear infections. Certain infections during pregnancy, such as cytomegalovirus, syphilis and rubella, may also cause hearing loss in the child. Hearing loss is diagnosed when hearing testing finds that a person is unable to hear 25 decibels in at least one ear. Testing for poor hearing is recommended for all newborns. Hearing loss can be categorized as mild (25 to 40 dB), moderate (41 to 55 dB), moderate-severe (56 to 70 dB), severe (71 to 90 dB), or profound (greater than 90 dB). There are three main types of hearing loss: conductive hearing loss, sensorineural hearing loss, and mixed hearing loss.About half of hearing loss globally is preventable through public health measures. Such practices include immunization, proper care around pregnancy, avoiding loud noise, and avoiding certain medications. The World Health Organization recommends that young people limit the use of personal audio players to an hour a day in an effort to limit exposure to noise. Early identification and support are particularly important in children. For many hearing aids, sign language, cochlear implants and subtitles are useful. Lip reading is another useful skill some develop. Access to hearing aids, however, is limited in many areas of the world.As of 2013 hearing loss affects about 1.1 billion people to some degree. It causes disability in 5% (360 to 538 million) and moderate to severe disability in 124 million people. Of those with moderate to severe disability 108 million live in low and middle income countries. Of those with hearing loss, it began during childhood for 65 million. Those who use sign language and are members of Deaf culture see themselves as having a difference rather than an illness. Most members of Deaf culture oppose attempts to cure deafness and some within this community view cochlear implants with concern as they have the potential to eliminate their culture. The term hearing impairment is often viewed negatively as it emphasises what people cannot do.

Hearing range

Hearing range describes the range of frequencies 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.

Several animal species are able to hear frequencies well beyond the human hearing range. Some dolphins and bats, for example, can hear frequencies up to 100,000 Hz. Elephants can hear sounds at 14–16 Hz, while some whales can hear infrasonic sounds as low as 7 Hz (in water).

Ludwig van Beethoven

Ludwig van Beethoven ( (listen); German: [ˈluːtvɪç fan ˈbeːthoːfn̩] (listen); baptised 17 December 1770 – 26 March 1827) was a German composer and pianist. A crucial figure in the transition between the Classical and Romantic eras in classical music, he remains one of the most recognised and influential of all composers. His best-known compositions include 9 symphonies; 5 piano concertos; 1 violin concerto; 32 piano sonatas; 16 string quartets; a mass, the Missa solemnis; and an opera, Fidelio. His career as a composer is conventionally divided into early, middle, and late periods; the "early" period is typically seen to last until 1802, the "middle" period from 1802 to 1812, and the "late" period from 1812 to his death in 1827.

Beethoven was born in Bonn, then the capital of the Electorate of Cologne and part of the Holy Roman Empire. He displayed his musical talents at an early age and was taught by his father Johann van Beethoven and composer and conductor Christian Gottlob Neefe. At the age of 21 he moved to Vienna, where he began studying composition with Joseph Haydn and gained a reputation as a virtuoso pianist. He lived in Vienna until his death. By his late 20s his hearing began to deteriorate and by the last decade of his life he was almost completely deaf. In 1811 he gave up conducting and performing in public but continued to compose; many of his most admired works come from these last 15 years of his life, commonly known as his "late" period.

Ménière's disease

Ménière's disease (MD) is a disorder of the inner ear that is characterized by episodes of feeling like the world is spinning (vertigo), ringing in the ears (tinnitus), hearing loss, and a fullness in the ear. Typically only one ear is affected, at least initially; however, over time both ears may become involved. Episodes generally last from 20 minutes to a few hours. The time between episodes varies. Over time the hearing loss and ringing in the ears may become constant.The cause of Ménière's disease is unclear but likely involves both genetic and environmental factors. A number of theories exist for why it occurs including constrictions in blood vessels, viral infections, and autoimmune reactions. About 10% of cases run in families. Symptoms are believed to occur as the result of increased fluid build up in the labyrinth of the inner ear. Diagnosis is based on the symptoms and frequently a hearing test. Other conditions that may produce similar symptoms include vestibular migraine and transient ischemic attack.There is no known cure. Attacks are often treated with medications to help with the nausea and anxiety. Measures to prevent attacks are overall poorly supported by the evidence. A low salt diet, diuretics, and corticosteroids may be tried. Physical therapy may help with balance and counselling may help with anxiety. Injections into the ear or surgery may also be tried if other measures are not effective but are associated with risks. The use of tympanostomy tubes, while popular, is not supported.Ménière's disease was first identified in the early 1800s by Prosper Ménière. It affects between 0.3 and 1.9 per 1,000 people. It most often starts in people 40 to 60 years old. Females are more commonly affected than males. After 5 to 15 years of symptoms, the episodes of the world spinning generally stop and the person is left with mild loss of balance, moderately poor hearing in the affected ear, and ringing in their ear.


Noise is unwanted sound judged to be unpleasant, loud or disruptive to hearing. From a physics standpoint, noise is indistinguishable from sound, as both are vibrations through a medium, such as air or water. The difference arises when the brain receives and perceives a sound.Acoustic noise is any sound in the acoustic domain, either deliberate (e.g., music or speech) or unintended. In contrast, noise in electronics may not be audible to the human ear and may require instruments for detection.In audio engineering, noise can refer to the unwanted residual electronic noise signal that gives rise to acoustic noise heard as a hiss. This signal noise is commonly measured using A-weighting or ITU-R 468 weighting.In experimental sciences, noise can refer to any random fluctuations of data that hinders perception of a signal.

Noise pollution

Noise pollution, also known as environmental noise or sound pollution, is the propagation of noise with harmful impact on the activity of human or animal life. The source of outdoor noise worldwide is mainly caused by machines, transport and propagation systems. Poor urban planning may give rise to noise pollution, side-by-side industrial and residential buildings can result in noise pollution in the residential areas. Some of the main sources of noise in residential areas include loud music, transportation noise, lawn care maintenance, nearby construction, or young people yelling (sports games). Noise pollution associated with household electricity generators is an emerging environmental degradation in many developing nations. The average noise level of 97.60 dB obtained exceeded the WHO value of 50 dB allowed for residential areas. Research suggests that noise pollution is the highest in low-income and racial minority neighborhoods. Documented problems associated with urban environment noise go back as far as ancient Rome.High noise levels can contribute to cardiovascular effects in humans and an increased incidence of coronary artery disease. In animals, noise can increase the risk of death by altering predator or prey detection and avoidance, interfere with reproduction and navigation, and contribute to permanent hearing loss. While the elderly may have cardiac problems due to noise, according to the World Health Organization, children are especially vulnerable to noise, and the effects that noise has on children may be permanent. Noise poses a serious threat to a child’s physical and psychological health, and may negatively interfere with a child's learning and behavior.

Otitis media

Otitis media is a group of inflammatory diseases of the middle ear. The two main types are acute otitis media (AOM) and otitis media with effusion (OME). AOM is an infection of rapid onset that usually presents with ear pain. In young children this may result in pulling at the ear, increased crying, and poor sleep. Decreased eating and a fever may also be present. OME is typically not associated with symptoms. Occasionally a feeling of fullness is described. It is defined as the presence of non-infectious fluid in the middle ear for more than three months. Chronic suppurative otitis media (CSOM) is middle ear inflammation of greater than two weeks that results in episodes of discharge from the ear. It may be a complication of acute otitis media. Pain is rarely present. All three may be associated with hearing loss. The hearing loss in OME, due to its chronic nature, may affect a child's ability to learn.The cause of AOM is related to childhood anatomy and immune function. Either bacteria or viruses may be involved. Risk factors include exposure to smoke, use of pacifiers, and attending daycare. It occurs more commonly among Indigenous peoples and those who have Down syndrome. OME frequently occurs following AOM and may be related to viral upper respiratory infections, irritants such as smoke, or allergies. Looking at the eardrum is important for making the correct diagnosis. Signs of AOM include bulging or a lack of movement of the tympanic membrane from a puff of air. New discharge not related to otitis externa also indicates the diagnosis.A number of measures decrease the risk of otitis media including pneumococcal and influenza vaccination, breastfeeding, and avoiding tobacco smoke. The use of pain medications for AOM is important. This may include paracetamol (acetaminophen), ibuprofen, benzocaine ear drops, or opioids. In AOM, antibiotics may speed recovery but may result in side effects. Antibiotics are often recommended in those with severe disease or under two years old. In those with less severe disease they may only be recommended in those who do not improve after two or three days. The initial antibiotic of choice is typically amoxicillin. In those with frequent infections tympanostomy tubes may decrease recurrence. In children with otitis media with effusion antibiotics may increase resolution of symptoms, but may cause diarrhoea, vomiting and skin rash.Worldwide AOM affects about 11% of people a year (about 325 to 710 million cases). Half the cases involve children less than five years of age and it is more common among males. Of those affected about 4.8% or 31 million develop chronic suppurative otitis media. Before the age of ten OME affects about 80% of children at some point. Otitis media resulted in 3,200 deaths in 2015 – down from 4,900 deaths in 1990.

Sensorineural hearing loss

Sensorineural hearing loss (SNHL) is a type of hearing loss, or deafness, in which the root cause lies in the inner ear or sensory organ (cochlea and associated structures) or the vestibulocochlear nerve (cranial nerve VIII). SNHL accounts for about 90% of reported hearing loss. SNHL is generally 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.

Sensory hearing loss often occurs as a consequence of damaged or deficient cochlear hair cells. Hair cells may be abnormal at birth, or damaged during the lifetime of an individual. There are both external causes of damage, including noise trauma, infection, and ototoxic drugs, as well as intrinsic causes, including genetic mutations. A common cause or exacerbating factor in sensory hearing loss is prolonged exposure to environmental noise, for example, being in a loud workplace without wearing protection, using headphones at high volume for a long period or being exposed to very loud recreational noise such as in clubs or concerts. Exposure to a single very loud noise such as a bomb blast can cause noise-induced hearing loss.

Neural, or "retrocochlear", hearing loss occurs because of damage to the cochlear nerve (CVIII). This damage may affect the initiation of the nerve impulse in the cochlear nerve or the transmission of the nerve impulse along the nerve into the brainstem.

Most cases of SNHL present with a gradual deterioration of hearing thresholds occurring over years to decades. In some, the loss may eventually affect large portions of the frequency range. It may be accompanied by other symptoms such as ringing in the ears (tinnitus) and dizziness or lightheadedness (vertigo). The most common kind of sensorineural hearing loss is age-related (presbycusis), followed by noise-induced hearing loss (NIHL).

Frequent symptoms of SNHL are loss of acuity in distinguishing foreground voices against noisy backgrounds, difficulty understanding on the telephone, some kinds of sounds seeming excessively loud or shrill, difficulty understanding some parts of speech (fricatives and sibilants), loss of directionality of sound (especially with high frequency sounds), perception that people mumble when speaking, and difficulty understanding speech. Similar symptoms are also associated with other kinds of hearing loss; audiometry or other diagnostic tests are necessary to distinguish sensorineural hearing loss.

Identification of sensorineural hearing loss is usually made by performing a pure tone audiometry (an audiogram) in which bone conduction thresholds are measured. Tympanometry and speech audiometry may be helpful. Testing is performed by an audiologist.

There is no proven or recommended treatment or cure for SNHL; management of hearing loss is usually by hearing strategies and hearing aids. In cases of profound or total deafness, a cochlear implant is a specialised hearing aid which may restore a functional level of hearing. SNHL is at least partially preventable by avoiding environmental noise, ototoxic chemicals and drugs, and head trauma, and treating or inoculating against certain triggering diseases and conditions like meningitis.


In physics, sound is a vibration that typically propagates as an audible wave of pressure, through a transmission medium such as a gas, liquid or solid.

In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Humans can only hear sound waves as distinct pitches when the frequency lies between about 20 Hz and 20 kHz. Sound waves above 20 kHz are known as ultrasound and is not perceptible by humans. Sound waves below 20 Hz are known as infrasound. Different animal species have varying hearing ranges.


Tinnitus is the hearing of sound when no external sound is present. While often described as a ringing, it may also sound like a clicking, hiss or roaring. Rarely, unclear voices or music are heard. The sound may be soft or loud, low pitched or high pitched and appear to be coming from one ear or both. Most of the time, it comes on gradually. In some people, the sound causes depression or anxiety and can interfere with concentration.Tinnitus is not a disease but a symptom that can result from a number of underlying causes. One of the most common causes is noise-induced hearing loss. Other causes include ear infections, disease of the heart or blood vessels, Ménière's disease, brain tumors, emotional stress, exposure to certain medications, a previous head injury, and earwax. It is more common in those with depression.The diagnosis of tinnitus is usually based on the person's description. A number of questionnaires exist that may help to assess how much tinnitus is interfering with a person's life. The diagnosis is commonly supported by an audiogram and a neurological examination. If certain problems are found, medical imaging, such as with MRI, may be performed. Other tests are suitable when tinnitus occurs with the same rhythm as the heartbeat. Rarely, the sound may be heard by someone else using a stethoscope, in which case it is known as objective tinnitus. Spontaneous otoacoustic emissions, which are sounds produced normally by the inner ear, may also occasionally result in tinnitus.Prevention involves avoiding loud noise. If there is an underlying cause, treating it may lead to improvements. Otherwise, typically, management involves talk therapy. Sound generators or hearing aids may help some. As of 2013, there were no effective medications. It is common, affecting about 10–15% of people. Most, however, tolerate it well, and it is a significant problem in only 1–2% of people. The word tinnitus is from the Latin tinnīre which means "to ring".

United States congressional hearing

A United States congressional hearing is the principal formal method by which United States congressional committees collect and analyze information in the early stages of legislative policymaking.

Whether confirmation hearings (a procedure unique to the Senate), legislative, oversight, investigative, or a combination of these, all hearings share common elements of preparation and conduct. Hearings usually include oral testimony from witnesses and questioning of the witnesses by members of Congress. George B. Galloway termed congressional hearings a goldmine of information for all the public problems of the United States. A leading authority on U.S. government publications has referred to the published hearings as "the most important publications originating within Congress." The Senate Library in a similar vein noted "Hearings are among the most important publications originating in Congress." Hearings were not published generally until the latter part of the 19th century, except some early hearings (generally of special investigative committees) were published in the series that are part of the Serial Set. Published hearings did not become available for purchase from the United States Government Printing Office until 1924 and were not distributed to depository libraries until 1938. Unlike the documents and reports that are compiled in the Serial Set "hearings do not constitute a real series" although in the modern era a trend toward uniformity of numbering has resulted in all Senate hearings and prints for each Congressional Session (commencing with the 98th Congress in 1983) being assigned a unique numerical designation (in the style of what one scholar dubbed a "combination code") published on the cover and title page (e.g. S. HRG. 110-113; S. PRT. 110-13). A growing number of House Committees are assigning numerical or alphabetical designations for their publications (e.g. 110-35, 110-AA).

The Law Library of Congress in a collaborative pilot project with Google is undertaking the digitizing of the Library's entire collection of printed hearings (constituting approximately 75,000 volumes). As of 2010 three collections (on the decennial Census, FOIA and Immigration) have been selectively compiled as a test. It is hoped the project will eventually provide full-text access of the entire collection which will be posted online by Google and the Library. ProQuest offers subscriptions to a database of digitized hearings (published and unpublished) covering 1824 to the present.

Special senses
Touch and position
Anatomy of hearing and balance
Outer ear
Middle ear
Inner ear/
(membranous labyrinth,
bony labyrinth)

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