Otoacoustic emission

Last updated November 07, 2023

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,^[1] and otoacoustic emissions have since been shown to arise through a number of different cellular and mechanical causes within the inner ear.^[2]^[3] 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.

Mechanism of occurrence

OAEs are considered to be related to the amplification function of the cochlea. In the absence of external stimulation, the activity of the cochlear amplifier increases, leading to the production of sound. Several lines of evidence suggest that, in mammals, outer hair cells are the elements that enhance cochlear sensitivity and frequency selectivity and hence act as the energy sources for amplification.

Types

Spontaneous

Spontaneous otoacoustic emissions (SOAEs) are sounds that are emitted from the ear without external stimulation and are measurable with sensitive microphones in the external ear canal. At least one SOAE can be detected in approximately 35–50% of the population. The sounds are frequency-stable between 500 Hz and 4,500 Hz and have unstable volumes between -30 dB SPL and +10 dB SPL. The majority of those with SOAEs are unaware of them, however 1–9% perceive a SOAE as an annoying tinnitus.^[4] It has been suggested that "The Hum" phenomena are SOAEs.

Evoked

Evoked otoacoustic emissions are currently evoked using three different methodologies.

Stimulus-frequency OAEs (SFOAEs) are measured during the application of a pure-tone stimulus and are detected by the vectorial difference between the stimulus waveform and the recorded waveform (which consists of the sum of the stimulus and the OAE).
Transient-evoked OAEs (TEOAEs or TrOAEs) are evoked using a click (broad frequency range) or toneburst (brief duration pure tone) stimulus. The evoked response from a click covers the frequency range up to around 4 kHz, while a toneburst will elicit a response from the region that has the same frequency as the pure tone.
Distortion-product OAEs (DPOAEs) are evoked using a pair of primary tones $f_{1}$ and $f_{2}$ with particular intensity (usually either 65–55 dB SPL or 65 for both) and ratio ( $f_{1}{\mbox{ }}:{\mbox{ }}f_{2}$ ).

The evoked responses from these stimuli occur at frequencies ( $f_{dp}$ ) mathematically related to the primary frequencies, with the two most prominent being $f_{dp}=2f_{1}-f_{2}$ (the "cubic" distortion tone, most commonly used for hearing screening), because they produce the most robust emission, and $f_{dp}=f_{2}-f_{1}$ (the "quadratic" distortion tone, or simple difference tone).^[5]^[6]

Clinical importance

Otoacoustic emissions are clinically important because they are the basis of a simple, non-invasive test for cochlear hearing loss in newborn babies and in children or adults who are unable or unwilling to cooperate during conventional hearing tests. In addition, the OAEs are highly reliable making it suitable for diagnostic and screening applications.^[7] Many western countries now have national programmes for the universal hearing screening of newborn babies. Newborn hearing screening is state-mandated prior to hospital discharge in the United States. Periodic early childhood hearing screenings programs are also utilizing OAE technology. The Early Childhood Hearing Outreach Initiative at the National Center for Hearing Assessment and Management (NCHAM) at Utah State University has helped hundreds of Early Head Start programs across the United States implement OAE screening and follow-up practices in those early childhood educational settings.^[8]^[9]^[10] The primary screening tool is a test for the presence of a click-evoked OAE. Otoacoustic emissions also assist in differential diagnosis of cochlear and higher level hearing losses (e.g., auditory neuropathy).

The relationships between otoacoustic emissions and tinnitus have been explored. Several studies suggest that in about 6% to 12% of normal-hearing persons with tinnitus and SOAEs, the SOAEs are at least partly responsible for the tinnitus.^[11] Studies have found that some subjects with tinnitus display oscillating or ringing EOAEs, and in these cases, it is hypothesized that the oscillating EOAEs and tinnitus are related to a common underlying pathology rather than the emissions being the source of the tinnitus.^[11]

In conjunction with audiometric testing, OAE testing can be completed to determine changes in the responses. Studies have found that exposure to noise can cause a decline in OAE responses. OAEs are a measurement of the activity of outer hair cells in the cochlea, and noise-induced hearing loss occurs as a result of damage to the outer hair cells in the cochlea.^[12]^[13] Therefore, the damage or loss of some outer hair cells will likely show up on OAEs before showing up on the audiogram.^[12] Studies have shown that for some individuals with normal hearing that have been exposed to excessive sound levels, fewer, reduced, or no OAEs can be present.^[12] This could be an indication of noise-induced hearing loss before it is seen on an audiogram. In one study, a group of subjects with noise exposure was compared to a group of subjects with normal audiograms and a history of noise exposure, as well as a group of military recruits with no history of noise exposure and a normal audiogram.^[14] They found that an increase in severity of the noise-induced hearing loss resulted in OAEs with a smaller range of emissions and reduced amplitude of the emissions. The loss of emissions due to noise exposure was found to occur mostly in higher frequencies, and it was more prominent in the groups that had noise exposure in comparison to the non-exposed group. It was found that OAEs were more sensitive to identifying noise-induced cochlear damage than pure tone audiometry.^[14] In conclusion, the study identified OAEs as a method for helping with detection of the early onset of noise-induced hearing loss.

It has been found that distortion-product otoacoustic emissions (DPOAE's) have provided the most information for detecting hearing loss in high frequencies when compared to transient-evoked otoacoustic emissions (TEOAE).^[15] This is an indication that DPOAE's can help with detecting an early onset of noise-induced hearing loss. A study measuring audiometric thresholds and DPOAEs among individuals in the military showed that there was a decrease in DPOAEs after noise exposure, but did not show a shift in audiometric threshold. This supports OAEs as predicting early signs of noise damage.^[16]

Biometric importance

In 2009, Stephen Beeby of the University of Southampton led research into utilizing otoacoustic emissions for biometric identification. Devices equipped with a microphone could detect these subsonic emissions and potentially identify an individual, thereby providing access to the device, without the need of a traditional password.^[17] It is speculated, however, that colds, medication, trimming one's ear hair, or recording and playing back a signal to the microphone could subvert the identification process.^[18]

Measuring otoacoustic emissions on earphones

High-end personalized headphone products (e.g., Nuraphone) are being designed to measure OAEs and determine the listener’s sensitivity to different acoustic frequencies. This is then used to personalize the audio signal for each listener.^[19]

In 2022, researchers at the University of Washington built a low-cost prototype that can reliably detect otoacoustic emissions using commodity earphones and microphones attached to a smartphone.^[20] The low-cost prototype sends two frequency tones through each of the headphone’s earbuds, detects the distortion-product OAEs generated by the cochlea and recorded via the microphone. Such low-cost technologies may help larger efforts to achieve universal neonatal hearing screening across the world.^[21]

Related Research Articles

Hearing loss is a partial or total inability to hear. Hearing loss may be present at birth or acquired at any time afterwards. Hearing loss may occur in one or both ears. In children, hearing problems can affect the ability to acquire spoken language, and in adults it can create difficulties with social interaction and at work. Hearing loss can be temporary or permanent. Hearing loss related to age usually affects both ears and is due to cochlear hair cell loss. In some people, particularly older people, hearing loss can result in loneliness. Deaf people usually have little to no hearing.

Tinnitus is a variety of sound that is heard when no corresponding external sound is present. Nearly everyone experiences faint "normal tinnitus" in a completely quiet room; but it is of concern only if it is bothersome, interferes with normal hearing, or is associated with other problems. The word tinnitus comes from the Latin tinnire, "to ring". In some people, it interferes with concentration, and can be associated with anxiety and depression.

<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.

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.

Ototoxicity is the property of being toxic to the ear (oto-), specifically the cochlea or auditory nerve and sometimes the vestibular system, for example, as a side effect of a drug. The effects of ototoxicity can be reversible and temporary, or irreversible and permanent. It has been recognized since the 19th century. There are many well-known ototoxic drugs used in clinical situations, and they are prescribed, despite the risk of hearing disorders, for very serious health conditions. Ototoxic drugs include antibiotics, loop diuretics, and platinum-based chemotherapy agents. A number of nonsteroidal anti-inflammatory drugs (NSAIDS) have also been shown to be ototoxic. This can result in sensorineural hearing loss, dysequilibrium, or both. Some environmental and occupational chemicals have also been shown to affect the auditory system and interact with noise.

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 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.

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.

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">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.

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.

Noise-induced hearing loss (NIHL) is a hearing impairment resulting from exposure to loud sound. People may have a loss of perception of a narrow range of frequencies or impaired perception of sound including sensitivity to sound or ringing in the ears. When exposure to hazards such as noise occur at work and is associated with hearing loss, it is referred to as occupational hearing loss.

<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.

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.

Auditory fatigue is defined as a temporary loss of hearing after exposure to sound. This results in a temporary shift of the auditory threshold known as a temporary threshold shift (TTS). The damage can become permanent if sufficient recovery time is not allowed before continued sound exposure. When the hearing loss is rooted from a traumatic occurrence, it may be classified as noise-induced hearing loss, or NIHL.

Acoustic trauma is the sustainment of an injury to the eardrum as a result of a very loud noise. Its scope usually covers loud noises with a short duration, such as an explosion, gunshot or a burst of loud shouting. Quieter sounds that are concentrated in a narrow frequency may also cause damage to specific frequency receptors. The range of severity can vary from pain to hearing loss.

An audiologist, according to the American Academy of Audiology, "is a person who, by virtue of academic degree, clinical training, and license to practice and/or professional credential, is uniquely qualified to provide a comprehensive array of professional services related to the prevention of hearing loss and the audiologic identification, assessment, diagnosis, and treatment of persons with impairment of auditory and vestibular function, and to the prevention of impairments associated with them."

<span class="mw-page-title-main">Diagnosis of hearing loss</span>

Identification of a hearing loss is usually conducted by a general practitioner medical doctor, otolaryngologist, certified and licensed audiologist, school or industrial audiometrist, or other audiometric technician. Diagnosis of the cause of a hearing loss is carried out by a specialist physician or otorhinolaryngologist.

Computational audiology is a branch of audiology that employs techniques from mathematics and computer science to improve clinical treatments and scientific understanding of the auditory system. Computational audiology is closely related to computational medicine, which uses quantitative models to develop improved methods for general disease diagnosis and treatment.

References

↑ Kemp, D. T. (1 January 1978). "Stimulated acoustic emissions from within the human auditory system". The Journal of the Acoustical Society of America. 64 (5): 1386–1391. Bibcode:1978ASAJ...64.1386K. doi:10.1121/1.382104. PMID 744838.
↑ Kujawa, SG; Fallon, M; Skellett, RA; Bobbin, RP (August 1996). "Time-varying alterations in the f2-f1 DPOAE response to continuous primary stimulation. II. Influence of local calcium-dependent mechanisms". Hearing Research. 97 (1–2): 153–64. doi:10.1016/s0378-5955(96)80016-5. PMID 8844195. S2CID 4765615.
↑ Chang, Kay W.; Norton, Susan (1 September 1997). "Efferently mediated changes in the quadratic distortion product (f2−f1)". The Journal of the Acoustical Society of America. 102 (3): 1719. Bibcode:1997ASAJ..102.1719C. doi:10.1121/1.420082.
↑ Penner M. J. (1990). "An estimate of the prevalence of tinnitus caused by spontaneous otoacoustic emissions". Arch Otolaryngol Head Neck Surg. 116 (4): 418–423. doi:10.1001/archotol.1990.01870040040010. PMID 2317322.
↑ Kujawa, SG; Fallon, M; Bobbin, RP (May 1995). "Time-varying alterations in the f2-f1 DPOAE response to continuous primary stimulation. I: Response characterization and contribution of the olivocochlear efferents". Hearing Research. 85 (1–2): 142–54. doi:10.1016/0378-5955(95)00041-2. PMID 7559170. S2CID 4772169.
↑ Bian, L; Chen, S (December 2008). "Comparing the optimal signal conditions for recording cubic and quadratic distortion product otoacoustic emissions". The Journal of the Acoustical Society of America. 124 (6): 3739–50. Bibcode:2008ASAJ..124.3739B. doi:10.1121/1.3001706. PMC 2676628 . PMID 19206801.
↑ Kalaiah M, Lasrado A, Pinto N, Shastri U (2018). "Short term test-retest reliability of contralateral inhibition of distortion product otoacoustic emissions". Journal of Audiology and Otology. 22 (4): 189–196. doi: 10.7874/jao.2018.00038 . PMC 6233937 . PMID 30126264. S2CID 52048509.
↑ Eiserman, W., & Shisler, L. (2010). Identifying Hearing Loss in Young Children: Technology Replaces the Bell. Zero to Three Journal, 30, No.5, 24-28.
↑ Eiserman W.; Hartel D.; Shisler L.; Buhrmann J.; White K.; Foust T. (2008). "Using otoacoustic emissions to screen for hearing loss in early childhood care settings". International Journal of Pediatric Otorhinolaryngology. 72 (4): 475–482. doi:10.1016/j.ijporl.2007.12.006. PMID 18276019.
↑ Eiserman, W., Shisler, L., & Foust, T. (2008). Hearing screening in Early Childcare Settings. The ASHA Leader. November 4, 2008.
1 2 Norton, SJ; et al. (1990), "Tinnitus and otoacoustic emissions: is there a link?", Ear Hear, 11 (2): 159–166, doi:10.1097/00003446-199004000-00011, PMID 2340968, S2CID 45416116.
1 2 3 Robinette, Martin; Glattke, Theodore (2007). Otoacoustic Emissions: Clinical Applications. New York: Thieme Medical Publishers Inc. ISBN 978-1-58890-411-9.
↑ Hall, III, James (2000). Handbook of Otoacoustic Emissions. New York: Thomson Delmar Learning. ISBN 1-56593-873-9.
1 2 Henderson, Don; Prasher, Deepak; Kopke, Richard; Salvi, Richard; Hamernik, Roger (2001). Noise Induced Hearing Loss: Basic Mechanisms, Prevention and Control. London: Noise Research Network Publications. ISBN 1-901747-01-8.
↑ Kemp, D. T (2002-10-01). "Otoacoustic emissions, their origin in cochlear function, and use". British Medical Bulletin. 63 (1): 223–241. doi: 10.1093/bmb/63.1.223 . ISSN 0007-1420. PMID 12324396.
↑ Marshall, Lynne; Miller, Judi A. Lapsley; Heller, Laurie M.; Wolgemuth, Keith S.; Hughes, Linda M.; Smith, Shelley D.; Kopke, Richard D. (2009-02-01). "Detecting incipient inner-ear damage from impulse noise with otoacoustic emissions". The Journal of the Acoustical Society of America. 125 (2): 995–1013. Bibcode:2009ASAJ..125..995M. doi:10.1121/1.3050304. ISSN 0001-4966. PMID 19206875.
↑ Telegraph.co.uk, April 25, 2009, "Ear noise can be used as identification"
↑ IEEE Spectrum Online, April 29, 2009, "Your Ear Noise as Computer Password Archived 2009-05-03 at the Wayback Machine "
↑ HHTM (2017-10-24). "Nura Headphones: Using OAEs to Customize the Listening Experience". Hearing Health & Technology Matters. Retrieved 2022-10-31.
↑ Chan, Justin; Ali, Nada; Najafi, Ali; Meehan, Anna; Mancl, Lisa R.; Gallagher, Emily; Bly, Randall; Gollakota, Shyamnath (2022-10-31). "An off-the-shelf otoacoustic-emission probe for hearing screening via a smartphone". Nature Biomedical Engineering. 6 (11): 1203–1213. doi:10.1038/s41551-022-00947-6. ISSN 2157-846X. PMC 9717525 . PMID 36316369. S2CID 253246239.
↑ Goodman, Shawn S. (2022-10-31). "Affordable hearing screening". Nature Biomedical Engineering. 6 (11): 1199–1200. doi:10.1038/s41551-022-00959-2. ISSN 2157-846X. PMID 36316370. S2CID 253246312.