Otoacoustic emission

An otoacoustic emission (OAE) is a sound which is generated from within the inner ear. Sound' is Vibration transmitted through a Solid, Liquid, or Gas; particularly sound means those vibrations composed of Frequencies The inner Ear is the bony labyrinth, a system of passages comprising two main functional parts the organ of hearing or Cochlea Having been predicted by Thomas Gold in 1948, their existence was first demonstrated experimentally by David Kemp in 1978^[1] and they have since been shown to arise by a number of different cellular mechanisms within the inner ear. Thomas Gold ( May 22, 1920 &ndash June 22, 2004) was an Austrian born Astrophysicist, a professor of Astronomy Year 1948 ( MCMXLVIII) was a Leap year starting on Thursday (link will display the 1948 calendar of the Gregorian calendar. David Kemp is a Professor working at the UCL Ear Institute who discovered the phenomenon of Otoacoustic emission in July 1978 while working at the Year 1978 ( MCMLXXVIII) was a Common year starting on Sunday (link displays the 1978 Gregorian calendar) The inner Ear is the bony labyrinth, a system of passages comprising two main functional parts the organ of hearing or Cochlea Numerous 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. Broadly speaking, there are two types of otoacoustic emissions: Spontaneous Otoacoustic Emissions (SOAEs) and Evoked Otoacoustic Emissions (EOAEs). As their names suggest, SOAEs arise spontaneously and EOAEs require an evoking stimulus.

1 Relations
2 Evoking OAE's
3 Clinical Importance of OAE's
4 References
5 See also

Relations

OAE's are considered to be related to the amplification function of the cochlea. The cochlea is the auditory portion of the Inner ear. Its core component is the Organ of Corti, the sensory organ of hearing, which is distributed along 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. The outer hair cells make only token projections via afferent fibers to the central nervous system. However, they receive extensive efferent innervation, whose activation decreases cochlear sensitivity and frequency discrimination.

Evoking OAE's

OAEs are currently evoked using two different methodologies. 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 or 65 for both) and ratio ( $f 1 : f 2$ ). The evoked responses from these stimuli occur at frequencies ( $f d p$ ) mathematically related to the primary frequencies, with the two most prominent being $f d p = 2 f 1 - f 2$ (the "cubic" distortion tone, most commonly used for hearing screening) and $f d p = f 2 - f 1$ (the "quadratic" distortion tone, or simple difference tone). A combination tone, also called a sum tone or a difference tone, can be any of at least three similar Psychoacoustic phenomena

Clinical Importance of OAE's

Otoacoustic emissions are clinically important because they are the basis of a simple, non-invasive, test for hearing defects in newborn babies and in children who are too young to cooperate in conventional hearing tests. Many western countries now have national programmes for the universal hearing screening of newborn babies. 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).

References

^ Kemp DT. Stimulated acoustic emissions from within the human auditory system. J Acoust Soc Am. 1978;64:1386–1391

Contents

Relations

Evoking OAE's

Clinical Importance of OAE's

References

See also