OAE or otoacoustic emission testing is the recording of sounds that the ear produces itself.
Having been predicted by Thomas Gold in 1948, its existence was first demonstrated experimentally by David Kemp in 1978 and otoacoustic emissions have since been shown to arise through a number of different cellular and mechanical causes within the inner ear. Spontaneous otoacoustic emissions (SOAE)s 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 app. Otoacoustic emissions are acoustic signals generated by the normal inner ear, either in the absence of acoustic stimulation (spontaneous emissions) or in response to acoustic stimulation (acoustically-evoked emissions) or electrical stimulation (electrically-evoked emissions). There are three types of Otoacoustic emission testing: Spontaneous, Transient, and Distortion Product. We will only discuss Distortion Product testing (DPOAE) here. To obtain DPOAE measurements, the audiologist will position an earplug in your outer ear. Broadly speaking, there are two types of otoacoustic emissions: spontaneous otoacoustic emissions (SOAEs), which can occur without external stimulation, and evoked otoacoustic emissions (EOAEs), which require an evoking stimulus. Spontaneous otoacoustic emissions (SOAE)s 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 app. OAEs are faint acoustical signals that emit from the outer hair cells located in the cochlea of the inner ear, in response to presented stimuli. This test is a measure of cochlear function; it is not a threshold test such as a hearing test. It measures an acoustic response from the inner ear to an external sound stimulus. This test is ideal as part of a test battery when trying to determine auditory function in infants, small children, and patients who otherwise cannot or do not respond to the behavioral tests typically employed. Otoacoustic Emission Testing The cochlea is the sensory organ for hearing contained in the inner ear. It is housed within the temporal bone which is the hardest bone in the human body. Within the cochlea is a structure called the Organ of Corti. This structure contains the inner and outer hair cells. There are three types of Otoacoustic emission testing: Spontaneous, Transient, and Distortion Product. We will only discuss Distortion Product testing (DPOAE) here. To obtain DPOAE measurements, the audiologist will position an earplug in your outer ear. OAE or otoacoustic emission testing is the recording of sounds that the ear produces itself. Otoacoustic emissions were first reported by Kemp in 1978. They appear to be generated by motile elements in the cochlear outer hair cells (see image above).  What is Otoacoustic Emission Testing (OAE)? The Otoacoustic Emission test is an objective test, which measures hair cell function in the inner ear. An emission is a sound generated within the normal cochlea in response to stimulation. Otoacoustic emissions (OAEs) are sounds given off by the inner ear when the cochlea is stimulated by a sound. When sound stimulates the cochlea, the outer hair cells vibrate.  An otoacoustic emission (OAE) is a sound which is generated from within the inner ear. Spontaneous otoacoustic emissions (SOAE)s 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 app. Rebekah F. Cunningham. An otoacoustic emission (OAE) is a low-level sound emitted by the cochlea either spontaneously or evoked by an auditory stimulus. Specifically, OAEs provide information related to the function of the outer hair cells (OHC) (Stach, 2003). 
https://en.wikipedia.org/wiki/Otoacoustic_emission http://www.audible-difference.com/Articles/otoacoustic_emission_testing.htm https://en.wikipedia.org/wiki/Otoacoustic_emission http://www.ccent.com/webdocuments/OAE-Facts.pdf http://www.audible-difference.com/Articles/otoacoustic_emission_testing.htm http://www.dizziness-and-balance.com/testing/hearing/OAE.htm http://www.hopkinsmedicine.org/hearing/hearing_testing/oae.html http://www.asha.org/public/hearing/Otoacoustic-Emissions/ https://en.wikipedia.org/wiki/Otoacoustic_emission http://www.audiologyonline.com/articles/otoacoustic-emissions-beyond-newborn-hearing-838
what does otoacoustic emissions measure