Otoacoustic emission

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.

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 "cubic" distortion tone, most commonly used for hearing screening), because they produce the most robust emission, and

Otoacoustic emissions also assist in differential diagnosis of cochlear and higher level hearing losses (e.g., auditory neuropathy).

[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.

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.

[16] In 2009, Stephen Beeby of the University of Southampton led research into utilizing otoacoustic emissions for biometric identification.

[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] High-end personalized headphone products (e.g., Nuraphone) are being designed to measure OAEs and determine the listener’s sensitivity to different acoustic frequencies.

[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.