Otoacoustics

Otoacoustics refers to sounds generated by the inner ear. Specifically, these are low-intensity sounds produced by the cochlea, a part of the inner ear responsible for hearing. These sounds are thought to originate from the mechanical activity of the outer hair cells, which are specialized sensory cells within the cochlea. When these cells are stimulated by incoming sound, they undergo changes in length, acting like tiny amplifiers or generators of sound energy. This amplified energy is then transmitted back through the middle ear and can be detected by a sensitive microphone placed in the ear canal.

The measurement of otoacoustic emissions (OAEs) is a non-invasive diagnostic tool used to assess the function of the outer hair cells and the cochlea. OAEs are broadly categorized into two main types: spontaneous otoacoustic emissions (SOAEs), which occur in the absence of external sound, and evoked otoacoustic emissions (EOAEs), which are produced in response to an external sound stimulus. EOAEs can be further classified based on the nature of the stimulus, such as transient-evoked otoacoustic emissions (TEOAEs) and distortion-product otoacoustic emissions (DPOAEs).

Otoacoustic emissions are routinely used in newborn hearing screening programs because they are sensitive to even minor cochlear dysfunction. Their presence indicates that the outer hair cells are functioning, which is a crucial component of normal hearing. Abnormal or absent OAEs can suggest hearing loss, particularly sensorineural hearing loss, prompting further audiological evaluation. OAEs are also employed in research to understand cochlear mechanics and the effects of noise exposure or ototoxic drugs on hearing.