Otoacoustic emissions

Congenital hearing impairment has adverse effects on speech and language acquisition as well as on emotional and intellectual development. It has been confirmed that these effects are reduced when recognition and intervention in the case of hearing impairment occur before the age of six months. Otoacoustic emissions (OAEs) are vibrations created by contractions of the outer haircells that are located in the cochlea. It is hypothesized that outer- hair cell contraction follows inner hair cell stimulation, thus enhancing the spatial resolution of the cochlea. The identification and recognition of sounds of different frequency is thereby amplified. The outer hair cell contraction generates a vibration within the cochlea that is retrogradely transduced to the middle ear. There, it is transduced by the ossicles to the eardrum, that is brought to vibration. These vibrations create sounds that can be recorded in the ear canal. These sounds are soft, but potentially audible, infrequently amounting to as much as 30 dB SPL. For detection of these OAEs, normal middle ear function is mandatory. OAEs are generated only when the organ of Corti is in normal or near normal condition and their presence, therefore, is indicative of normal middle ear and cochlear function. OAEs may emerge spontaneously, but more commonly follow acoustic stimulation as described above.