Otoacoustic Emissions is used to test inner ear function.
A soft probe that contains a speaker and microphone is placed at the opening of the ear canal. Sounds are sent from the speaker and travel through the middle ear to stimulate the outer hair cells of the inner ear. The hair cells generate their own sound or sometimes called an "echo" which travels back through the middle ear and are detected by the microphone in the probe ear canal.
This test can be used to assess the hearing of individuals of all ages, including newborns.