If an audiologist listens close enough, we can hear your ear. It’s true – a healthy human ear produces sound itself and it is called an otoacoustic emission.
We tend to think of our ears as passive collectors of sound, sending signals to the brain. Our ears are much more complex than that. There are hairs in our inner ear (specifically, the outer hair cells) that are part of an efferent system (where the brain sends signals to the ear). The outer hair cells move (they actually elongate or stretch) and when they do, they generate a sound which travels back out of the ear and can be recorded in the ear canal. You can think of it like a muscle – we decide to flex it, it moves and that movement can be measured.
Otoacoustic emissions were first theorized to exist by Thomas Gold in 1948 but it was not until Jack Kemp in 1978 was able to first measure them. The most common clinical application is to excite the ear with a click and then listen for the otoacoustic emission with a microphone placed in the ear canal. The patient does not need to do or say anything.
Otoacoustic emissions are tremendously useful in the field of pediatric audiology as very young children can not tell us what they are hearing. Because it is a quick, reliable test of ear function that does not require a behavioral response, it has been instrumental in the development of Universal Newborn Hearing Screening programs around the world. The first of these programs began in Colorado in the mid-1990s.
When I began practicing as a pediatric audiologist in 2000, the health authority hearing clinic did not have access to a machine to measure otoacoustic emissions. Now, the technology is fundamental to the practice of pediatric audiology. All infants in BC have their hearing screened at birth using this technology and next time I will elaborate on how the BC Early Hearing Program is able to diagnose and help infants with hearing loss.