Listen Up!

Most of us normally think of ears as soft, squishy microphones, simply detecting sound. But ears can also emit sound. These sounds, called otoacoustic emissions (OAEs), are thought to be a byproduct of a biological amplifier at work in the ear and they can be detected by inserting a sensitive microphone into the ear canal. A rough analogy: You are delivering a wedding toast and you get too close to the speaker with your microphone. Result? You’ll get screechy feedback.

Typically, only healthy ears emit sound, allowing OAEs to be used for clinical applications such as newborn hearing screening. The biophysical principles underlying sound generation are not well understood, however, which limits their potential use.
Professor Christopher Bergevin of York University’s Centre for Vision Research and Department of Physics & Astronomy is studying how other types of ears can be used to better understand how and why our ears emit sound. His recent work, published in the Proceedings of the National Academy of Sciences, focuses on comparing owls and lizards with humans.
“These animals, just like human beings, emit sound from their ears,” says Bergevin. “The fact that measurements are non-invasive is a bonus. We can obtain fantastic physiological data without harming a scale or a feather.”
The study reported OAEs from all three ear types originate from similar biomechanical principles, despite the differences in ear anatomy. “This indicates there’s a common biophysical thread at work in the ears across the species we studied, even though they are very different structurally,” he says.
“Put another way, not only are we learning something about hearing, but the ear also serves as a striking example of a biological system that can motivate new physics.” ■