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Ear Cells Actively Amplify Sound

A study in the journal Public Library of Science ONE reveals that the ear's hair cells act like tiny motors and respond to sound by swaying and driving electrical currents that cause positive feedbacks, which amplify sound. Karen Hopkin reports

[The following is an exact transcript of this podcast.]

Just when you thought you’d heard everything, scientists have found that the reason you can hear everything—including things that are very quiet—is because your ears have tiny tubelike motors that mechanically amplify sounds.

You’ve probably heard that it’s the hair cells in your ears that allow you to hear. These cells sport tufts of spiky hairs that are like little molecular mohawks. When sound waves enter the ear these hairs vibrate, and that motion then gets translated into an electrical message that tells your brain that there’s something worth listening to. But the movement of those hairs is not passive, like tall grass swaying in the breeze. The electrical signals they produce feed back on the system, causing the hairs to tilt even more. It’s that so-called “flexo-electric effect” that basically boosts the audio signal and amplifies the sound, findings published in the April 22nd issue of the journal Public Library of Science ONE.

The scientists behind the study also note that the length of the hairs in different species explains why animals like bats can detect such high frequency sounds. It doesn’t, however, explain why your kids can hear their cell phone vibrate two rooms away, yet they never seem to hear a word you say.

—Karen Hopkin

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