Hearing a Love Call: What Digital Hearing Aids and Frogs Have in Common

Hearing a Love Call: What Digital Hearing Aids and Frogs Have in Common Digital hearing aids have come a long way in reducing the input from background noise for persons with hearing loss. In fact the Torrent frogs hearing system is similar to the noise reduction technologies being used in todays intelligent hearing aids. 2008 1103 Hearing a Love Call: What Digital Hearing Aids and Frogs Have in Common

Guy walks into a bar. The bartender says, “Hey, you know you got two Chinese torrent frogs in your ears?” The patron looks at the bartender and says, “Oh, these aren’t frogs. They’re my hearing aids.”

(Sound effects: crickets, lone wolf in the distance)

You are saying to yourself “Huh? What’s a Chinese Torrent frog?” I know, not too funny; however, it would be a knee-slapper with the group of researchers at University of Illinois who recently discovered that the male Chinese Torrent frog is able to block out background noise in their environment in order to localize (pinpoint) the direction of an ultrasonic love call from a female torrent frog with uncanny accuracy. (Ribbit. Ribbit.)

And now you’re asking, what does that have to do with hearing aids? Well today’s advanced digital hearing aids offer this same advantage to humans with hearing loss – reduce background noise in order to hear their love calls.

Ultra-Sonic Love Calls

The Torrent frog is known to be the only amphibian that can make long-distant, ultra-sonic calls to its froggy friends during mating season. These ultrasonic calls are well out of the range humans are able to hear. In fact, only a few other animals – bats and dolphins, for example – have this remarkable ability to produce and hear these sounds.


Chinese Torrent Frog

Chinese Torrent Frog (Photo courtesy Albert Feng, UIUC

The Torrent frog has concave ears (they dip in to the side of the frog’s head), which makes it a one-of-a-kind star in the frog world. But more exciting to researchers is the way this unusual amphibian can actually block out certain pitches (specifically low pitch background noise) and tune them back in as needed, simply by closing and opening its ears.

Albert Feng, co-author of the study at the University of Illinois at Urbana-Champaign told the National Geographic, “This was contrary to everything that we know about [the frog’s] auditory system.” Feng and his team of collaborators believe that the torrent frog, which lives near rushing streams and noisy waterfalls, has developed the ability to block out background noise so the critter can hear ultrasonic calls from potential mates and rivals.

Further study reveals that when the torrent frogs actively open and close their ears, they in turn close the Eustachian tube – the narrow canal that connects the ears and mouth (that’s why, when you yawn, your ears “pop” when taking off in an airplane). With the Eustachian tubes closed, the frogs’ ability to hear high-pitched, ultra-sonic signals improves significantly because the inputs from low pitch sounds (those rushing waterfalls) are reduced.

More Studies from the Proceedings of the National Academy of Sciences

James Saunders is an auditory expert out of the University of Pennsylvania who has studied the torrent frogs’ unique ability to tune out frequencies. “This mechanism,” Saunders stated, “is truly unique within the animal kingdom.”

However, the ability to hear select frequencies isn’t unique for humans. For example, when the violins play, you hear them over the rest of the orchestra – your brain automatically tunes into the higher frequencies produced by the violins.

Saunders points out that the ability to select frequencies in humans is actually a “trick of the mind” involving hearing centers that home in on certain sounds coming from a specific direction – in this case, the front row of the string section.

On the other hand, the Chinese Torrent frog actually tunes out frequencies – physically tunes them out by closing their ears to focus on the ultra-sonic sounds emitted by an amphibious mate or the sounds of potential Torrent frog intruders poaching in another frog’s territory.

Hearing Aids and Background Noise

Although humans’ Eustachian tubes have the ability to close, it is not something we do purposely. Pressure changes due to altitude or inflammation from a head cold are the typical causes of our tubes closing off. And contrary to the torrent frog, when they are closed we experience reduced hearing, not improved.

As the researchers reported humans handle background noise naturally with our advanced auditory processing abilities. When in background noise our brains naturally allow us to focus on the speech (high pitch) we want to hear while tune out the background noise (low pitch). However when someone has hearing loss, this natural ability to block out the background noise is often diminished.

So what is the solution for persons with hearing loss having difficulty hearing in background noise? Hearing aids. And no, they do not amplify everything like they used to (those were your great grandpa’s hearing aids).

Digital hearing aids have come a long way in reducing the input from background noise for persons with hearing loss. In fact the Torrent frog's hearing system is similar to the noise reduction technologies being used in today’s "intelligent" hearing aids.

Most digital hearing aids currently on the market offer some level of noise reduction technology that spatially separate sounds, and then processes the sound the way that human brains do. The end result is these intelligent hearing aids boost sound signals of interest, such as desired conversation and reduce the background noise.

Going further, these “intelligent” hearing aids can then be programmed specifically for various environments that may have varying levels of background noise. The most advanced digital hearing aids are even capable of automatically adapting to different settings based on the level of noise in their environment. So like the brain used to before hearing loss occurred, the hearing aids now do the adapting for us. Intelligent I’d say.

Tomorrow’s Hearing Aids

The future? You wouldn’t think these intelligent hearing aids could get anymore sophisticated but they will. Just like the Chinese torrent frog has continued to adapt to their environments, hearing aids will too.

The average age of wearers of hearing aids continues to be younger and younger. And with that means noisier listening environments and more demanding wearers. With ongoing research and development, you can bet hearing aid manufacturers will continue to offer more intelligent and sophisticated hearing aids so humans can continue to hear their love calls or whatever it may be they want to hear.

So, go back and read that joke again. Maybe you’ll even chuckle this time. And maybe you won’t, but at least you’ll get it.

Ribbit. Ribbit.

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