Chinese Torrent frogs are able to communicate clearly, despite the background of crashing waterfalls.
All species of frogs have their own distinct mating calls, from a deep croak to a tiny ribbit. This makes perfect sense, as only the same species of frogs can mate. However, a single pond can house hundreds of frogs at one time, making a frog’s ability to discern one frogs call from another rather difficult. By studying the way frogs are able to overcome this cocktail party effect — the ability to pick out a specific sound or voice from acoustic clutter — researchers plan to utilise the same technique to better current hearing aid technologies.
The Torrent frog (Odorrana tormota) is the only amphibian that can make long-distant, ultrasonic calls to its frog 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.
Albert Feng, who works at the University of Illinois and is the co-author of the study, told National Geographic “This was contrary to everything that we know about the frog’s auditory system.” The Torrent frog differs from other species in that it has concave ears that it can close and open to block out certain pitches — specifically low pitch — and tune them back in as needed. Feng and his colleagues believe that this amphibian, which lives near rushing streams and noisy waterfalls, has developed the ability to block out background noise so the critter can hear ultra-sonic calls from potential mates and rivals.
Further study revealed that when these creatures actively open and close their ears, they correspondingly close the Eustachian tube — the canal that connects the ears and the mouth. This improves the frog’s ability to hear high-pitched, ultra-sonic signals significantly, since the inputs from low-pitched background sounds are reduced.
Although humans’ Eustachian tubes have the ability to close, it is not something we do purposely. Pressure changes due to altitude (such as your ears popping on a plane) or inflammation are typical causes of our tubes closing off. Further more, contrary to the Torrent frog, when they are closed we experience reduced hearing rather than improved.
Humans usually handle background noise with our advanced auditory processing abilities. Our brains naturally allow us to focus on the speech (high pitch) and tune out background noise (low pitch). However, when someone has hearing loss this natural ability to block out unwanted background noise is diminished, as traditional hearing aids amplify all surrounding sounds.
However, there is hope. 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 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.
“These directional hearing aids are great in situations like crowded parties,” said study co-author Peter Narins, a professor of physiological science at the University of California, in the US. “With an ordinary hearing aid, the user can only turn up the volume of all the sound around him. But with a directional device, he can focus on and amplify the voice of the person next to him.”