German researchers have discovered that humans, like some animals, can also direct their ears toward interesting sounds. The findings could be helpful in the development of new hearing aids.
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The slightest rustle or crackle is enough — in a flash, the ears of dogs or cats point in the direction of the noise. Some species of monkeys can also direct their ears in a targeted manner.
Until now, science assumed that humans have never possessed this ability or lost it completely in the course of evolution. But researchers at the University of Saarland have now presented a study showing that humans do indeed unconsciously point their ears in the direction from which an interesting sound is coming. However, the ear movements are only minimal and practically undetectable.
Pricking up their ears
The muscles around the ear become active as soon as "novel, striking or task-relevant stimuli are perceived," say researchers from the "Systems Neuroscience & Neurotechnology Unit" (SNNU) headed by Prof. Daniel Strauss.
Strauss, a neuroscientist and computer scientist, explains that "the electrical activity of the ear muscles reflects the direction in which a person aims their attention when listening."
Dogs direct their ears specifically in the direction of a striking noiseImage: Getty Images/AFP/D. Sarkar
To detect the minimal movements, the researchers used sensors around the ear to record the electrical activity in the muscles that change the shape of the shell of the ear — the auricle — or move it, according to their report in the journal eLife. In addition, the test subjects were observed on special, high-resolution video recordings.
25 million-year-old 'neural fossil'
According to Strauss, humans have probably retained an orientation system that attempts to control the movement of their auricles. He believes that the newly discovered ability is a kind of "neural fossil" that has persisted in the human brain for about 25 million years.
It remains unclear, however, why this alignment of the ears in the primate chain has been largely lost, said Strauss.
Two types of attention
While the test persons were reading a monotonous text, they were surprised by unfamiliar noises from various lateral positions. In this way, the researchers were able to test the "reflexive attention" that automatically occurs when unexpected noises occur.
Distinguishing important sounds from background noise: Targeted hearing includes reflexive and goal-oriented attentionImage: Colourbox/A. Shupilo
In addition, the test subjects had to listen to a short story read aloud to them from one side while at the same time ignoring a "competing" story from the opposite side. This allowed the testing of "goal-oriented attention," as it occurs, for example, during active listening.
Both test setups showed that the movements of the vestigial muscles in the human ear indicate the direction of the sounds the test subjects are paying attention to.
Depending on the type of stimulus, the researchers recorded minimal, varying, upward movements of the ear or backward movements of the lateral edge of the auricle at varying degrees of intensity.
Basis for more targeted hearing aids?
The findings made by the Saarland research team are interesting not only with regard to the history of evolution or for basic research. They could possibly also be used to develop better hearing aids.
"These could amplify the sounds that the wearer tries to hear while suppressing the sounds that he or she tries to ignore. In this way, the function of the devices would virtually follow the hearing intention of the user," says Prof. Strauss.
New types of hearing aids could specifically amplify sounds and block out background noiseImage: Colourbox
A new type of hearing aid could detect the electrical activity of the ear muscles in milliseconds and thus determine the direction in which the ears are trying to align themselves. A built-in computer could then amplify the directional microphones in a targeted manner and suppress disturbing background noise.
Hearing beyond ears: Animals and their amazing listening techniques
Humans lost some hearing privileges to evolution. We can’t hear frequencies as low as elephants or as high as bats, and we can’t move our ears like cats. However, we learned to enhance our hearing abilities.
Image: picture-alliance/dpa/P. Pleul
Rabbits can rotate their ears 270 degrees
Rabbits direct their ears toward sounds. Ear movement helps them to escape predators, but a rabbit’s ears also tell a lot about behavior. Erect ears mean they’re listening attentively. When one ear is up and one is down, the rabbit is listening passively. Ears resting against the back indicate a relaxed state of mind if ears are touching, but separated ears in the same position are a sign of fear.
Image: picture-alliance/dpa/P. Pleul
Cats and dogs are very attentive
Dogs can hear higher frequencies than humans. That’s why your dog reacts even when nothing seems to be there. Dogs can also differentiate their owner’s footsteps from those of strangers. Cat ears are even more sensitive! Dogs have 18 ear muscles, while cats have 30 and can even rotate them 180 degrees. So, don’t try to sneak up on your cat — it’s pointless.
Image: picture-alliance/dpa/P. Faber
Bats use ultrasonic sound waves to hear
Bats rely on echolocation to navigate during night flights. They send out ultrasonic sound waves from their mouths then the echo bounces back to the bat. Bats use this strategy to determine the size and location of objects and to find food in total darkness. Additionally, bats have 20 muscles to change the shape and direction of their ears to fine-tune their echo reception.
Image: picture-alliance/Mary Evans Picture Library/J. Daniel
The "best hearing in the world" title goes to an earless animal
In the everlasting predator-prey race, the greater wax moths have managed to escape bat predation by evolving ultrasound sensitive ears. They have the highest frequency sensitivity recorded in the animal world and hear 150 times better than humans. They can even hear frequencies 100 hertz higher than bats.
When beetles, crickets, and moths hear ultrasonic waves of their predators they run away or fly in zigzagging or looping patterns. Some crickets and beetles produce clicking sounds to scare the predators away.
Image: picture-alliance/AP Images/J. Schultz
Whales are living submarines
Underwater sonar is based on similar echolocation techniques bats and whales use to navigate at night or in the deep dark ocean. Like submarines, whales can navigate and find food using sound waves and sound reflections. Whistles and clicks produced by whales are thought to provide them with a 3D view of the world and are also important in communication between individuals.
Image: picture-alliance/WILDLIFE/W. Poelzer
Dolphins can hear through their jaw
Dolphins have ears; however, they navigate through the ocean by a mechanism similar to echolocation in bats. They produce sonic pulses from their foreheads that are reflected by the surroundings and then received by sound receptors in their jaws and teeth. Yes, that’s right! Hearing doesn’t necessarily have to be through ears, it can simply refer to information reception.
Image: picture-alliance/WILDLIFE/W. Peolzer
Elephants can sense a thunderstorm!
With their enormous ears, they can hear the sound of the clouds gathering prior to rain. Elephants can pick up infrasound waves — a low frequency humans can’t hear. They can also hear with their feet using nerve endings that detect ground vibrations. Some animals have receptors on parts of their bodies which convey vibrations and sound waves to the nervous system.
Image: picture-alliance/M. Reichelt
Owls are nature’s surveillance camera
Not only do owls have excellent night vision and the ability to rotate their heads 360 degrees, but they also have remarkable hearing. Owls have asymmetrical ears, so when they fly, one ear picks up sounds from above while the other listens to sounds from below. This system working tandem with their night vision means their prey will most definitely get caught.
Image: DW
Some blind people practice navigation like bats
Some blind individuals have learned to use echolocation to "hear" their surroundings. One way they do this is by making clicking sounds with their mouths then listening to reverberations to estimate the size of a room or the distance to a wall or a fence. Some claim to be able to describe a place relying on echolocation alone!
