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Researchers fed bats in helium-rich air to determine how they perceive sounds.



Image of bats in flight

It is now accepted that bats can develop a picture of their environment using echolocation, but we are still figuring out what that means – how bats use the echo of their cry and use it to locate objects.

In a paper published today, the researchers provide evidence that bats are involved in sound alignment, in part because they are born with an innate sense of the speed of sound. How do researchers study this phenomenon? By raising bats in a helium-filled atmosphere, the low-density air increases the speed of sound.

Positioning in the echo

Echolocation is, in principle, relatively simple.Bats make a sound, which bounces off objects in their environment and then returns to the bat̵

7;s ears. For distant objects, the sound takes longer to return to the bat, giving a sense of relative distance.

But bats can use echolocation to identify prey during flight or choose where to land. Because of this, they must have a sense of a certain distance. It’s not enough to know that the branch you want to land on is closer than the back house. You have to know when to initiate all the complex movements that involve sticking to the branches, or you could run into them or try to stop mid-air.

The easiest way to find a certain distance is to know the speed of sound. As a result, the delay between articulation and reflection provides a certain distance. But how do you test if bats have a sense of the speed of sound?

Eran Amichai and Yossi Yovel from Tel Aviv University decided there was an easy way to change the speed of sound. One of the factors that affect the speed of sound is air density. And there’s a simple way to change the air density: obstructed with a gas that’s lighter than air. In this case, the authors chose helium and raised a group of bats in an atmosphere with enough helium to increase the speed of sound by 15 percent.

(Whether bats raised in this kind of environment thought it sounded funny or not, sadly hasn’t been tested.)

The distance measured by the bat.

The faster the speed of the sound means the faster the resonance is reflected back to the bat. This means that those resonating objects are viewed as closer than they are. Therefore, if we can find out how close the bats perceive the object, we can measure our understanding of the velocity of sound.

Fortunately, the type of bat used in these experiments changes the resonance position as it gets closer to the object. So by following the sound the bats make as they get closer to the object, we can understand how close they think they are.

In this experiment, the researchers propagated bats in a distant feeding station, one of which was raised in normal air and the other in helium-rich air. They then changed the atmosphere for both groups. For helium-fed bats, the slower air velocity makes the resonance take longer to arrive and makes the feeding station seem more distant. The opposite is true for bats that are raised in normal air.

It turns out that both groups of bats behave the same. They perceived the platform to be near the helium-rich air and further into normal air. So it doesn’t matter what bats learn from the environment in which they were grown. The perception of the speed of sound is the same. This suggests that perception has it. The birth of the bat

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It’s a little surprising, as bats experience changes in weather and altitude, which can also change the speed of sound, often in excess of five percent. It would therefore seem helpful to be able to conditionally adjust the reflection position, but Amichai and Yovel put the adult bats in the helium environment for a few weeks and found no indication that the bats could adjust their perception. Can be where the feeding station is This was true even in an atmosphere containing 27 percent helium, so the bats’ knowledge of the velocity of sound appears to be locked into place.

Is it important or not? It’s hard to say. Experimental bats often fail to land properly. But it could be due to the aerodynamic lift difference caused by the change in pressure. In contrast to echolocation, bats appear to make adjustments here, sweeping their wings at a wider angle to compensate for the lack of lifting.

In any case, flight problems did not affect the perception of bats’ distances. Bats often begin echolocation before they fly off. This is an indication of how far the bat thinks the feeding station is.

Therefore, although it is helpful to have a more exact distance perception under a variety of conditions. But bats don’t seem to have improved their perceptual abilities. That may be because the advantages are not enough to make a difference. Or it could be offset by a competitive advantage, such as the ability to perceive relatively precise distances without learning, which could make a huge difference in the animal’s early flights.

PNAS, 2021 DOI: 10.1073 / pnas.2024352118 (About DOI)


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