A new study by Tel Aviv University has proven that bats identify objects in space only by the time it takes for sound to rebound off of them. What's more, researchers have discovered that bats are inherently born knowing the speed of sound.
Bats use echolocation to detect prey, perceive objects around them, navigate, and avoid collisions much in the same way that humans use sight. The animals contract their larynx or click their tongues to produce sound frequencies between 5 kHz – 200 kHz (Weizmann Institute of Science), which when reflected back, provide them with an image of their surroundings based on the travel time and alterations in the sound.
The researchers wondered how bats would react to a change in the speed of sound. Would they adapt or grow confused?
Though the speed of sound is generally around 343 m/s in dry air at 20 degrees Celcius, temperature rises and humidity levels can affect the rate of sound travel. To artificially increase the speed, scientists placed adult and infant bats in helium-enriched air.
The result was that the adult and bat pups continuously missed their targets, erroneously thinking they were closer. The bats seemed to have an ingrained sense of the speed of sound and judged the objects by that rate, not adjusting to the change.
Scientists previously assumed that bats calculated the distance of an object through the time its echo took to return. Similar to the famous physics problem, when a pebble is dropped into a well, the depth can be calculated using the speed of sound and the time it takes for it to hit the bottom and echo back a splash. The longer the pebble falls, the deeper the well.
However, this study indicated that the bats don't calculate the physical distance at all, but instead perceive the objects by time alone. Since the speed of sound carried their calls faster, that bats' judgments were skewed.
"We found that in fact, bats do not measure distance, but rather time, to orient themselves in space," Prof. Yossi Yovel, the head of the study said. He led the research along with Dr. Eran Amichai."This may sound like a semantic difference, but I think that it means that their spatial perception is fundamentally different than that of humans and other visual creatures, at least when they rely on sonar. It's fascinating to see how diverse evolution is in the brain-computing strategies it produces."