Mapping the world with the speed-of-sound …

Vision and hearing are akin in that each interprets detections of reflected waves of energy.

1. Vision processes light waves that travel from their source, bounce off surfaces throughout the environment and enter the eyes.
2. Similarly, the auditory system processes sound waves as they travel from their source, bounce off surfaces and enter the ears. Both neural systems can extract a great deal of information about the environment by interpreting the complex patterns of reflected energy that their sense organs receive.
3. In the case of acoustics/sound these waves of reflected energy are referred to as echoes.

Unlike most humans, who map the world visually in units of distance, echo-locating creatures map the world in units of time or to be more accurate, the speed-of-sound. These animals, such as bats, whales, and dolphins, perceive an object as being at a distance of milliseconds (time), and not as being at a distance of meters (length), as was thought until now.

Acoustic / Sound Location:

Acoustic/Sound location is a method of determining the position of an object or sound source by using sound waves. Location can take place in gases (such as the atmosphere), liquids (such as water), and in solids (such as in the earth).

Location can be done actively or passively:

• Passive acoustic location involves the detection of sound or vibration created by the object being detected, which is then analyzed to determine the location of the object in question.
• Active acoustic location involves the creation of sound in order to produce an echo, which is then analyzed to determine the location of the object in question.

Both of these techniques, when used in water, are known as sonar; passive sonar and active sonar are both widely used.

Echolocation is a technique used by living creatures (both plants and animals) to determine the location of objects using reflected sound. In the case of animals, his allows the creature to move around in pitch darkness, so they can navigate, hunt, identify friends and enemies, and avoid obstacles.

More than one “types” of echo-location are defined:

Human echolocation: This is the ability of humans to detect objects in their environment by sensing echoes from those objects, by actively creating sounds: for example, by tapping their canes, lightly stomping their foot, snapping their fingers, or making clicking noises with their mouths. People trained to orient by echolocation can interpret the sound waves reflected by nearby objects, accurately identifying their location and size.
Some blind people are skilled at echolocating silent objects simply by producing mouth clicks and listening to the returning echoes.

Animal echolocation:
Echolocation, also called bio sonar, is a biological active sonar used by several animal groups, both in the air and underwater. Echolocating animals emit calls and listen to the echoes of those calls that return from various objects near them. They use these echoes to locate and identify the objects. Echolocation is used for navigation, foraging, hunting prey, and even communication.

Echolocating animals include mammals, especially odontocetes (toothed whales) and some bat species, and, using simpler forms, species in other groups such as shrews. A few bird species in two cave-dwelling bird groups echolocate, namely cave swiftlets and the oilbird.

Cave swiftlet (Collocalia linchi):

Oilbird (Steatornis caripensis):

A new study at the Tel Aviv University has revealed, for the first time, that bats know the speed of sound from birth. In order to prove this, the researchers raised bats from the time of their birth in a helium-enriched environment in which the speed of sound is higher than normal. They found that unlike humans, who map the world in units of distance, bats map the world in units of time. What this means is that the bat perceives an insect as being at a distance of nine milliseconds, and not one and a half meters, as was thought until now.

In order to determine where things are in a space, bats use sonar — they produce sound waves that hit objects and are reflected back to the bat. Bats can estimate the position of the object based on the time that elapses between the moment the sound wave is produced and the moment it is returned to the bat. This calculation depends on the speed of sound, which can vary in different environmental conditions, such as air composition or temperature.

For example, there could be a difference of almost 10% between the speed of sound at the height of the summer, when the air is hot and the sound waves spread faster, and the winter season. Since the discovery of sonar in bats 80 years ago, researchers have been trying to figure out whether bats acquire the ability to measure the speed of sound over the course of their lifetime or are born with this innate, constant sense.

Now, researchers led by Prof. Yossi Yovel, head of the Sagol School of Neuroscience and a faculty member of the School of Zoology in the Faculty of Life Sciences and his former doctoral student Dr. Eran Amichai have succeeded in answering this question.

The researchers conducted an experiment in which they were able to manipulate the speed of sound. They enriched the air composition with helium to increase the speed of sound, and under these conditions raised bat pups from the time of their birth, as well as adult bats. Neither the adult bats nor the bat pups were able to adjust to the new speed of sound and consistently landed in front of the target, indicating that they perceived the target as being closer — that is, they did not adjust their behavior to the higher speed of sound.

Because this occurred both in the adult bats that had learned to fly in normal environmental conditions and in the pups that learned to fly in an environment with a higher-than-normal speed of sound, the researchers concluded that the rate of the speed of sound in bats is innate — they have a constant sense of it. “Because bats need to learn to fly within a short time of their birth,” explains Prof. Yovel, “we hypothesize that an evolutionary ‘choice’ was made to be born with this knowledge in order to save time during the sensitive development period.”

Another interesting conclusion of the study is that bats do not actually calculate the distance to the target according to the speed of sound. Because they do not adjust the speed of sound encoded in their brains, it seems that they also do not translate the time it takes for the sound waves to return into units of distance. Therefore, their spatial perception is actually based on measurements of time and not distance.

Prof. Yossi Yovel: “What most excited me about this study is that we were able to answer a very basic question — we found that in fact bats do not measure distance, but rather time, to orient themselves in space. 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.”

Reference: “Echolocating bats rely on an innate speed-of-sound reference” by Eran Amichai and Yossi Yovel, 5 May 2021, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2024352118

It has been suspected by some researchers that dolphins employ a sono-visual sense to ‘photograph’ (in sound) a predator approaching their family pod, in order to beam the picture to other members of their pod, alerting them of danger.

Through the use of a CymaScope instrument, a device that makes sound visible, to gain a better understanding of how dolphins see with sound, John Stuart Reid was able to provide the first glimpse into what the dolphins might be ‘seeing’ with their sounds.

There is strong evidence that dolphins are able to ‘see’ with sound, much like humans use ultrasound to see an unborn child in the mother’s womb. The research team also postulates that dolphins are able to perceive stereoscopically with their sound imaging sense. Since the dolphin emits long trains of click-pulses it is believed that it has persistence of sono-pictorial perception, analogous to video playback in which a series of still frames are viewed as moving images.

John Stuart Reid has found that any small part of the dolphin’s reflected echolocation beam contains all the data needed to recreate the image cymatically in the laboratory or, he postulates, in the dolphin’s brain. Our new model of dolphin language is one in which dolphins can not only send and receive pictures of objects around them but can create entirely new sono-pictures simply by imagining what they want to communicate.

Dolphins appear to have leap-frogged human symbolic language and instead have evolved a form of communication outside the human evolutionary path. Reid concluded that “in a sense we now have a ‘Rosetta Stone’ that will allow us to tap into their world in a way we could not have even conceived before”.