Compared to animals, humans have relatively limited senses. We can't smell as well as dogs, see as many colors as birds, or find our way home using Earth's magnetic poles as sea turtles do. But there is an animal sense we can learn from: we might call it "bat-like echolocation." Our topic is “People Can Develop a Sixth Sense”.
Researchers in Japan have demonstrated in a paper published in the journal PLoS One that this sixth sense can be developed and that humans can use echolocation to describe the shape and rotation of various objects in the absence of light.
If people can recognize these three-dimensional acoustic patterns similarly, it could literally expand how we see the world, says Dr. Sumiya of the Center for Information and Neural Networks in Osaka, Japan.
As bats move around objects, they send out high-pitched sound waves that return to them at different intervals of time. This helps tiny mammals learn more about the geometry, texture or movement of an object.
“Studying how humans acquire new sensing abilities to recognize environments using sounds or echolocation could lead to an understanding of the resilience of the human brain,” says Sumiya.
“We can also gain insights into the detection strategies of other species by comparing it with information gained in studies of human echolocation.”
What is echolocation?
Human echolocation is the ability of people to perceive objects in their environment by detecting echoes from those objects, actively creating sounds: for example, by tapping their cane, tapping their feet, snapping their fingers, or making clicking noises with their mouths. Persons trained in echo navigation can accurately determine their position and size by interpreting sound waves reflected from nearby objects.
If we go back to our work;
This is not the first study to show echolocation in humans. Previous studies have shown that visually impaired people can use mouth click sounds to "see" two-dimensional shapes. But Sumiya says this study is the first to discover a specific type of echolocation, called time-varying echolocation. Beyond locating an object, time-varying echolocation will enable human users to better perceive the object's shape and motion.
Sumiya's team gave participants headphones and two tablets to test the subjects' echolocation detection abilities, one to generate synthetic echolocation signals and the other to listen to the recorded echoes.
In a second room that the participants couldn't see, two oddly shaped cylinders were either spinning or standing still. The cross-section of these cylinders is similar to a four- or eight-spoke bicycle wheel.
When prompted, 15 participants initiated echolocation signals via the tablet. Sound waves oscillate as pulses and enter the second chamber and then hit the cylinders.
It took some creativity to transform the sound waves into something human participants could recognize. “The synthetic echolocation signal used in this study included high-frequency signals up to 41 kHz that humans couldn't listen to,” explains Sumiya.
For comparison, they are bat echolocation signals in the wild range from 9 kHz to 200 kHz. It is well outside of our 20 Hz to 20 kHz hearing range.
The researchers used a one-seventh scale dummy head with a microphone in each ear to record sounds from the second room before transmitting them back to the participants.
The microphones made the echoes double-voiced, much like the surround sound you might encounter in a movie theater or when watching an autonomous sensory meridian response (ASMR) video recorded using a pair of ear microphones. The frequency of the signals was also lowered when Sumiya was picked up by the miniature head to one-eighth of the original frequency, so that human participants could hear them "with the feeling of listening to real spatial sounds in a 3D space."
Finally, the researchers asked participants to determine whether the echoes they heard came from a rotating object or a stationary object. Finally, the participants were able to reliably identify the two cylinders by listening to the pitch and using the time-varying echolocation signals reflected from the rotating cylinders.
How Visually Impaired People Develop a New Sense
Losing one sense can elevate the others. This is a phenomenon known as neural reuse or neural reuse, in which the brain adapts and amplifies the remaining senses.
Making clicking noises with their mouths has helped some visually impaired people improve their ability to use two-dimensional echolocation.
Research shows that a part of the brain involved in visual processing (the primary visual cortex located in the occipital lobe) can reconfigure itself to process echoes from clicks as visual stimuli.
In essence, the brain can "see" the echoes as they bounce back and use the sound to help a person reconstruct the space and objects around them.
This gave some echolocators the ability to plot a room and its contents simply by walking around, making clicking noises and listening for echoes.