I bet you must have overheard a person say that someone is as blind as a bat.
Well, sorry to burst that bubble, bats can see. Though they may have reduced sight, mesopic vision, which implies their vision is good to detect light at low levels. Humans and other mammals, on the other hand, has a photopic vision; the ability to see better and in colour.
But bats have a unique feature that helps them navigate around obstacles in the dark or hunt, e.g., capture an insect in the night. That secret is echolocation.
Echolocation is merely the use of echoes that some animals use in identifying objects in their vicinity. They send out pulses and wait for the echoes to bounce off objects, they process the received echoes which they use to avoid colliding with each other as they fly or hunt. It can be seen as the building of an "auditory image."
It is so an important subject, an associate professor from Virginia Polytechnic Institute and State University, located in Blacksburg Virginia, USA, Rolf Müller, is studying the behaviors of the bat to improve aviation. You can get the full details of their study to help make better submarines and drones in this video.
Echo Location in Mammals
A Whale of a Time
First on the list is whales, these gigantic kings/queens of the marine kingdom have a way with signals.
The series of clicks as it tracks a prey increases as it nears it. The sometimes audible buzz is mistaken for a song.
Their "song" lies in the range of 10 to 200 kHz. The sperm whale can detect food (prey) from an incredible distance of 500 meters. Please, someone, remind me not to go swimming in the ocean any time soon.
This distance beats the bat's miserly detection distance of 2 to 10 meters. But when you consider the whale is in sea water, and the speed of sound in water is 1531 m/s. This value is more than five times the speed of sound in air at 300 m/s.
Also, the bat weighs less than a gram while a whale could weigh up to 50 tons (45359.2kg).
So when next you hear a whale "singing," just know it may be giving off a warning to other family members to steer clear of something, finding a way home or just plainly hunting for dinner or lunch.
It's the dolphins
The whales, while very big are not the only marine tenant with the skill of echolocation. The dolphins do just fine too. Like the bat, they can see, but their vision is not that great. They push air through their nasal passages which creates high-frequency pulses through the water. The fat-filled area of the head, called the melon, behaves like a concentrator that focuses the sound waves to a particular direction.
The reflected signals first hit the forehead and lower jaw which redirects the sound to the middle ears which send the signal to the brain for processing and interpretation.''
Daredevil in Real Life
The Daredevil, an Amerian comic book character is a man you do not want to mess with. He may be blind as a result of radioactive exposure when he saved a man from being run over by a truck by pushing him to safety. But his other senses are extraordinarily heightened that he goes about saving the day by ensuring the bad guys do not get to operate in his neighborhood.
But a real-life boy, Ben Underwood, born in 1992 and lost his sight at the age of three as a result of retinal cancer (cancer of the eye).
He was able to do a lot of incredible things that sighted people could do, simply by making clicking noises and listening to the echoes. He can ride a bike like a pro, or play basketball, do rollerskating, hang out with the dolphins, etc.
This feat is possible because echolocation works with the principle of sending out signals and waiting for their echoes. It is a unique ability which only very few humans have been able to master. Though animals, on the other hand, seems to have the upper hand in this game of echoes.
A human brain is a fantastic tool that never ceases to amaze us. The speed of sound in air at 20 degree Celsius is 300 meters/second. But the ear can sense or detect a pulse-to-echo delay, even though it cannot hear the difference or the separation between the outgoing click and return echo; of up to 0.0003 seconds or 0.3 milliseconds.
Though the human brain is awesome, our animal friend, the bat, is the clear winner here as it can sense up 10 x 12 nanoseconds or 1 x 10 -8 seconds, i.e., 1/100,000,000 seconds pulse-to-echo delays!
It's all in the brain
A study carried out by Thaler published in 2014 looks at the brain's neural correlation between the blind, and the sighted as they process the recording of both echoes and clicks which was made by the participants beforehand.
They used the magnetic resonance imaging device which captures the brain neural activities as it tries to process data.
The blind expert's brains lit up like a Christmas tree in the area of the brain (cortex), known as the V1 or the primary visual cortex, an area an individual with regular sight uses for vision processing.
The control, the normal sight participant's brain showed no sign to the sound.
This result was surprising, to say the least as it signifies the blind uses this part of the brain for the vision of the sighted, for echolocation.
The reorganization or remapping shows the plasticity or the ability of the brain of the blind echolocators to reassign the visual processing area of the brain, instead of the auditory side, for use in the echolocation computation.
This same plasticity of the brain helps the heightening of one sense over the others. E.g., most blind people have a better sense of touch than people with all the senses. Thus the auditory or olfactory sensitivities may be better for someone who lost their sense of vision.
References
Getting around by sound: Human echolocation