Seeing in the dark

comments 3
Anthropology / Evolution / Myths / Zoology

You’ve probably heard of echolocation. Whales, dolphins and bats all use it to find their way around when their eyes just aren’t up to the task. But did you know some blind humans have learned to do it too?

What do bats, beluga whales and certain talented blind people have in common? Echolocation. Image credit: Киты via Wikimedia Commons

Seeing with sound

In the late 1700s, Italian scientist Lazzaro Spallanzani surgically blinded bats in an attempt to work out how they navigate when flying in the dark. He was amazed to discover blind bats could avoid obstacles just as well as sighted bats. But when he blocked the bats’ ears, they started crashing into things. His logical conclusion: bats find their way using hearing.

We now know a lot about how they do it. Most insect-eating bats call or make tongue clicks as they fly at night (or in caves) and listen carefully to the echoes of these sounds as they bounce off nearby objects. Most of these sounds are ultrasonic, which means they are too high-pitched for us to hear. Lucky, because some bats produce sounds louder than a smoke detector ten centimetres from your ear. Bats use these sounds to paint a detailed picture of the world around them including the food they are trying to catch. Imagine a bat chasing a moth in the dark: with echolocation, the bat can work out the moth’s size, location, and the speed and direction it is flying. Scientists that developed sonar and radar navigation systems are said to have got the initial idea from bat echolocation.

Under the sea

Echolocation doesn’t just come in handy at night – it’s also a massive to help to animals living in water. Light doesn’t travel well through water, meaning it’s hard to see underwater. But sound travels more than four times faster through water than air. So it’s not surprising some water-living animals use biosonar.

‘Toothed’ whales (which include dolphins and porpoises) all use echolocation and fossils suggest they evolved the ability millions of years ago. Bats and whales are no more closely related than a mouse and an elephant, but they’ve come up with the same nifty trick to get around and find food. The way whales use echolocation depends on the food they are hunting for. The exact way they produce the sound also varies. Dolphins send out series of very quick, high-pitched sounds by forcing air through their nasal passages. Research suggests the mucus – snot – covering these passages is essential for making these sounds successfully.

Narwhals, affectionately called the unicorns of the sea because of their huge horn (which is actually a giant tooth), are thought to have the most accurate biosonar of all. Narwhals live in the Arctic where it’s dark more than it’s light, and there’s more ice than open sea. But as mammals, they still need to come to the surface to breathe, on average every four to six minutes. To survive, they need to find rare cracks in the ice to breath. They also need to find squid and fish in complete darkness: they hunt during dives that can be as deep as 300 metres beneath the surface. How do they do it? By making up to 1,000 clicks per second and creating a detailed picture of what’s around them using the echoes that bounce back.

‘The remarkable batman’

It’s not surprising humans aren’t known for our echolocation abilities – most of us have exceptionally good vision, and have no need to see with sound. Except of course, people who are blind. And we now know some blind people have developed incredible echolocation abilities.

Most famously, Daniel Kish, who lost both eyes to cancer before he was one-and-a-half years old. Daniel makes clicking sounds with his tongue and creates an image in his mind with the echoes, exactly as bats and whales do. He calls it ‘flash sonar’ and his abilities have earned him the nickname ‘the remarkable batman’. Among many other things, Daniel successfully rides a bike using this technique. As an extra bonus, his sonar works just as well behind him as in front, and works around corners. Daniel is president of an organisation, World Access for the Blind, which trains blind people to use echolocation.

The only reason sighted people can’t do it is they don’t have to – Daniel Kish

Recent research has shown that given the opportunity, sighted people can learn to work out the relative sizes of rooms using only echo information. One study participant became so good at it, he could tell if there was as little as four percent difference in the size of two rooms by listening to the sound of his tongue clicks. Another study found most sighted people can become reasonably good at echolocation with two to three weeks of training. A key to successful echolocation is moving the head – which mimics the way bats turn their ears when echolocating.

Studies have shown the visual cortex in experienced echolocators brains is highly active when echolocating. This area is usually devoted to processing visual information. But it seems in echolocators, the region has been repurposed to give extra capacity to sound instead.

Just another reminder of how incredibly versatile our brains are.

Links and stuff

3 Comments

  1. Daniel is incredible and who would have thought that what could be considered a disability has an alternate option that gives you even more than sight.

    • Amazing isn’t it. If you listen to the Invisibilia podcast you get to hear his Mum’s philosophy and why he ended up so fearless and capable. And now he’s teaching others to be the same way.

Please, let me know what you think.

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s