“Seeing” with the Ears. Can bats hear in colour? – with Polish translation

Jul 14, 2013

Photons travel fast in straight lines, and can be focused with huge precision. This provides the opportunity to compute highly detailed, accurate information about the world. We are familiar with this, and we take it for granted that our eyes and associated brains enable us to navigate our way around obstacles at high speed, and hit a fast moving target like a tennis ball. We really notice the difference when darkness reduces us to helpless stumbling.

But there is a living to be made during the dark half of the day-night cycle, and it is now well known that bats have evolved the capacity to “see” without light, using their highly tuned ears rather than eyes (indeed the more specialised bats have all but completely lost their eyes). Echoes of high pitched sounds are not quite as good as well focused light but, with suitable processing in the brain, they enable the bat to fly at high speed between stretched wires without getting injured, and to catch insects on the wing, all in total darkness. Toothed whales have evolved the same “echolocation” skill (especially highly developed in river dolphins swimming and hunting in murky water where seeing is almost impossible) and by two separate groups of cave-dwelling birds.

I have long conjectured that the answer to the famous philosophical question, “What is it like to be a bat?” might be “Pretty much the same as to be a fast flying, visually hunting insectivorous bird such as a swallow.” I meant something rather specific by this. When visual animals such as swallows or people look at the world, we construct a simulation model in the brain, which is continuously updated by incoming data from the eyes, and hence bears enough similarity to the real world outside to allow navigation through it and pursuit of moving targets. The remarkable phenomena of visual illusions are best interpreted on the hypothesis that what we “look at” is not the real world itself but our internal model of it.

When the ancestors of bats and dolphins began to use echolocation, probably tens of millions of years ago, their brains already contained sophisticated simulation software, sensitively tailored to perform the mathematical calculations necessary for high speed manoeuvring. Rather than let that originally visual software languish idle, it would have been entirely natural to commandeer it to the service of the new skill, echolocation. All that was needed was a new “driver” module (to pursue the computer metaphor), that allowed echoes to update the simulation rather than retinal images. This is why I conjectured that bats “see” with their ears. The scene, as perceived by an echolocating bat, might look very much like what a swallow sees, because both bat and bird are deploying the same kind of simulation model, to perform the same kind of task.

I even stuck my neck out (for example in Unweaving the Rainbow) and wondered whether bats use colours (I meant the subjective sensations or qualia that we call red, blue, green etc.) as labels for different echoic textures of objects: perhaps “red” for shiny, hard surfaces like locust abdomens, “blue” for soft furry moths. “Red” and “blue”, after all, are only arbitrary labels for light of different wavelengths. There is nothing inherently “red” about 700 nanometres. Given that colour qualia were lying about in the brain and no longer needed as labels for wavelengths of light, why not press them into service again as labels, but labels of something else, namely echoic texture?

I was therefore intrigued to read the inspiring story of Daniel Kish in yesterday’s Guardian. At the age of one, he had both his eyes surgically removed to save him from an aggressive eye cancer. For as long as he can remember, he has been making clicking noises with his tongue, and using them to find his way around. It wasn’t until he was ten that a friend pointed out to him that he was doing what bats do: echolocation:

Every surface has its own acoustic signature – I can recognise a tree, for example, because the trunk produces a different echo from the leaves. The hard wood reflects the sound, whereas the leaves reflect and refract, too, scattering the sound waves. Everything around me becomes identifiable with a click. It provides me with a 3D image in my mind with depth, character and richness; it brings light into darkness. I can often find my way out of an auditorium quicker than a sighted person because I can identify the exit. If I'm in a noisy place such as a concert, I don't feel anxious – I just increase the volume and my click cuts through the noise. I'm very familiar with its sound and don't feel at all self-conscious if other people hear me.

I don't have superhuman hearing, even though I'm sometimes called Batman; I have just trained my ears to understand the echoes. Anyone could do it, sighted or blind – it's not rocket science. If you hold up a book in front of you and click, then take it away and click, you can hear a difference, just as you know you're in an empty room because it's echoey. When I was in college I wrote my thesis on echolocation, and during my research I had to consciously deconstruct how I was doing it to understand the process. I know there's a wall in front of me, I'd think, but what's tipping me off? I would set myself tasks and try to get quicker and quicker at navigating obstacle courses.

His ability is so surprising to sighted people that they annoyingly treat him as far more disabled than he is:

. . . although I have travelled around the world successfully, when I'm in an airport I feel that officials yearn to get me in a wheelchair, take away my documents and leave me feeling powerless. One friend wasn't allowed to leave the plane until "assistance" arrived, even though he held the world record for blind cycling; he was too nice to make a fuss but I would have insisted.

I have made it my life's work (http://www.worldaccessfortheblind.org) to teach blind children how to empower themselves using echolocation, which I call flashsonar. As you become more adept, you also click more subtly and naturally, like blinking, so often people around you aren't aware you're doing it and you aren't stigmatised for it.

He even taught himself to ride a bicycle:

Now I can ride along a busy street or go on a trail in the woods. I have never hit a pedestrian – touch wood – because I don't ride on the pavement. Cars are excellent echo targets, so I can easily avoid them. I won't say I've never had an accident, but every activity holds an element of risk.

Negotiating rush hour traffic isn't my dream; I am just glad I can if I want to. It's ironic – I spend all my time encouraging blind people to be active participants in society when, really, I'd love to step out of it. When my work is done, you'll find me in the mountains like an old hermit, with just my clicks for company.

We need not suppose that a person could ever become as good at echolocation as a bat. Bats have had millions of years of evolution to perfect their skills and tune up their brain software. Moreover, the clicks that bats use are ultrasonic – too high for humans to hear – and this greatly improves the accuracy of the echolocation, for reasons that physicists well understand. Engineers can make instruments that beam ultrasonic clicks, and instruments that can transpose ultrasound down to audible frequencies. I have myself donned an experimental headset, designed by L.Kay in New Zealand to be worn by blind people, and after only a few minutes of practice was able to get a rudimentary idea of my surroundings, though blindfolded.

(Referenced in http://etheses.nottingham.ac.uk/1655/1/467746.pdf)

I should love to know whether there is any truth in my conjecture that echoes make it possible to “hear colour”. Does Daniel Kish hear colour? He himself might be unable to answer the question because he lost his sight probably too young to remember what it was like. But he also tells us there are others who have the same skill as him. If any of them lost their sight when old enough to remember it, dare we hope for eye witness (ear-witness?) testimony that “seeing with the ears” really can become – after a lot of practice – the same subjective experience as seeing with the eyes? And do any of them actually “see” in colour? If they do, it seems a safe bet that bats do too. If they don’t (which I must say seems more likely) that doesn’t mean that bats don’t either: remember once again that bats have had millions of years in which to perfect their echolocation system.

Read the story of Daniel Kish here:




Czy nietoperze mogą słyszeć w kolorze?

Autor tekstu: Richard Dawkins

Tłumaczenie: Małgorzata Koraszewska

Fotony podróżują po liniach prostych i można je skupić z wielką precyzją. Daje to możliwość wykalkulowania bardzo szczegółowej, dokładnej informacji o świecie. Dobrze to znamy i traktujemy jako oczywistość, że oczy i skojarzone z nimi mózgi umożliwiają nam znajdowanie z dużą prędkością drogi wokół przeszkód oraz trafianie w poruszający się cel, taki jak piłka tenisowa. Zauważamy różnicę, kiedy ciemność redukuje nas do bezradnego potykania się. 

Podczas ciemnej połowy cyklu dzień/noc istnieje jednak możliwość zarobienia na życie i dobrze wiemy teraz, że nietoperze wyewoluowały zdolność „widzenia" bez światła, używając swoich wspaniale nastrojonych uszu zamiast oczu (w rzeczywistości bardziej wyspecjalizowane nietoperze niemal całkowicie straciły oczy). Echo dźwięków o wysokiej częstotliwości nie jest tak dobre jak skupione światło, ale z odpowiednim przetwarzaniem w mózgu umożliwia ono nietoperzowi latanie z dużą prędkością między napiętymi drutami bez zranienia się, oraz łapania w locie owadów, a wszystko to w całkowitej ciemności. Walenie zębowce wyewoluowały te samą umiejętność „echolokacji" (szczególnie wysoko rozwinięta u delfinów rzecznych, które pływają i polują w mętnej wodzie, gdzie widzenie jest niemal niemożliwe), jak również zrobiły to dwie różne grupy żyjących w jaskiniach ptaków.

Długo wyobrażałem sobie, że odpowiedzią na słynne pytanie filozoficzne „Jak to jest być nietoperzem?" może być „Całkiem podobnie do bycia szybko latającym, polującym na owady ptakiem, takim jak jaskółka". Rozumiałem przez to coś dość konkretnego. Kiedy widzące zwierzęta, takie jak jaskółki lub ludzie, patrzą na świat, tworzymy w mózgu model symulujący, który nieustannie uaktualniamy danymi, dostarczanymi nam oczy, a więc jest on wystarczająco podobny do rzeczywistego świata, by pozwolić nam na poruszanie się w nim i pogoń za ruchomymi celami. Te zdumiewające zjawiska iluzji wzrokowej najlepiej interpretować na bazie hipotezy, że to, na co „patrzymy", nie jest rzeczywistym światem, ale naszym wewnętrznym modelem świata.

Czytaj dalej

Written By: Richard Dawkins
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