Friday 27 July 2012

Echolocation: a sound choice?

In January I wrote a post on whether detecting heat could supplant vision, and concluded that it was, in fact, just a form of sight. I wished to tackle echolocation next, but wondered where to start: with echolocating animals in fictional biology? Other possible questions would be which atmosphere would be best, which frequencies to use, how it can be compared with vision, etc. In the end I decided to start -there's more!- with a post on the nature of echolocation; so here we go...

The basic principle is simple: you send out a sound and if an echo returns, there is something out there. As everyone knows, dolphins and bats are expert echolocators., but it is less well known that some blind people are quite good at it, and that they in fact use their occipital cortex to process echoes, a brain region normally busy with analysing visual signals. That direct link between vision and echolocation is perhaps not that surprising, as both senses help build a spatial representation of the world outside: what is where?

A major difference between vision and echolocation is how distances are judged. In vision, judging distances depends on complex image analysis, but in echolocation the time between emitting a sound and the arrival of the echo directly tells you how far an object is away. The big problem here is that echoes are much fainter than the emitted sound. The reason for that is the 'inverse square law', something that works for light as well as for sound.

Click to enlarge; copyright Gert van Dijk

The image above explains the principle. Sound waves emanate from a source near the man in the middle and spread as widening spheres (A, B and C). As the spheres get bigger, the intensity of the sound diminishes per 'unit area'. A 'unit area' can be a square meter, but can also be the size of your ear. When you are close to the source your ear corresponds to some specific part of the sphere, and when you move away your ear will correspond to a smaller part of the sphere: the sound will be less loud. Now, the area of the sphere increases with the square of the distance. If you double the distance from the source, the area of the sphere increases fourfold, and the part your ear catches will decrease fourfold. To continue; increase the distance threefold and the volume decreases ninefold. Move away ten times the original distance from the source, and the sound volume becomes 100 times smaller!
In the image above, only a tiny fraction of the original sound will hit the 'object', a man, at the left. Not all of that will bounce back, and the part that is reflected forms a new sound: the echo. The echo in tun decreases immensely before arriving at the sender, and that is the essence of echolocation: to hear a whisper you have to shout.

Click to enlarge; copyright Gert van Dijk

As if the 'inverse square law' is not bad enough, there is another nasty characteristic of echolocation. At the left (A) you see a random predator using echolocation. Oh, all right, it's not random, but Dougal Dixon's 'nightstalker' (brilliant at the time!). It sends out sound waves (black circles) of which a tiny part will hit a suitable prey; there's that man again. As said, the echoes travel back while decreasing in strength (red circles).
There will be some distance at which a prey of this size can just be detected. Any further away and the returning echoes will be too faint to detect. Suppose that this is the case here, meaning 10m is the limit at which a nightstalker can detect a man (as mankind is extinct in the nightstalker's universe no-one will be hurt).
Here's the catch: most of the sound emitted by the nightstalker travels on beyond the prey. These sound waves can be picked up easily by other animals further away than 10 meters (I assume you recognise the creature listening there; it's pretty frightening). For animals out there the sound only has to travel in one direction and none of it gets lost in bouncing back from the prey. The unfortunate consequence of all this 'shouting to hear a whisper' is that the nightstalker is announcing its presence loudly to animals that it cannot detect itself!
This suggests that echolocation could be a dangerous luxury. One way to use it safely would be if other predators cannot get to you anyway. Is that why bats, up there in the air, can afford echolocation? Another solution would be to be big and bad, so you can afford to be noisy? If so, echolocation is not a suitable tool to find a yummy carrot if you are an inoffensive rabbit-analogue. The carrot does not care, but the wolf-analogue will.


Getting back on topic, we now know that echolocation tells you how far away an object is. To make sense of the world you will also need to know where the object spatially: left and right and up and down. With hearing this is more difficult than with vision, but it can be done. The spatial resolution of bats is one or two degrees (see here for that), which is impressive but still 60 to 120 times less good than human vision. For now, let's take it for granted that an echolocating animal can locate echo sources. Next, let's try to visualise what it may be like.

Click to enlarge; copyright Gert van Dijk

Here is a scene with a variety of objects on a featureless plain. The objects have transparency, colours, shadows, etc. At one glance we see them all, as well as the horizon, the clouds, etc., without restrictions regarding distance, all in high resolution. The glory of vision, for all to see.

Click to enlarge; copyright Gert van Dijk

Colour is purely visual, so to mimic echolocation it has to go. All the objects are now just white. They are also all featureless, but that is for simplicity's sake only: vision and echolocation can both carry information about things like wrinkles and bumps, so I left texture out.

Click to enlarge; copyright Gert van Dijk

In sight the main source of light is the sun shining from above, but in echolocation you have to provide your own energy. To mimic that, the only light source left is at the camera. The resulting image looks like that of a flash photograph, for good reasons: the light follows the inverse square law, as does sound. Nearby objects reflect a lot of light (sound!) for two reasons: they are close by, and part of their surfaces face the camera squarely, turning light directly back at the camera. This is an 'intensity image'.

Click to enlarge; copyright Gert van Dijk

However, you can see nearby and far objects at the same time, but that is not true for sound. Sound travels in air at about 333 m/s, so sound takes about 3 ms to travel one meter. An object one meter away will produce an echo in 6 ms: 3 ms going to the object and 3 ms travelling back. The image above shows the same scene, but now the grey levels indicate the distance from the camera. Light areas in the image are close by, dark areas are further away. This is a 'depth image', formed courtesy of the ray tracing algorithms in Vue Infinite.

Copyright Gert van Dijk

Now the scene is set to mimic echolocation. Let's send out an imaginary 'ping'; each interval in time determines how far away an echo-producing object is. For instance, the interval from 6 to 12 ms after the 'ping' corresponds to objects 1 to 2 meters away. While the depth image tells us how far away objects are, the intensity image tells us how much of an echo is produced there. To make things easier for the human eye a visual clue was added: echoes returning early are shown in red, while those returning later are blue. Above is a video showing three successive 'pings'. As the echoes bounce back, areas close by will light up in red, and objects furet away will produce an echo in blue, later on. I blurred the images a bit to mimic the relatively poor spatial resolution of echolocation.
I personally found it difficult to reconstruct a three-dimensional image of the world using such images, but my visual system is not used to getting its cues in such fashion.

Copyright Gert van Dijk

One easy processing trick to improve the image is to remember the location of early echoes. The video above does that, by adding new echoes without erasing the old ones. The image is wiped as a new ping starts. More advanced neuronal analyses could take care of additional clues such as the Doppler effect, to read your own or an object's movement. By the way, the above is in slow-motion. In real life echoes from an object 10 m away would only take 60 msec to get back. Even without any overlap you could afford 16 pings a second for that range. That is not bad: after all, 20-25 frames a second is enough to trick our visual system into thinking that there is continuous movement.

So there we are. Is this simple metaphor a valid indication of what echolocation is like? Probably not, but it does point out a few basic characteristics of echolocation. Echolocation must be a claustrophobic: no clouds, no horizon, just your immediate surroundings. It would seem the meek cannot afford it, as it may be the most abrasive and abusive of senses.
Is it therefore completely inferior to vision? Well, yes and no...

Friday 13 July 2012

Salsa invertebraxa

Some books cannot be classified into a category with any ease; 'Salsa invertebraxa' is definitely such a book. It deals with fictional animals, which criterion by itself reduces the number of books in the putative category enormously. It is not told in a pseudoscientific manner as if the life forms in it actually exist. Dougal Dixon's books are pseudodocumentary in nature, and so is Barlowe's 'Expedition'. If Snaiad, Nereus or Furaha ever make it into book form, they will also fit in the same pseudofactual category. 'Salsa' does none of that; its focus is to tell a story of life through images. It deals with fictional insects functioning as characters with heart and wit, and does this admittedly surprising job brilliantly, I think. I first learned about it through the magazine ImagineFX, and then soon found it on the Behance site. I was intrigued but puzzled by the wonderful but complex images. I found reviews, but the reviewers seemed at a loss to describe what to make of the book. The author, Mozchops, has a page on DeviantArt as well as his own site. If you are interested you should visit all these sites, as they show a fairly large number of the digital paintings Mozchops produced for the book (there is a still larger number of unpublished paintings in the book though. When I found the site of the publisher, Pecksniff Press, I needed but a day or so to decide that I just had to have the book. It was promptly delivered a few days later, but meanwhile I had already contacted Mozchops (Paul Phippen), who was kind enough to explain one or two things about his work. So what is 'Salsa invertebraxa'? You could describe it as a 'graphic novel' telling the story of two insects, comrades from different species travelling through a forest. They are pranksters, stealing eggs from spiders and centipedes. They adorn themselves with the moulted exoskeleton from a cicada-like insect. Decked out in such fashion, they capture colourful caterpillars, suspend them from threads and ride them through the air as if they themselves are knights in armour sitting on war horses. While true, this description might cause the book to come across as silly or even childish. It is neither. It is in fact an extremely complex work that does not give away its secrets lightly. Working out the story needs attention to detail, and there is more to the story than just the above synopsis. The images themselves need careful analysis, because they are full of details and because the artist makes no concessions nor steps down to clarify what it is about. The reader has to rise to the challenge, one I personally enjoyed. There are bits of sparse text, but the words are there to evoke an atmosphere, certainly not as a legend to explain the images. I found myself studying the book several times, and only then did the story start to become clear in my mind. If you like your fantasy biology straight, with little arrows pointing to biological details, you may not like this book. But you would risk missing the incredibly capable artwork. There are certainly enough odd insect shapes in there to satisfy those who like alien animals. Or perhaps their shapes are the result of an alternate evolution on Earth; who knows? I do not think everything in this biology can work. For one thing, I very much doubt that there is space in an insect's head for the neural machinery needed to produce an intelligent prankster, but this is one of those instances where such criticisms are completely beside the point. Ignore it. On rereading the above text, I still doubt that it gives you a full idea what the book is about; you will probably have to read it yourself. I will show a number of images I chose that Mozchops was kind enough to send me in a high-resolution form.
Click to enlarge; copyright Mozchops 2011
Here is an early scene of the two protagonists flying about; the one on the left has clublike extremities while the other is mosquito-like. Just note the shimmer of the wings of the 'mosquito'; it takes skill and belief in your skills to dare paint motion-blurred wings like that, with so little indication of what you see.
Click to enlarge; copyright Mozchops 2011
This image is out on the web already, I think. The two heroes encounter an army of termites, armed to the teeth. I include it so you will get a feeling for how the text adds to the image.
Click to enlarge; copyright Mozchops 2011
Obviously, I could not resist including this one. Regular readers may remember that I did some calculations regarding 'ballonts' some time ago. I had to conclude, to my considerable irritation and disappointment, that my idea of filling Furahan skies with ballooning plankton was not going to work: small ballonts do not work. Luckily, Mozchops had not read that and had designed animals like that. He provided a twist to the idea that I like very much: you are probably all aware of the peculiar mating flight of some dragonflies: the male clasps the female by the neck using claspers on his abdomen. Together the two then fly around to deposit eggs in suitable places. Well, in Mozchops' view the male has a balloon instead of wings, and so the two can float around serenely. Aren't they wonderful? It makes me wish to ignore my own reasoning that small ballonts cannot work...
Click to enlarge; copyright Mozchops 2011
This is one you may have to look at for a while. One of the protagonists, the one with the clubby legs, is riding a caterpillar, as colourful as the saddle cloth of any mediaeval war horse with pennants trailing behind it.
Click to enlarge; copyright Mozchops 2011
At the end of the book the two are met by a host of insects working together as a troupe, the purpose of which is our guess. I wish to show it to you so you can see the inventiveness of the insect shapes. Note the one flying on the right, with its near-mechanical shape and its protruding tongs. The multi-species insect armada contains some of the most wonderful insect shapes in the book.
Click to enlarge; copyright Mozchops 2011
Click to enlarge; copyright Mozchops 2011
Here, a host of insects, from small to majestic, takes to the skies in an exodus the reasons of which we are not told. Mozchops was kind enough to send me an early sketch of this painting, which is an exclusive for this blog. I would like to draw your attention to one insect at the left, the one with twin booms sticking out backwards. I love its shape, with its twin booms evoking the shape of aircraft such as the P38-Lightning. Note that the entire painting is filled with many such inventions. Other people would probably be content to paint just one such design on one painting; here, we are spoilt for choice. All in all, this may be one of the oddest books I have, but it certainly is also among the ones I like best. It certainly deserves more attention, and I hope that this post helps bring that about.

Sunday 1 July 2012

The order electrus

From time to time I search the internet in a search for interesting machines that could lend themselves to be turned into an animal design, or that represent a technical version of a -much older- biological principle. For past examples, see here or here.

While doing so, I came across a website of a countryman of mine, one Jarno Smeets, who was apparently working on human powered flight. That has been done more than once, using propellers driven by a bicycle gear and chain transmission. But what this inventor proposed was that he was going to take of using his arms to provide the propulsion, by flapping the wings. Now that is simply not going to work: human arms are not strong enough to flap wings large enough to lift a human. I lost interest, until my attention was drawn to the site by other sources: now the site had a video purporting to show that he had actually done it. I did not believe it, which was just as well as otherwise I would have been one of many people fooled by the blog: it was all a hoax! The artist/perpetrator was Floris Kaayk. Here it is.

The video is cunningly made: it has all the nice clumsiness of a rather poorly executed home video. There is even someone shouting excitedly into the camera that the flight should have been recorded with another camera, from in front. What you do see is something flapping into the air from quite some distance, and then there are some shots of him flapping, and shots taken from a flying vehicle.

I was intrigued by the elaborate nature of the hoax and found that he Mr Kaayk had done more work bordering on the fantastic. I would like to show you one video in particular, 'The Order Electrus', as it comes close to the usual topics of this blog. It is a documentary showing 'life forms' consisting of electronics parts, running around like little robots. If ever artificial life comes into being, and I cannot think of any reason why this should be impossible, it will not look like this. But that does not matter too much here. As is often the case, when there is enough of a sense of humour, the need to be critical evaporates. I love the film's tongue in cheek attitude. As nature documentaries go, this is a very nice one. It follows here, but if you wish to see it in more detail, please visit Mr. Kaayk's website.