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Camouflage in Motion
Adrian writes "Remember Jurassic Park, where Goldbloom stood really still and the T-Rex couldn't see him? Well, there might be a better way. Scientists have found that dragonflies can dissappear by keeping their image on your retina in the same place, even if you move. How they manage it still has them puzzled... ;)"
What an incredibly hollow article. "We've used some technical majiggers to look at some stuff and wow! Look what we came up with!" It's a good thing there wasn't any actual details in there, it may have been interesting.
Al Qaeda has ninjas!
I've never seen a puzzled dragonfly. Oh. The scientists.
I'd assume that the dragonfly merely tries to keep the thing it's hiding from in the same position on *its* retina. It'd be a fairly simple feedback mechanism, if you did it with analogue electronics.
-Yarn - Rio Karma: Excellent
King Charles 'beheaded' guests who bored or annoyed him by viewing them at such an angle that his blindspot was over their head. Try it for yourself
Well duh. Didn't they ever catch flies when they were young? The way to do it is to take two fingers and follow the fly with them, maintaining the distance between your hand and the fly. after a while the fly will think your fingers are part of the background and will easily let you catch it.
x <- Moderators, keep staring at this point.
Everone else can look here -> x
Now, if my calculations are correct, I should be able to get away with this:
Imagine a beowulf cluster of F1r5t P05t!
Mwa ha ha!
Oh wait, you mean that I'm too big to be a dragonfly?
Actually the book "The Lost World", which was written by Michael Crichton who wrote "Jurassic Park", shows an opposite behavior of the T-Rex.
The following lines from the book says:
Sarah Harding said, "Why did Dodgson just stand there like that? That's not the way to act around predators. You get caught around lions, you make a lot of noise, wave your hands, throw things at them. Try to scare them off. You don't just stand there."
.....
"Roxton," Levine said, "believed that tyrannosaurs had a visual system like an amphibian: like a frog. A frog sees motion but doesn't see stillness. But it is quite impossible that a predator such as a tyrannosaur would have a visual system that worked that way. Quite impossible. Because the most common defense of prey animals is to freeze. A deer or something like that, it senses danger, and it freezes. A predator has to be able to see them anyway. And of course a tyrannosaur could."
The Picard maneuver. Although I doubt dragonflies can punch it up to warp speed yet.
Yet another example of the universal truth: Everything I need to know, I learned from "The Karate Kid."
-Isaac
I am not a lawyer, and this is not legal advice. For Entertainment Purposes Only.
Boy, that MSNBC article was bad. They even mispelled the researcher's name. It is "Akiko Mizutani" not "Aikiko Mizutani".
Here is some better coverage of the story. discovery, NationalPost, and Ananova.
And here is a nice page from the Insect Vision, Navigation and "Cognition" Laboratory at ANU, but it doesn't cover the dragonfly work.
Since there aren't any deatils.
1. What is are the distances involved?
2. Best guess, they're using a single lens camera. I believe dragonflies eat flies. If this is so and the fact that flies have compound eyes, does this test really hold true for their natural prey or just for 'human-style' eyes?
3. I'm not 100% sure myself that dragonflies have compound eyes, but if they do then I would expect that their eyes are accurate enough to see the retina of it's prey (or whatever) and keep itself in the same position relative to those movments.
BTW these are just the quick thoughts of an amateur scientist with 20 years of software trouble-shooting expereience. The points I've made seem logical to me but I've come to the conclusion that logic really doesn't work that well in the waking world.
The GEEK shall inherit the earth...
Generally speaking, the dragonfly moves in such a way that if you draw a line from the dragonfly to the prey at each increment of some time step, the lines will (nearly, because it's not perfect) cross at one point. Thus, to the prey, it appears that the dragonfly is a stationary object located at the point where the lines cross.
It relies on a lack of depth perception, obviously. As a guess, perhaps the dragonfly is able to accomplish this by using the same visual cues it evokes in its prey - if the dragonfly moves in the right way, then its prey will appear to be a stationary object (from the dragonfly's perspective) as well.
However, this doesn't account for situations where the dragonfly emulates an object that is behind it (i.e., the lines cross at a point on the far side of the dragonfly) or an object at a large distance (where the dragonfly directly shadows the prey, copying its every move).
If you are still confused, think of it this way: You're playing your favorite first-person shooter, and you want to hide behind a tree/pillar/rock so that an approaching target can't see you. You can move around the tree so that it always forms an intervening object. If you draw a line between yourself and your target at each moment in time, they all intersect at the tree. If your target happened to have really crappy eyesight (compound eyes, perhaps) then you could just remove the tree, and at every moment in time they'd see you there along the same line of sight where the tree would have been, so the target perceives you as being located where the tree would have been and moving along as if you were a part of the landscape. (The advantage, though, is that you can move around and close in on your prey, while your prey remains unaware of the soon-to-occur frag.)
So that's why my monitor keeps disappearing if I look at it for more than a few mi... oh...
If you take your finger and hold your eyeball in place things will fade to black (so long as you don't move your head and close the other eye.) I don't think this trick would work against us since we can and do move our eyeballs independently of our body. Fireflies only have to pull this trick on the flies they eat...
The eyemovements we make to be able to sit practically motionless before our monitors is called saccade. (Or "Freedom Eyes" in New American.)
I've seen something like this before. Once I was outside cleaning up after a party. I went to pick up a vase of flowers and I noticed a few tiny fruit flies(?) that were hovering near the flowers. The funny thing was that when I picked up the flowers, these flies would maintain the exact same relative position to the flowers. Even if I rotated the vase around its axis.
It was like taking the flies for a walk on an imaginary but invisible leash.
I guess that the flies had an instinct that to remain still, they must reduce the error in *their* retina between the current background image and the stored background image. I am guessing that dragonflies have evolved to do the same thing but with a greater degree of freedom. i.e. a chosen target rather than the whole background.