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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.
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.
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.)