Re: motion and vision

[Lars_Bergquist@public.se (Lars Bergquist)]

On 95-02-28 at 05.48, longrich@phoenix.Princeton.EDU wrote:

> When the grasshopper stopped, the 
> mantis stood still and stopped moving towards it. When the 
> grasshopper resumed motion, the mantis struck and began to eat. I 
> wouldn't discount shape as having some role here, but I'd guess that 
> motion was the primary means by which my pet tracked its prey.

There seems to exist some kind of evolution in the direction of more
analysis of form and less dependence on object motion. Image analysis
is of course very advanced stuff--no one has found out a way yet to
make a missile seeker that can reliably identify a motionless tank, 
say. They all make use of quite simplistic heat or microwave 
"signatures" and it therefore not difficult to deceive them. And even
in man, it is my experience (mostly from my sniper training) that
you can radically diminish the chances of being discovered just by
keeping completely immobile. Once I waited out an advancing platoon
at the edge of a little woods, without any fancy camouflage at all, and
they did not observe me until I opened fire at thirty meters or so!

Here, by the way, is an interesting tidbit: Swedish researchers have
found that vole urine is strongly visible in the ultraviolet. The voles
use urine to mark territory and their most-used paths. It was also
found that hawks see further into the UV than we do (we have a pretty
abrupt cut-off at around 380--400 nm) and can see these tracks.
This is good for the hawks but bad news for the voles!

Lars Bergquist
lars_bergquist@public.se
(lexicographer ... "a harmless drudge" according to Dr. Johnson,
so bear with me)

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