Re: motion and vision

[rowe@lepomis.psych.upenn.edu (Mickey Rowe)]

I'm really sorry to let this drift from dinosaurs, but I hate to see
things stated unopposed when I'm fairly well convinced that they are
wrong or oversimplified.

Nicholas Roy Longrich <longrich@phoenix.Princeton.EDU> wrote that a
praying mantis he kept relied on motion to find a grasshopper he fed
it.  I have two responses, a) I too have temporarily housed praying
mantises.  The last one that I had was perfectly willing to eat pieces
of beef heart that I pulled from my freezer (I originally bought the
beef heart for my turtles--honest, you can get the stuff from fish
stores...)  I didn't have to wiggle the beef heart to help him find
it. b) When swatting flies, I use a technique rather similar to that
Nick described for his mantis.  Move towards them while they're
moving, remain motionless as soon as they freeze.  Move closer again
when they start to walk or clean themselves. Stop if they stop.  You
can almost always catch flies this way.  I suspect mantises also have
learned (via more hard-wired pathways, than what I use :-) that this
is an effective strategy to pursue while stalking other insects.

> Now, the interesting part is that the mantis, instead of moving in a
> direct, fluid manner towards its prey, would move in fits and
> starts, jerking towards and away while slowly creeping up on the
> grasshoper.

I don't know where you heard the story about that behaviour being an
attempt at deception -- it's well documented that mantises perform
these motions in order to gain distance cues.  They rely on motion
parallax to tell them whether an object is near or far.  Usually the
motions are combined with side to side movements, though.  The mantis
"knows" that when it wobbles, objects which appear to move quickly are
closer than those that appear to move slowly.

In a related thread Tim Madden <TMADDEN@medicode.mhs.compuserve.com>
disagrees that cats prefer horizontal movements.  I once saw an
episode of Nature devoted to cats, and it was stated there that cats
do preferentially react to horizontal movements.  That doesn't mean
they can't see vertical movements, but they don't attend to them as
much (without training anyways).

And on a completely different topic, Bonnie Blackwell
<bonn@qcvaxa.acc.qc.edu> writes:

: One of the reasons Star Trek is relatively error free is that they
: have always maintained a stable of JPL and NASA advisors who help
: them get it right.

Aaaaa-aaack!  I've often wondered what those advisors do, because Star
Trek is ABYSMAL when it comes to its "science".  If you want to see a
show that does a better job on that end, watch "Babylon 5".

Ok, I think I'm done for today.

-- 
Mickey Rowe     (rowe@lepomis.psych.upenn.edu)