[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Some vision stuff



I'm branching off from JP, so even if you're sick of THAT subject you
might not mind this cluttering your mailbox... I hope.

Skip Dahlgren <SDAHLGREN@liblan.uams.edu> wrote:

> It should be pointed out, however, that many modern predators are
> more dependent on motion detection than one might think,

I think pretty much all animals with eyes use motion to locate other
living things.  I recently came across a reference (which I'll dig up
again if pressed) which described an experiment conducted on German
shepherds.  The dogs could detect a moving target about twice as far
away as they could detect the same target when it was standing still.
Of course the absolute distances were measured in hundreds of feet (I
guess it was a big target), so don't think you can stand still under a
German shepherd's nose and get away with it.

And "D.W.Naish" <dwn194@soton.ac.uk> writes:

} The T. rex brings her head down to peer into the window and her
} pupil quickly shrinks to a dot (I've tried this on assorted
} livestock and can't get it to work).

Different animals have different degrees of pupillary reflexes, both
in terms of size differences between minimum and maximum constriction,
and in terms of the speed at which the transition can be made.  Our
pupils can change diameter pretty rapidly by a factor of about two or
three, and that's probably what the JP effects people were thinking
when they made the scene.  If you really did try it on livestock
(e.g. sheep, cows and horses), then I'm not surprised that you didn't
see anything so dramatic.  There is a legitimate question to ask as to
whether or not the effect depicted in the movie was reasonable.  I'd
say yes, but with the caveat that I also remember reading (some time
ago, so please don't ask me to track that down!) that the pupillary
size of some birds seems to indicate emotional state moreso than
adaptation state.  Hang out with a parrot for a while and you'll see
what I mean.  If it's a big one, though, I don't recommend you try to
make it angry :-)

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