RE: Bird (Dinosaur?) vision

[Jeff Hecht <jeff@jeffhecht.com>]

At 10:08 PM -0700 7/22/04, Eric Martichuski wrote:
> > From: Lawrence_Dunn@smbcgroup.com
> > Is it true that some birds can see only movement -- that they cannot "see"
> > something that is not moving?  I've recently had this suggested to me, but
> > I'm not sure I see the sense of it.  Is there such a condition in nature?
> > If so, what is it called?
>
> I'm skeptical about this condition existing in birds, but I have 
> read that it exists in frogs.  The sense of it is probably that, if 
> you don't have a lot of brain-power to spare, the really _vital_ 
> things for you to see are almost always going to be the moving 
> ones...especially if you eat insects and not plants.
>
> And it's probably not a case of absolute stillness = invisibility 
> either, just an extreme loss of definition.

Vision is a complex process and involves the brain as well as the 
light detectors on the retina. Some seem to be 'wired up' to detect 
motion, presumably by recognizing change in the illumination of 
certain parts of the retina. We use this effect ourselves; our brains 
alert us to motion and our eye almost instinctively turns toward the 
spot of motion. In that way, motion catches our eye, but it isn't all 
that we see. Presumably there is considerable variation in what other 
species look for and what catches their eyes. -- Jeff Hecht