On Wed, 07 Jul 2004 13:34:02 GMT, John Steinberg wrote:

I have a pet theory that attempts to explain the moon illusion as a
result of the morphology of the human eye/brain combination. It's
still a work in progress (IOW, we're *all* seeing it for the first time
here) but in brief it states that the human visual field was purpose
built and optimized to look straight ahead from an upright position. I
could go on (and on) about why this is so, but since my own eyes are
already glazing over I'll move on to something else.

Cats provide an example of an animal that clearly has a visual system such as
you describe. The receptor rich foveal region (circular in humans) is quite
elongated horizontally, and the retinal and cortical wiring is optimized for
horizontal movement. Cat eyes apparently evolved to serve an animal that hunted
on the plains. The low level visual and cortical structures in humans are
symmetric (not surprising as we evolved from tree dwellers). So if your theory
is correct, I'd have to think the optimization is fairly subtle.

Many optical illusions are based on experience. Some of the more well know ones
involving interactions between straight lines are seen only weakly, or not at
all, by people raised in primitive environments with few linear structures. It
would be interesting to know if there are any such cultural/environmental
influences on the Moon illusion.

BTW, cats also have high density rods and a reflector behind the retina that
greatly increase the quantum efficiency of their eye. Their limiting visual
magnitude is probably close to -10!

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com