 |
 |
Most fascinating. Thanks, Ray Moneesha 2008/8/31 rayilynlee <[log in to unmask]> > Study says eyes evolved for X-Ray vision > August 29, 2008 > > Troy, N.Y. - The advantage of using two eyes to see the world around us has > long been associated solely with our capacity to see in 3-D. Now, a new > study from a scientist at Rensselaer Polytechnic Institute has uncovered a > truly eye-opening advantage to binocular vision: our ability to see through > things. > > Most animals - fish, insects, reptiles, birds, rabbits, and horses, for > example - exist in non-cluttered environments like fields or plains, and > they have eyes located on either side of their head. These sideways-facing > eyes allow an animal to see in front of and behind itself, an ability also > known as panoramic vision. > > Humans and other large mammals - primates and large carnivores like tigers, > for example - exist in cluttered environments like forests or jungles, and > their eyes have evolved to point in the same direction. While animals with > forward-facing eyes lose the ability to see what's behind them, they gain > X-ray vision, according to Mark Changizi, assistant professor of cognitive > science at Rensselaer, who says eyes facing the same direction have been > selected for maximizing our ability to see in leafy environments like > forests. > > All animals have a binocular region - parts of the world that both eyes can > see simultaneously - which allows for X-ray vision and grows as eyes become > more forward facing. > > Demonstrating our X-ray ability is fairly simple: hold a pen vertically and > look at something far beyond it. If you first close one eye, and then the > other, you'll see that in each case the pen blocks your view. If you open > both eyes, however, you can see through the pen to the world behind it. > > To demonstrate how our eyes allow us to see through clutter, hold up all of > your fingers in random directions, and note how much of the world you can > see beyond them when only one eye is open compared to both. You miss out on > a lot with only one eye open, but can see nearly everything behind the > clutter with both. > > "Our binocular region is a kind of 'spotlight' shining through the clutter, > allowing us to visually sweep out a cluttered region to recognize the > objects beyond it," says Changizi, who is principal investigator on the > project. "As long as the separation between our eyes is wider than the width > of the objects causing clutter - as is the case with our fingers, or would > be the case with the leaves in the forest - then we can tend to see through > it." > > To identify which animals have this impressive power, Changizi studied 319 > species across 17 mammalian orders and discovered that eye position depends > on two variables: the clutter, or lack thereof in an animal's environment, > and the animal's body size relative to the objects creating the clutter. > > Changizi discovered that animals in non-cluttered environments - which he > described as either "non-leafy surroundings, or surroundings where the > cluttering objects are bigger in size than the separation between the > animal's eyes" (think a tiny mouse trying to see through 6-inch wide leaves > in the forest) - tended to have sideways-facing eyes. > > "Animals outside of leafy environments do not have to deal with clutter no > matter how big or small they are, so there is never any X-ray advantage to > forward-facing eyes for them," says Changizi. "Because binocular vision does > not help them see any better than monocular vision, they are able to survey > a much greater region with sideways-facing eyes." > > However, in cluttered environments - which Changizi defined as leafy > surroundings where the cluttering objects are smaller than the separation > between an animal's eyes - animals tend to have a wide field of binocular > vision, and thus forward-facing eyes, in order to see past leaf walls. > > "This X-ray vision makes it possible for animals with forward-facing eyes > to visually survey a much greater region around themselves than > sideways-facing eyes would allow," says Changizi. "Additionally, the larger > the animal in a cluttered environment, the more forward facing its eyes will > be to allow for the greatest X-ray vision possible, in order to aid in > hunting, running from predators, and maneuvering through dense forest or > jungle." > > Changizi says human eyes have evolved to be forward facing, but that we now > live in a non-cluttered environment where we might actually benefit more > from sideways-facing eyes. > > "In today's world, humans have more in common visually with tiny mice in a > forest than with a large animal in the jungle. We aren't faced with a great > deal of small clutter, and the things that do clutter our visual field - > cars and skyscrapers - are much wider than the separation between our eyes, > so we can't use our X-ray power to see through them," Changizi says. "If we > froze ourselves today and woke up a million years from now, it's possible > that it might be difficult for us to look the new human population in the > eyes, because by then they might be facing sideways." > > Rensselaer Polytechnic Institute > > > Rayilyn Brown > Director AZNPF > Arizona Chapter National Parkinson Foundation > [log in to unmask] > ---------------------------------------------------------------------- > To sign-off Parkinsn send a message to: mailto: > [log in to unmask] > In the body of the message put: signoff parkinsn > ---------------------------------------------------------------------- To sign-off Parkinsn send a message to: mailto:[log in to unmask] In the body of the message put: signoff parkinsn