When vision is lost, a person’s senses of touch and hearing become enhanced. But exactly how this happens has been unclear. And why do we have two eyes that face forward, rather than eyes on the sides of heads, the way most animals do?

Complete loss of vision leads to profound changes in the visual cortex of the brain. Researcher Alvaro Pascual-Leone says, “In our studies [in which a group of sighted study subjects were blindfolded for five days], we have shown that even in an adult, the normally developed visual system quickly becomes engaged to process touch in response to complete loss of sight.”

Researchers found that the subjects who were blindfolded were superior at learning Braille than their non-blindfolded counterparts. Furthermore, the brain scans of the blindfolded subjects showed that the brain?s visual cortex had become extremely active in response to touch (in contrast to the initial scan in which there was little or no activity). Twenty-four hours after the blindfolds were removed, and the subjects were re-scanned, it was discovered that their visual cortices were no longer responsive to tactile stimulation.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 has another 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 what scientists call “X-ray vision.”

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.

Researcher Mark Changizi says, “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.”

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. Changizi says, “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. 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”?Or would they be big and black?Art credit: freeimages.co.uk

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