I “See”, Said the Brain

Do You Believe That Vision Is Your Most Important Sense? Then You Need To Learn How to Protect Your EyeSight.
By: Bill Coughlin
 
Nov. 20, 2009 - PRLog -- You understand that we have two eyes sending billions of electrical bits through the optic nerve to the visual cortex of the brain. This is where the ultimate action takes place. Somehow (and researchers are slowly beginning to unravel the mystery), the brain interprets these signals into a stable, colorful, three-dimensional world out there.

You realize, of course, that the brain does not actually “see” the tiny, two-dimensional, upside-down, distorted and constantly shifting image on the retina. No light reaches the brain at all; it only receives patterns of nerve impulses from which meaning must be rendered. We usually do this so effortlessly that the very complicated nature of the process is difficult to appreciate and decipher.

The fact that the image on the retina is upside-down seems to puzzle some people as to why we don’t see that way. But remember the brain is not looking at the retina. It constructs the visual world so that down is where you feet are normally planted, up is towards the sky within a general frame of reference. If you stand on your head, the scene looks “unusual” but the chair is not standing on the ceiling.

A more difficult idea to reconcile is that the eyes are in constant motion, yet we see the world as a stable entity. The eyes continuously jump about, quickly shifting from one location to another in fractions of second, ballistic hops called saccades.

How can the brain get any meaning from a perpetually changing image on the retina? You will find all these answers at http://www.protect-your-eyesight.com


Surprisingly, the changes are necessary for vision. The cells in the retina and visual system respond best to changes with a rich outpouring of signals – changes in brightness, color, texture, orientation, etc. Without these changes, there would be not vision!

Try this experiment. Stare at any object and make a mighty effort to keep your eyes perfectly still. It’s very difficult to do, but if you can manage it you’ll notice that parts of the scene begin to fade away. Chances are you’ll make an involuntary, slight eye movement because the brain will not easily tolerate loss of vision.

Each eye sends a separate image to the brain, but you usually see only one object.

Want to see more?

Hold you thumb up at arms length and sight across it at a distance object with both eyes open. You not only see two thumbs, one from each eye, but also the single image of the distant object.

What’s going on?

The answer is tied up with the essence of depth perception. There are special brain cells, which have the ability to combine similar objects located within a limited, prescribed range of the two eyes into one percept. When this is achieved, the individual images are squelched. In the above experiment your thumb images are outside the operating range of these cells.

So far we’ve been discussing looking at still life objects. Suppose we now complicate mattes by having the object move. The images flit around on the retina just as they do when the eyes move.

How does the brain know the difference?

Assume you’re riding on a train. How does the brain decide if the telephone poles are moving or if you’re moving? In all such instances the brain must also factor imputes from other sources such as the neck muscles, legs, etc., then make a reasonable guess base on past experience. Most of the time the decision is correct, but sometimes the brain is fooled in a visual illusion. You’re on a train in a station next to another train. The other starts to move and you’re convinced yours is moving.

This gives you some flavor (albeit, minor) of the complicated wordings that go on in the visual system before the brain can say; “I SEE!” http://www.protect-your-eyesight.com

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What we feed our bodies feeds our eyes. Many of the vitamins and minerals in our bodies are found in much higher concentrations in our eyes, so a diet lacking in these vitamins and minerals can lead to vision problems as we grow older.
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