Did you know that your two eyes do not see the same image? Cover one eye at a time and you'll see the difference. It's subtle but important. The similar-yet-distinct images are integrated in the brain and this visual fusion is responsible for depth perception and stereopsis.
Why is it that wearing glasses with one yellow lens and one blue lens will not create a world of green? This is the kind of question vision researchers from UC San Diego are trying to answer.
At any instant the brain decides to accept one image or the other, never both.
Retinal rivalry is the explanation for the brain's inability to fuse two different visual images. This phenomenon also occurs in the tangible world. If you hold an apple with both hands you don't feel two apples, do you?
Understanding the phenomenon of retinal rivalry has provided great insights regarding visual changes in stroke victims and for patients with Crooked Eyes.
Want to learn more? Direct both of your eyes to the recent issue of Scientific American Mind cited below.
REFERENCE: Scientific American Mind (Dec06/Jan07) 'When the Two Eyes Clash'. pages 16-18.