Something that always baffled me was how the brain can turn the two slightly different images received from both eyes into one single image. How does the brain deal with this?

We tend to think of our eyes as two video cameras, sending two overlapping images to the brain where vision is passively perceived. But human vision is different from video cameras in many important ways -and it is not a passive process.

The image each eye sees is actually upside-down and right-for-left. That inverted image is already being broken down into its component parts well before it reaches the visual part of the brain (the occipital cortex). These visual components are then knitted together by the brain into a single, fused virtual image that is projected onto the world "out there." That virtual image corresponds pretty well with what is actually "out there" but it is definitely not the same thing. What we see is heavily influenced by what interests us, what we are afraid of, and what we expect to see.

This explanation may seem weird at first because it is so counter-intuitive. But it is a more accurate description of how we see.

_Written by J. Trevor Woodhams, M.D. - Chief of Surgery, Woodhams Eye Clinic