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We think the input of our senses is real. We are sure that we see exactly what we see, that it’s an accurate picture of whatever we’re looking at. We assume the same about taste, smell and touch.

But have you ever touched ice and felt it burn as if it were hot? Or touched something hot for an instant and couldn’t tell if it was really cold? There is an instant, just an instant, where the brain takes a moment to ponder a sensory input and then interpret it. It is our brain, not our nerves, that is telling us what a stimulus is.

One of the ways neurologists test our responses is not to let us see what they are doing and then ask what we feel. When you go through those tests, you find that there is a moment where, without the confirmation of vision, you wonder. Hot/cold, sharp/dull?

With vision, as I’ve learned over the last few days, and from studies I made years ago, our brains do most of the work. We have rods and cones in the eye, a pixelated version of what we see. The brain fills in the gaps.

For example, you can’t see the blind spot in your eye unless you go looking for it by covering one eye and moving something around until you hit the place where none of us has any vision. It’s rather startling, because as we go about our days we do not notice that we have that blind spot. The brain smooths it over for us.

The fact that vision is built in our brains is the reason we can wear glasses. Glasses actually cause a warping of the light coming in. Depending on the strength of the prescription, the warping will be more or less. For a brief time after getting a prescription change, you will notice that straight lines bend.

Ah, but the brain is wired to see straight lines. Hard-wired. So in no time at all, those lines get straight again, even though our eyes are seeing them curved.

I have a huge scotoma (a blind spot) in my left eye, and have had it since at least childhood. It might as well not be there until someone tests me for it. Only then do I noticed that a huge chunk of my visual field is not even there.

As I adapt to the recent changes in my vision, I am reminded of how large a part the brain plays in our perception of reality. It fills in blanks. It makes judgments of what we are seeing, feeling and smelling. As long as those judgments are reasonably correct, we’re okay.

But just imagine if they go awry.

So how do we know what is real? Our brains tell us. They create our reality from the incoming bits of information. The pixels of the world around us.

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