One of the most disconcerting things about reality is the idea that, just maybe, what we think is “real” actually isn’t.

The idea that we can’t really tell whether what we perceive is true or not is something that every student of philosophy gets hung up about at one time or another- if only because so many philosophers concerned themselves with the problem.  Descartes famously decided that while each of us is really pretty certain that we exist ourselves (“I think therefore I am”) we can’t be as sure about the rest of the world.  In all honesty, how do we prove that we aren’t living amidst the matrix?

But I personally get a little more unnerved when the problem of our perception of the world around us leaves the comfortable fire-side chat world of philosophy and becomes an issue for the scientific community to worry about.  Especially when they start to find out that our brains are lying to us.  And not just every once in a while, but freaking all the time.

Don’t believe me?  Check out the Japanese Science and Technology Agency’s Mind Lab here. The site does an amazing job of illustrating how much of what we perceive is actually just details filled in by our brains in order to allow us to make sense of sensory detail.*

For example, all of our eyes have a blind spot where the optic nerve, the highway that transmits sensory data to the brain, leaves the eye.  Unfortunately this means that there is a small section of the eyeball (corresponding to a section of our field of vision) that doesn’t have light sensors and thus doesn’t receive sensory data. 

Curse you optic nerve!

The size of the spot differs for everyone, but sitting at a normal distance from your computer it measures about the size of bottle cap on your screen.  Think about that for a second.  That is a huge section of your vision that is essentially invisible.

See for yourself.  Cover your left eye and stare at the circle on the left side.  Keep staring at the circle and move your head towards the page and eventually you’ll reach a point where the x on the right disappears. 

How the heck don’t we notice this in everyday life?  Well, part of it is because each of our eyes compensates for the blind spot in the other.  But when that fails the brain is more than happy to try to fill in the details. When you did the previous test, did you notice nothingness where the blind spot occurred?  No, the brain filled in the background, making it appear white. 

Of course that’s a hard thing to tell when the background is just a plain white surface.  But try the same blind spot test with the following images taken from here**, although this time cover your right eye and stare at the shape to the right. 

Interesting, right?  Once you line up the blind spot the brain fills in the details, making the blue line unbroken and filling in the pattern of vertical lines so there’s no blank space (although if your blind spot is big enough the second illusion may be difficult given the size).

So even though in reality there is an empty space in each of those shapes you don’t perceive it.  Rather than leaving you with an uncomfortable nothingness the brain, much like a stressed college student pushed to finish a research paper, fills in the emptiness with bullsh*t. It creates an illusion of a complete and solid sensory experience when it actually knows nothing of the sort.

Freaky, isn’t it?

*Seriously.  Take a couple seconds out of your day and check it out.  It is intriguing and wonderful.   

**This site also brings up the interesting point that the eyes of an octopus don’t have any blind spots at all.  One more reason to fear them.