Why don't you usually see your nose?

Close one eye, and focus straight ahead, without moving your eyes. You'll notice a fleshy blur in your peripheral vision — your nose. It's there every waking moment, yet you're hardly ever aware of it. So why can't we see our noses, even though they're literally right in front of us?

"You can see your nose," said Michael Webster, a vision scientist and co-director of the neuroscience program at the University of Nevada, Reno. We’re just not aware of it most of the time.

The main reason our noses don't take up space in our vision comes down to a somewhat startling fact: We don't see the world as it is but rather as a model our brains have constructed to help us survive.

"Vision is actually a prediction about what you think the world is," Webster said. "You want to be aware of, 'How does the world differ?' 'What are the surprises and errors and the things that I didn't predict?' Normally, you're not aware of your nose because you already know about it and you just don't want to be aware of it. … It's a big disadvantage to waste some of your energy attending to that."

This makes sense from a survival perspective; constantly processing unchanging features, like your nose, would be a waste of limited mental resources when you need to detect threats, find food or navigate your environment. In fact, your brain cancels out all sorts of information about your own body to help you perceive the outside world.

Take your eyes’ blood vessels, for example. The photoreceptors that collect light from the outside world are located in the back of the eye, behind a tangle of blood vessels.

"It's like you're sitting up in a tree of dead branches and you're actually seeing the world through all these dead branches," Webster said.

Your brain usually cancels that out, but there are ways to make your eye's blood vessels appear so your conscious mind can see them. If you’ve ever had an eye exam, you might have noticed dark squiggles in your vision when the optometrist passed a light across your eye. Those are the shadows cast by your eyes’ blood vessels.

Your brain doesn’t just cancel out unwanted information — sometimes it creates information from scratch. Take your blind spot: the blank region in your vision that corresponds to where the optic nerve leaves the eye. Your blind spot is about 5 degrees wide, or more than twice the size of the full moon's appearance in the sky. Yet we usually aren't aware of this huge gap in our vision.

"We're actually filling in that information," Webster said. "Instead of seeing the absence, we've got clues from what's around the blind spot telling us, 'OK, if I'm looking at a white piece of paper, it's very likely that the part that's in the blind spot is also white.'"

It's even easier to perceive your nose — in fact, you might be hyperaware of it right now simply because you're thinking about it.

" If you actually are consciously trying to see something, then you do become aware of it," Webster said.

Our "disappearing" noses reveal something profound about how we experience reality: Our vision isn't like a camera recording what's really there; it's more akin to an artist creating a model of the world that's most useful to us.

Webster took this idea even further. We may not perceive reality at all. "Even this model itself is really just the information that you need to get by. It's not really telling you what the reality of the world is."