This is an image of a young woman with a feathered hat looking over her shoulder.

Or... is it?

Her chin also makes out the nose of an old woman, looking down.

And take this image of a vase.

Is it a vase?

It's also the outline of two faces.

These perceptual illusions are called ambiguous figures, because they cause you to switch between more than one way of viewing an object.

And there's one type of visual phenomena that's a lot weirder - personally it's my favourite.

And to experience it, I'm going to show you how to see through a hole in your hand, just by using a piece of paper.

It's really, really simple!

Start with a piece of paper or even a bank note and roll it up into a tube- it's important to keep the tube narrow.

Put that tube right up to your eye and look through it.

Then place your other hand right against the piece of paper, about 2 inches or 5 centimetres away from your face.

Keep your hand there and look into the distance, through the tube and don't focus on your other hand.

Give it a little bit of time, like at least 10 seconds of looking down the tube.

What you can see seems like your field of vision merging; so you can see a hole in your hand, the hole being the middle of that tube you're holding.

It's weird, right?

So what's going on?

Well, two different images are being shown to each of your eyes.

If your brain can't combine these two images, it just suppresses the image in one eye, and your other eye becomes more dominant.

In this case, your hand will generally stay suppressed from your awareness because it's the weaker stimulus.

This phenomenon is known as binocular rivalry.

And A number of brain areas and operations are involved in binocular rivalry, including what's going on in your visual pathway.

The brain cells or neurons in the early stages of your visual processing respond to the physical stimulus of each eye, but then neurons in later stages of visual processing can be switched on and off and cause the alternations.

Researchers think the signals with one of the stimuli are suppressed somewhere between these stages, as if there's a gate to visual consciousness that some signals open first.

You don't normally notice this dominance and suppression in your eyes because they rarely stay fixed on one thing for more than a few hundred milliseconds.

For me, what makes binocular rivalry so amazing is that your perceptual experience changes while the physical stimulus you're seeing remains the same.

The input from your eyes is constant - the difference takes place in your brain.

Of all the ways you can trick your brain, this is an awesome one to show people because you can turn your hand into anything at the dinner table.

Velociraptor hand!

See you next week.

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