ShmoopTube

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[Dino and Coop singing]

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Y'know what helps us unwind after a stressful day?

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Watching a guy in a suit pull hares out of a hat. [Guy in a suit reaches down and pulls hair out of a hat on a couch]

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…Okay, that came out weirder than we thought it would.

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We just meant magic shows.

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But for those days when we just can't get to a magic show, we have something that'll [Guy pulls a rabbit out of a hat]

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take the edge off: optical illusions. [Static on a TV stops and an optical illusion appears]

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To understand what an optical illusion is, it helps to break the term down into smaller [Coop pointing at a blackboard]

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parts.

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The first word, "optical," refers to our eyes.

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The second word, "illusion," means a kind of trick.

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So an optical illusion is a trick involving our eyes. [Dino pointing at a blackboard]

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But who's being tricked, exactly?

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If magic tricks are performed by magicians for audience members… [Magician dancing on stage]

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…are optical illusions performed by eyes, for…other eyes? [Magician disappears in a puff of smoke and only his eyes are left behind]

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We hope not, because we wouldn't want to clean up the seats in a big theatre after a bunch [Angry looking eyes leaving]

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of eyeballs have been sitting in 'em. [Guy cleaning looks grossed out]

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It turns out the sap being tricked in an optical illusion is actually the human brain. [Girls head opens]

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When our eyes look at something…

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…they gather and transmit a whole bunch of information to the brain, with the hope [Girl looking at a globe]

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that the brain will understand what's there. [A globe sign appears in her head]

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So if you look at an apple, your eyes transmit enough visual info to your brain so that it's [Guy looking at an apple on the TV]

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able to think, "Hey look! [Apples going into the guys eyes]

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An apple!" [An apple sign appears in the guys head]

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But with an optical illusion, things aren't quite so simple.

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Our eyes still gather up a bunch of information and transmit that information to the brain. [Optical illusions going into the guys eyes]

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But due to weird uses of color, lights or patterns… [Guy looks shocked]

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…our brain gets confused, and ends up thinking that it sees something different from what's [Two signs appear, faces and vase]

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actually being seen.

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And since brains tend to like getting things right, this can really hurt the brain's self-esteem. [Guy looks angry and storms out]

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We can see how this works with a pretty simple optical illusion.

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Take a look at these two shapes.

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At first glance, it might look like the middle line in A is longer than the one in B. Okay…so

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where's the illusion?

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It turns out that these two middle lines have the exact same length. [Length of line A is copied onto line B to show they are the same length]

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What's especially weird, though, is that even once we know the trick, the two lines still

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look like they're different lengths. [The copied length is taken away]

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The arrangement of the lines create a pattern that our brains just can't help but see incorrectly. [Help me sign on the guys brain]

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It's the sort of trick that might not get you a two-year contract performing magic shows [An explosion goes off and the guy falls over]

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on the Vegas Strip…

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…but hey, at least your brain will always enjoy it. [Guy looks at an optical illusion on the stage and his mind blows up]

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