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  • I want to start with a game. Okay?

  • And to win this game,

  • all you have to do is see the reality that's in front of you

  • as it really is, all right?

  • So we have two panels here, of colored dots.

  • And one of those dots is the same in the two panels.

  • And you have to tell me which one.

  • Now, I narrowed it down

  • to the gray one, the green one, and, say, the orange one.

  • So by a show of hands, we'll start with the easiest one.

  • Show of hands: how many people think it's the gray one?

  • Really? Okay.

  • How many people think it's the green one?

  • And how many people think it's the orange one?

  • Pretty even split.

  • Let's find out what the reality is.

  • Here is the orange one.

  • (Laughter)

  • Here is the green one.

  • And here is the gray one.

  • (Laughter)

  • So for all of you who saw that, you're complete realists.

  • All right?

  • (Laughter)

  • So this is pretty amazing, isn't it?

  • Because nearly every living system

  • has evolved the ability to detect light in one way or another.

  • So for us, seeing color

  • is one of the simplest things the brain does.

  • And yet, even at this most fundamental level,

  • context is everything.

  • What I'm going to talk about is not that context is everything,

  • but why context is everything.

  • Because it's answering that question

  • that tells us not only why we see what we do,

  • but who we are as individuals,

  • and who we are as a society.

  • But first, we have to ask another question,

  • which is, "What is color for?"

  • And instead of telling you, I'll just show you.

  • What you see here is a jungle scene,

  • and you see the surfaces according to the amount of light

  • that those surfaces reflect.

  • Now, can any of you see the predator that's about to jump out at you?

  • And if you haven't seen it yet, you're dead, right?

  • (Laughter)

  • Can anyone see it? Anyone? No?

  • Now let's see the surfaces

  • according to the quality of light that they reflect.

  • And now you see it.

  • So, color enables us to see

  • the similarities and differences between surfaces,

  • according to the full spectrum of light that they reflect.

  • But what you've just done

  • is in many respects mathematically impossible.

  • Why?

  • Because, as Berkeley tells us,

  • we have no direct access to our physical world,

  • other than through our senses.

  • And the light that falls onto our eyes

  • is determined by multiple things in the world,

  • not only the color of objects,

  • but also the color of their illumination,

  • and the color of the space between us and those objects.

  • You vary any one of those parameters,

  • and you'll change the color of the light that falls onto your eye.

  • This is a huge problem,

  • because it means that the same image

  • could have an infinite number of possible real-world sources.

  • Let me show you what I mean.

  • Imagine that this is the back of your eye, okay?

  • And these are two projections from the world.

  • They're identical in every single way.

  • Identical in shape, size, spectral content.

  • They are the same, as far as your eye is concerned.

  • And yet they come from completely different sources.

  • The one on the right comes from a yellow surface,

  • in shadow, oriented facing the left,

  • viewed through a pinkish medium.

  • The one on the left comes from an orange surface,

  • under direct light, facing to the right,

  • viewed through sort of a bluish medium.

  • Completely different meanings,

  • giving rise to the exact same retinal information.

  • And yet it's only the retinal information that we get.

  • So how on Earth do we even see?

  • So if you remember anything in this next 18 minutes,

  • remember this:

  • that the light that falls onto your eye,

  • sensory information, is meaningless,

  • because it could mean literally anything.

  • And what's true for sensory information is true for information generally.

  • There's no inherent meaning in information.

  • It's what we do with that information that matters.

  • So, how do we see? Well, we see by learning to see.

  • The brain evolved the mechanisms for finding patterns,

  • finding relationships in information,

  • and associating those relationships with a behavioral meaning,

  • a significance, by interacting with the world.

  • We're very aware of this

  • in the form of more cognitive attributes, like language.

  • I'm going to give you some letter strings,

  • and I want you to read them out for me, if you can.

  • Audience: "Can you read this?"

  • "You are not reading this."

  • "What are you reading?"

  • Beau Lotto: "What are you reading?" Half the letters are missing, right?

  • There's no a priori reason

  • why an "H" has to go between that "W" and "A."

  • But you put one there. Why?

  • Because in the statistics of your past experience,

  • it would have been useful to do so.

  • So you do so again.

  • And yet you don't put a letter after that first "T."

  • Why? Because it wouldn't have been useful in the past.

  • So you don't do it again.

  • So, let me show you how quickly our brains can redefine normality,

  • even at the simplest thing the brain does, which is color.

  • So if I could have the lights down up here.

  • I want you to first notice that those two desert scenes are physically the same.

  • One is simply the flipping of the other.

  • Now I want you to look at that dot

  • between the green and the red.

  • And I want you to stare at that dot. Don't look anywhere else.

  • We're going to look at it for about 30 seconds,

  • which is a bit of a killer in an 18-minute talk.

  • (Laughter)

  • But I really want you to learn.

  • And I'll tell you -- don't look anywhere else --

  • I'll tell you what's happening in your head.

  • Your brain is learning,

  • and it's learning that the right side of its visual field

  • is under red illumination;

  • the left side of its visual field is under green illumination.

  • That's what it's learning. Okay?

  • Now, when I tell you, I want you to look at the dot between the two desert scenes.

  • So why don't you do that now?

  • (Laughter)

  • Can I have the lights up again?

  • I take it from your response they don't look the same anymore, right?

  • (Applause)

  • Why? Because your brain is seeing that same information

  • as if the right one is still under red light,

  • and the left one is still under green light.

  • That's your new normal.

  • Okay? So, what does this mean for context?

  • It means I can take two identical squares,

  • put them in light and dark surrounds,

  • and the one on the dark surround looks lighter than on the light surround.

  • What's significant is not simply the light and dark surrounds that matter.

  • It's what those light and dark surrounds meant for your behavior in the past.

  • So I'll show you what I mean.

  • Here we have that exact same illusion.

  • We have two identical tiles on the left,

  • one in a dark surround, one in a light surround.

  • And the same thing over on the right.

  • Now, I'll reveal those two scenes,

  • but I'm not going to change anything within those boxes,

  • except their meaning.

  • And see what happens to your perception.

  • Notice that on the left

  • the two tiles look nearly completely opposite:

  • one very white and one very dark, right?

  • Whereas on the right, the two tiles look nearly the same.

  • And yet there is still one on a dark surround,

  • and one on a light surround.

  • Why?

  • Because if the tile in that shadow were in fact in shadow,

  • and reflecting the same amount of light to your eye

  • as the one outside the shadow,

  • it would have to be more reflective -- just the laws of physics.

  • So you see it that way.

  • Whereas on the right, the information is consistent

  • with those two tiles being under the same light.

  • If they're under the same light reflecting the same amount of light to your eye,

  • then they must be equally reflective.

  • So you see it that way.

  • Which means we can bring all this information together

  • to create some incredibly strong illusions.

  • This is one I made a few years ago.

  • And you'll notice you see a dark brown tile at the top,

  • and a bright orange tile at the side.

  • That is your perceptual reality.

  • The physical reality is that those two tiles are the same.

  • Here you see four gray tiles on your left,

  • seven gray tiles on the right.

  • I'm not going to change those tiles at all,

  • but I'm going to reveal the rest of the scene.

  • And see what happens to your perception.

  • The four blue tiles on the left are gray.

  • The seven yellow tiles on the right are also gray.

  • They are the same. Okay?

  • Don't believe me? Let's watch it again.

  • What's true for color is also true for complex perceptions of motion.

  • So, here we have --

  • let's turn this around -- a diamond.

  • And what I'm going to do is, I'm going to hold it here,

  • and I'm going to spin it.

  • And for all of you, you'll see it probably spinning this direction.

  • Now I want you to keep looking at it.

  • Move your eyes around, blink, maybe close one eye.

  • And suddenly it will flip, and start spinning the opposite direction.

  • Yes? Raise your hand if you got that. Yes?

  • Keep blinking.

  • Every time you blink, it will switch.

  • So I can ask you, which direction is it rotating?

  • How do you know?

  • Your brain doesn't know, because both are equally likely.

  • So depending on where it looks,

  • it flips between the two possibilities.

  • Are we the only ones that see illusions?

  • The answer to this question is no.

  • Even the beautiful bumblebee,

  • with its mere one million brain cells,

  • which is 250 times fewer cells than you have in one retina,

  • sees illusions, does the most complicated things

  • that even our most sophisticated computers can't do.

  • So in my lab we work on bumblebees,

  • because we can completely control their experience,

  • and see how it alters the architecture of their brain.

  • We do this in what we call the Bee Matrix.

  • Here you have the hive.

  • You can see the queen bee, the large bee in the middle.

  • Those are her daughters, the eggs.

  • They go back and forth between this hive and the arena, via this tube.

  • You'll see one of the bees come out here.

  • You see how she has a little number on her?

  • There's another one coming out, she also has a number on her.

  • Now, they're not born that way, right?

  • We pull them out, put them in the fridge, and they fall asleep.

  • Then you can superglue little numbers on them.

  • (Laughter)

  • And now, in this experiment they get a reward if they go to the blue flowers.

  • They land on the flower,

  • stick their tongue in there, called a proboscis, and drink sugar water.

  • She's drinking a glass of water that's about that big to you and I,

  • will do that about three times, then fly.

  • And sometimes they learn not to go to the blue,

  • but to go where the other bees go.

  • So they copy each other.

  • They can count to five. They can recognize faces.

  • And here she comes down the ladder.

  • And she'll come into the hive, find an empty honey pot,

  • and throw up, and that's honey.

  • (Laughter)

  • Now remember, she's supposed to be going to the blue flowers,

  • but what are these bees doing in the upper right corner?

  • It looks like they're going to green flowers.

  • Now, are they getting it wrong?

  • And the answer to the question is no. Those are actually blue flowers.

  • But those are blue flowers under green light.

  • So they're using the relationships between the colors to solve the puzzle,

  • which is exactly what we do.