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  • I love a great mystery,

  • and I'm fascinated by the greatest unsolved mystery in science,

  • perhaps because it's personal.

  • It's about who we are,

  • and I can't help but be curious.

  • The mystery is this:

  • What is the relationship between your brain

  • and your conscious experiences,

  • such as your experience of the taste of chocolate

  • or the feeling of velvet?

  • Now, this mystery is not new.

  • In 1868, Thomas Huxley wrote,

  • "How it is that anything so remarkable as a state of consciousness comes about

  • as the result of irritating nervous tissue

  • is just as unaccountable

  • as the appearance of the genie when Aladdin rubbed his lamp."

  • Now, Huxley knew that brain activity

  • and conscious experiences are correlated,

  • but he didn't know why.

  • To the science of his day, it was a mystery.

  • In the years since Huxley,

  • science has learned a lot about brain activity,

  • but the relationship between brain activity

  • and conscious experiences is still a mystery.

  • Why? Why have we made so little progress?

  • Well, some experts think that we can't solve this problem

  • because we lack the necessary concepts and intelligence.

  • We don't expect monkeys to solve problems in quantum mechanics,

  • and as it happens, we can't expect our species to solve this problem either.

  • Well, I disagree. I'm more optimistic.

  • I think we've simply made a false assumption.

  • Once we fix it, we just might solve this problem.

  • Today, I'd like tell you what that assumption is,

  • why it's false, and how to fix it.

  • Let's begin with a question:

  • Do we see reality as it is?

  • I open my eyes

  • and I have an experience that I describe as a red tomato a meter away.

  • As a result, I come to believe that in reality,

  • there's a red tomato a meter away.

  • I then close my eyes, and my experience changes to a gray field,

  • but is it still the case that in reality, there's a red tomato a meter away?

  • I think so, but could I be wrong?

  • Could I be misinterpreting the nature of my perceptions?

  • We have misinterpreted our perceptions before.

  • We used to think the Earth is flat, because it looks that way.

  • Pythagorus discovered that we were wrong.

  • Then we thought that the Earth is the unmoving center of the Universe,

  • again because it looks that way.

  • Copernicus and Galileo discovered, again, that we were wrong.

  • Galileo then wondered if we might be misinterpreting our experiences

  • in other ways.

  • He wrote: "I think that tastes, odors, colors, and so on

  • reside in consciousness.

  • Hence if the living creature were removed, all these qualities would be annihilated."

  • Now, that's a stunning claim.

  • Could Galileo be right?

  • Could we really be misinterpreting our experiences that badly?

  • What does modern science have to say about this?

  • Well, neuroscientists tell us that about a third of the brain's cortex

  • is engaged in vision.

  • When you simply open your eyes and look about this room,

  • billions of neurons and trillions of synapses are engaged.

  • Now, this is a bit surprising,

  • because to the extent that we think about vision at all,

  • we think of it as like a camera.

  • It just takes a picture of objective reality as it is.

  • Now, there is a part of vision that's like a camera:

  • the eye has a lens that focuses an image on the back of the eye

  • where there are 130 million photoreceptors,

  • so the eye is like a 130-megapixel camera.

  • But that doesn't explain the billions of neurons

  • and trillions of synapses that are engaged in vision.

  • What are these neurons up to?

  • Well, neuroscientists tell us that they are creating, in real time,

  • all the shapes, objects, colors, and motions that we see.

  • It feels like we're just taking a snapshot of this room the way it is,

  • but in fact, we're constructing everything that we see.

  • We don't construct the whole world at once.

  • We construct what we need in the moment.

  • Now, there are many demonstrations that are quite compelling

  • that we construct what we see.

  • I'll just show you two.

  • In this example, you see some red discs with bits cut out of them,

  • but if I just rotate the disks a little bit,

  • suddenly, you see a 3D cube pop out of the screen.

  • Now, the screen of course is flat,

  • so the three-dimensional cube that you're experiencing

  • must be your construction.

  • In this next example,

  • you see glowing blue bars with pretty sharp edges

  • moving across a field of dots.

  • In fact, no dots move.

  • All I'm doing from frame to frame is changing the colors of dots

  • from blue to black or black to blue.

  • But when I do this quickly,

  • your visual system creates the glowing blue bars

  • with the sharp edges and the motion.

  • There are many more examples, but these are just two

  • that you construct what you see.

  • But neuroscientists go further.

  • They say that we reconstruct reality.

  • So, when I have an experience that I describe as a red tomato,

  • that experience is actually an accurate reconstruction

  • of the properties of a real red tomato

  • that would exist even if I weren't looking.

  • Now, why would neuroscientists say that we don't just construct,

  • we reconstruct?

  • Well, the standard argument given

  • is usually an evolutionary one.

  • Those of our ancestors who saw more accurately

  • had a competitive advantage compared to those who saw less accurately,

  • and therefore they were more likely to pass on their genes.

  • We are the offspring of those who saw more accurately,

  • and so we can be confident that, in the normal case,

  • our perceptions are accurate.

  • You see this in the standard textbooks.

  • One textbook says, for example,

  • "Evolutionarily speaking,

  • vision is useful precisely because it is so accurate."

  • So the idea is that accurate perceptions are fitter perceptions.

  • They give you a survival advantage.

  • Now, is this correct?

  • Is this the right interpretation of evolutionary theory?

  • Well, let's first look at a couple of examples in nature.

  • The Australian jewel beetle

  • is dimpled, glossy and brown.

  • The female is flightless.

  • The male flies, looking, of course, for a hot female.

  • When he finds one, he alights and mates.

  • There's another species in the outback,

  • Homo sapiens.

  • The male of this species has a massive brain

  • that he uses to hunt for cold beer.

  • (Laughter)

  • And when he finds one, he drains it,

  • and sometimes throws the bottle into the outback.

  • Now, as it happens, these bottles are dimpled, glossy,

  • and just the right shade of brown to tickle the fancy of these beetles.

  • The males swarm all over the bottles trying to mate.

  • They lose all interest in the real females.

  • Classic case of the male leaving the female for the bottle.

  • (Laughter) (Applause)

  • The species almost went extinct.

  • Australia had to change its bottles to save its beetles.

  • (Laughter)

  • Now, the males had successfully found females for thousands,

  • perhaps millions of years.

  • It looked like they saw reality as it is, but apparently not.

  • Evolution had given them a hack.

  • A female is anything dimpled, glossy and brown,

  • the bigger the better.

  • (Laughter)

  • Even when crawling all over the bottle, the male couldn't discover his mistake.

  • Now, you might say, beetles, sure, they're very simple creatures,

  • but surely not mammals.

  • Mammals don't rely on tricks.

  • Well, I won't dwell on this, but you get the idea. (Laughter)

  • So this raises an important technical question:

  • Does natural selection really favor seeing reality as it is?

  • Fortunately, we don't have to wave our hands and guess;

  • evolution is a mathematically precise theory.

  • We can use the equations of evolution to check this out.

  • We can have various organisms in artificial worlds compete

  • and see which survive and which thrive,

  • which sensory systems are more fit.

  • A key notion in those equations is fitness.

  • Consider this steak:

  • What does this steak do for the fitness of an animal?

  • Well, for a hungry lion looking to eat, it enhances fitness.

  • For a well-fed lion looking to mate, it doesn't enhance fitness.

  • And for a rabbit in any state, it doesn't enhance fitness,

  • so fitness does depend on reality as it is, yes,

  • but also on the organism, its state and its action.

  • Fitness is not the same thing as reality as it is,

  • and it's fitness, and not reality as it is,

  • that figures centrally in the equations of evolution.

  • So, in my lab,

  • we have run hundreds of thousands of evolutionary game simulations

  • with lots of different randomly chosen worlds

  • and organisms that compete for resources in those worlds.

  • Some of the organisms see all of the reality,

  • others see just part of the reality,

  • and some see none of the reality,

  • only fitness.

  • Who wins?

  • Well, I hate to break it to you, but perception of reality goes extinct.

  • In almost every simulation,

  • organisms that see none of reality

  • but are just tuned to fitness

  • drive to extinction all the organisms that perceive reality as it is.

  • So the bottom line is, evolution does not favor vertical,

  • or accurate perceptions.

  • Those perceptions of reality go extinct.

  • Now, this is a bit stunning.

  • How can it be that not seeing the world accurately

  • gives us a survival advantage?

  • That is a bit counterintuitive.

  • But remember the jewel beetle.

  • The jewel beetle survived for thousands, perhaps millions of years,

  • using simple tricks and hacks.

  • What the equations of evolution are telling us

  • is that all organisms, including us, are in the same boat as the jewel beetle.

  • We do not see reality as it is.

  • We're shaped with tricks and hacks that keep us alive.

  • Still,

  • we need some help with our intuitions.

  • How can not perceiving reality as it is be useful?

  • Well, fortunately, we have a very helpful metaphor:

  • the desktop interface on your computer.

  • Consider that blue icon for a TED Talk that you're writing.

  • Now, the icon is blue and rectangular

  • and in the lower right corner of the desktop.

  • Does that mean that the text file itself in the computer is blue,

  • rectangular, and in the lower right-hand corner of the computer?

  • Of course not.

  • Anyone who thought that misinterprets the purpose of the interface.

  • It's not there to show you the reality of the computer.

  • In fact, it's there to hide that reality.

  • You don't want to know about the diodes

  • and resistors and all the megabytes of software.

  • If you had to deal with that, you could never write your text file

  • or edit your photo.

  • So the idea is that evolution has given us an interface

  • that hides reality and guides adaptive behavior.

  • Space and time, as you perceive them right now,

  • are your desktop.

  • Physical objects are simply icons in that desktop.

  • There's an obvious objection.

  • Hoffman, if you think that train coming down the track at 200 MPH

  • is just an icon of your desktop,

  • why don't you step in front of it?

  • And after you're gone, and your theory with you,

  • we'll know that there's more to that train than just an icon.

  • Well, I wouldn't step in front of that train

  • for the same reason

  • that I wouldn't carelessly drag that icon to the trash can:

  • not because I take the icon literally

  • the file is not literally blue or rectangular

  • but I do take it seriously.

  • I could lose weeks of work.

  • Similarly, evolution has shaped us

  • with perceptual symbols that are designed to keep us alive.

  • We'd better take them seriously.

  • If you see a snake, don't pick it up.

  • If you see a cliff, don't jump off.

  • They're designed to keep us safe, and we should take them seriously.

  • That does not mean that we should take them literally.

  • That's a logical error.

  • Another objection: There's nothing really new here.

  • Physicists have told us for a long time that the metal of that train looks solid

  • but really it's mostly empty space with microscopic particles zipping around.

  • There's nothing new here.

  • Well, not exactly.