TED2017
Anil Seth: Your brain hallucinates your conscious reality
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Right now, billions of neurons in your brain are working together to generate a conscious experience -- and not just any conscious experience, your experience of the world around you and of yourself within it. How does this happen? According to neuroscientist Anil Seth, we're all hallucinating all the time; when we agree about our hallucinations, we call it "reality." Join Seth for a delightfully disorienting talk that may leave you questioning the very nature of your existence.
Anil Seth - Cognitive neuroscientist
How can the "inner universe" of consciousness be explained in terms of mere biology and physics? Anil Seth explores the brain basis of consciousness and self. Full bio
How can the "inner universe" of consciousness be explained in terms of mere biology and physics? Anil Seth explores the brain basis of consciousness and self. Full bio
Double-click the English transcript below to play the video.
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Just over a year ago,
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for the third time in my life,
I ceased to exist.
I ceased to exist.
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I was having a small operation,
and my brain was filling with anesthetic.
and my brain was filling with anesthetic.
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I remember a sense
of detachment and falling apart
of detachment and falling apart
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and a coldness.
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And then I was back,
drowsy and disoriented,
drowsy and disoriented,
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but definitely there.
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Now, when you wake from a deep sleep,
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you might feel confused about the time
or anxious about oversleeping,
or anxious about oversleeping,
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but there's always a basic sense
of time having passed,
of time having passed,
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of a continuity between then and now.
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Coming round from
anesthesia is very different.
anesthesia is very different.
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I could have been under
for five minutes, five hours,
for five minutes, five hours,
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five years or even 50 years.
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I simply wasn't there.
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It was total oblivion.
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Anesthesia --
it's a modern kind of magic.
it's a modern kind of magic.
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It turns people into objects,
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and then, we hope, back again into people.
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And in this process
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is one of the greatest remaining
mysteries in science and philosophy.
mysteries in science and philosophy.
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How does consciousness happen?
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Somehow, within each of our brains,
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the combined activity
of many billions of neurons,
of many billions of neurons,
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each one a tiny biological machine,
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is generating a conscious experience.
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And not just any conscious experience --
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your conscious experience
right here and right now.
right here and right now.
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How does this happen?
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Answering this question is so important
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because consciousness
for each of us is all there is.
for each of us is all there is.
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Without it there's no world,
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there's no self,
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there's nothing at all.
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And when we suffer, we suffer consciously
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whether it's through
mental illness or pain.
mental illness or pain.
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And if we can experience
joy and suffering,
joy and suffering,
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what about other animals?
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Might they be conscious, too?
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Do they also have a sense of self?
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And as computers get faster and smarter,
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maybe there will come a point,
maybe not too far away,
maybe not too far away,
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when my iPhone develops
a sense of its own existence.
a sense of its own existence.
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I actually think the prospects
for a conscious AI are pretty remote.
for a conscious AI are pretty remote.
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And I think this because
my research is telling me
my research is telling me
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that consciousness has less to do
with pure intelligence
with pure intelligence
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and more to do with our nature
as living and breathing organisms.
as living and breathing organisms.
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Consciousness and intelligence
are very different things.
are very different things.
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You don't have to be smart to suffer,
but you probably do have to be alive.
but you probably do have to be alive.
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In the story I'm going to tell you,
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our conscious experiences
of the world around us,
of the world around us,
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and of ourselves within it,
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are kinds of controlled hallucinations
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that happen with, through
and because of our living bodies.
and because of our living bodies.
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Now, you might have heard
that we know nothing
that we know nothing
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about how the brain and body
give rise to consciousness.
give rise to consciousness.
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Some people even say it's beyond
the reach of science altogether.
the reach of science altogether.
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But in fact,
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the last 25 years have seen an explosion
of scientific work in this area.
of scientific work in this area.
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If you come to my lab
at the University of Sussex,
at the University of Sussex,
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you'll find scientists
from all different disciplines
from all different disciplines
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and sometimes even philosophers.
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All of us together trying to understand
how consciousness happens
how consciousness happens
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and what happens when it goes wrong.
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And the strategy is very simple.
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I'd like you to think about consciousness
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in the way that we've
come to think about life.
come to think about life.
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At one time, people thought
the property of being alive
the property of being alive
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could not be explained
by physics and chemistry --
by physics and chemistry --
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that life had to be
more than just mechanism.
more than just mechanism.
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But people no longer think that.
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As biologists got on with the job
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of explaining the properties
of living systems
of living systems
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in terms of physics and chemistry --
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things like metabolism,
reproduction, homeostasis --
reproduction, homeostasis --
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the basic mystery of what life is
started to fade away,
started to fade away,
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and people didn't propose
any more magical solutions,
any more magical solutions,
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like a force of life or an élan vital.
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So as with life, so with consciousness.
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Once we start explaining its properties
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in terms of things happening
inside brains and bodies,
inside brains and bodies,
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the apparently insoluble mystery
of what consciousness is
of what consciousness is
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should start to fade away.
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At least that's the plan.
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So let's get started.
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What are the properties of consciousness?
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What should a science
of consciousness try to explain?
of consciousness try to explain?
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Well, for today I'd just like to think
of consciousness in two different ways.
of consciousness in two different ways.
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There are experiences
of the world around us,
of the world around us,
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full of sights, sounds and smells,
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there's multisensory, panoramic,
3D, fully immersive inner movie.
3D, fully immersive inner movie.
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And then there's conscious self.
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The specific experience
of being you or being me.
of being you or being me.
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The lead character in this inner movie,
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and probably the aspect of consciousness
we all cling to most tightly.
we all cling to most tightly.
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Let's start with experiences
of the world around us,
of the world around us,
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and with the important idea
of the brain as a prediction engine.
of the brain as a prediction engine.
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Imagine being a brain.
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You're locked inside a bony skull,
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trying to figure
what's out there in the world.
what's out there in the world.
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There's no lights inside the skull.
There's no sound either.
There's no sound either.
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All you've got to go on
is streams of electrical impulses
is streams of electrical impulses
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which are only indirectly related
to things in the world,
to things in the world,
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whatever they may be.
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So perception --
figuring out what's there --
figuring out what's there --
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has to be a process of informed guesswork
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in which the brain combines
these sensory signals
these sensory signals
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with its prior expectations or beliefs
about the way the world is
about the way the world is
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to form its best guess
of what caused those signals.
of what caused those signals.
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The brain doesn't hear sound or see light.
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What we perceive is its best guess
of what's out there in the world.
of what's out there in the world.
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Let me give you a couple
of examples of all this.
of examples of all this.
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You might have seen this illusion before,
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but I'd like you to think
about it in a new way.
about it in a new way.
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If you look at those two patches, A and B,
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they should look to you to be
very different shades of gray, right?
very different shades of gray, right?
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But they are in fact
exactly the same shade.
exactly the same shade.
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And I can illustrate this.
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If I put up a second version
of the image here
of the image here
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and join the two patches
with a gray-colored bar,
with a gray-colored bar,
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you can see there's no difference.
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It's exactly the same shade of gray.
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And if you still don't believe me,
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I'll bring the bar across
and join them up.
and join them up.
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It's a single colored block of gray,
there's no difference at all.
there's no difference at all.
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This isn't any kind of magic trick.
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It's the same shade of gray,
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but take it away again,
and it looks different.
and it looks different.
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So what's happening here
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is that the brain
is using its prior expectations
is using its prior expectations
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built deeply into the circuits
of the visual cortex
of the visual cortex
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that a cast shadow dims
the appearance of a surface,
the appearance of a surface,
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so that we see B as lighter
than it really is.
than it really is.
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Here's one more example,
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which shows just how quickly
the brain can use new predictions
the brain can use new predictions
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to change what we consciously experience.
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Have a listen to this.
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(Distorted voice)
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Sounded strange, right?
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Have a listen again
and see if you can get anything.
and see if you can get anything.
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(Distorted voice)
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Still strange.
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Now listen to this.
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(Recording) Anil Seth: I think Brexit
is a really terrible idea.
is a really terrible idea.
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(Laughter)
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Which I do.
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So you heard some words there, right?
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Now listen to the first sound again.
I'm just going to replay it.
I'm just going to replay it.
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(Distorted voice)
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Yeah? So you can now hear words there.
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Once more for luck.
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(Distorted voice)
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OK, so what's going on here?
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The remarkable thing is the sensory
information coming into the brain
information coming into the brain
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hasn't changed at all.
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All that's changed
is your brain's best guess
is your brain's best guess
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of the causes of that sensory information.
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And that changes
what you consciously hear.
what you consciously hear.
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All this puts the brain
basis of perception
basis of perception
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in a bit of a different light.
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Instead of perception depending largely
on signals coming into the brain
on signals coming into the brain
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from the outside world,
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it depends as much, if not more,
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on perceptual predictions
flowing in the opposite direction.
flowing in the opposite direction.
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We don't just passively
perceive the world,
perceive the world,
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we actively generate it.
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The world we experience
comes as much, if not more,
comes as much, if not more,
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from the inside out
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as from the outside in.
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Let me give you
one more example of perception
one more example of perception
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as this active, constructive process.
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Here we've combined immersive
virtual reality with image processing
virtual reality with image processing
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to simulate the effects
of overly strong perceptual predictions
of overly strong perceptual predictions
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on experience.
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In this panoramic video,
we've transformed the world --
we've transformed the world --
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which is in this case Sussex campus --
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into a psychedelic playground.
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We've processed the footage using
an algorithm based on Google's Deep Dream
an algorithm based on Google's Deep Dream
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to simulate the effects
of overly strong perceptual predictions.
of overly strong perceptual predictions.
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In this case, to see dogs.
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And you can see
this is a very strange thing.
this is a very strange thing.
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When perceptual
predictions are too strong,
predictions are too strong,
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as they are here,
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the result looks very much
like the kinds of hallucinations
like the kinds of hallucinations
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people might report in altered states,
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or perhaps even in psychosis.
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Now, think about this for a minute.
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If hallucination is a kind
of uncontrolled perception,
of uncontrolled perception,
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then perception right here and right now
is also a kind of hallucination,
is also a kind of hallucination,
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but a controlled hallucination
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in which the brain's predictions
are being reigned in
are being reigned in
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by sensory information from the world.
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In fact, we're all
hallucinating all the time,
hallucinating all the time,
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including right now.
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It's just that when we agree
about our hallucinations,
about our hallucinations,
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we call that reality.
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(Laughter)
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Now I'm going to tell you
that your experience of being a self,
that your experience of being a self,
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the specific experience of being you,
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is also a controlled hallucination
generated by the brain.
generated by the brain.
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This seems a very strange idea, right?
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Yes, visual illusions
might deceive my eyes,
might deceive my eyes,
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but how could I be deceived
about what it means to be me?
about what it means to be me?
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For most of us,
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the experience of being a person
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is so familiar, so unified
and so continuous
and so continuous
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that it's difficult
not to take it for granted.
not to take it for granted.
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But we shouldn't take it for granted.
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There are in fact many different ways
we experience being a self.
we experience being a self.
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There's the experience of having a body
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and of being a body.
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There are experiences
of perceiving the world
of perceiving the world
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from a first person point of view.
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There are experiences
of intending to do things
of intending to do things
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and of being the cause of things
that happen in the world.
that happen in the world.
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And there are experiences
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of being a continuous
and distinctive person over time,
and distinctive person over time,
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built from a rich set
of memories and social interactions.
of memories and social interactions.
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Many experiments show,
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and psychiatrists
and neurologists know very well,
and neurologists know very well,
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that these different ways
in which we experience being a self
in which we experience being a self
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can all come apart.
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What this means is
the basic background experience
the basic background experience
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of being a unified self is a rather
fragile construction of the brain.
fragile construction of the brain.
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Another experience,
which just like all others,
which just like all others,
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requires explanation.
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So let's return to the bodily self.
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How does the brain generate
the experience of being a body
the experience of being a body
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and of having a body?
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Well, just the same principles apply.
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The brain makes its best guess
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about what is and what is not
part of its body.
part of its body.
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And there's a beautiful experiment
in neuroscience to illustrate this.
in neuroscience to illustrate this.
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And unlike most neuroscience experiments,
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this is one you can do at home.
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All you need is one of these.
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(Laughter)
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And a couple of paintbrushes.
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In the rubber hand illusion,
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a person's real hand is hidden from view,
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and that fake rubber hand
is placed in front of them.
is placed in front of them.
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Then both hands are simultaneously
stroked with a paintbrush
stroked with a paintbrush
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while the person stares at the fake hand.
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Now, for most people, after a while,
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this leads to the very uncanny sensation
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that the fake hand
is in fact part of their body.
is in fact part of their body.
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And the idea is that the congruence
between seeing touch and feeling touch
between seeing touch and feeling touch
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on an object that looks like hand
and is roughly where a hand should be,
and is roughly where a hand should be,
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is enough evidence for the brain
to make its best guess
to make its best guess
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that the fake hand
is in fact part of the body.
is in fact part of the body.
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(Laughter)
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So you can measure
all kinds of clever things.
all kinds of clever things.
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You can measure skin conductance
and startle responses,
and startle responses,
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but there's no need.
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It's clear the guy in blue
has assimilated the fake hand.
has assimilated the fake hand.
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This means that even experiences
of what our body is
of what our body is
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is a kind of best guessing --
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a kind of controlled
hallucination by the brain.
hallucination by the brain.
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There's one more thing.
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We don't just experience our bodies
as objects in the world from the outside,
as objects in the world from the outside,
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we also experience them from within.
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We all experience the sense
of being a body from the inside.
of being a body from the inside.
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And sensory signals
coming from the inside of the body
coming from the inside of the body
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are continually telling the brain
about the state of the internal organs,
about the state of the internal organs,
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how the heart is doing,
what the blood pressure is like,
what the blood pressure is like,
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lots of things.
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This kind of perception,
which we call interoception,
which we call interoception,
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is rather overlooked.
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But it's critically important
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because perception and regulation
of the internal state of the body --
of the internal state of the body --
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well, that's what keeps us alive.
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Here's another version
of the rubber hand illusion.
of the rubber hand illusion.
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This is from our lab at Sussex.
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And here, people see
a virtual reality version of their hand,
a virtual reality version of their hand,
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which flashes red and back
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either in time or out of time
with their heartbeat.
with their heartbeat.
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And when it's flashing
in time with their heartbeat,
in time with their heartbeat,
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people have a stronger sense
that it's in fact part of their body.
that it's in fact part of their body.
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So experiences of having a body
are deeply grounded
are deeply grounded
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in perceiving our bodies from within.
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There's one last thing
I want to draw your attention to,
I want to draw your attention to,
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which is that experiences of the body
from the inside are very different
from the inside are very different
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from experiences of the world around us.
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When I look around me,
the world seems full of objects --
the world seems full of objects --
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tables, chairs, rubber hands,
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people, you lot --
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even my own body in the world,
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I can perceive it
as an object from the outside.
as an object from the outside.
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But my experiences
of the body from within,
of the body from within,
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they're not like that at all.
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I don't perceive my kidneys here,
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my liver here,
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my spleen ...
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I don't know where my spleen is,
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but it's somewhere.
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I don't perceive my insides as objects.
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In fact, I don't experience them
much at all unless they go wrong.
much at all unless they go wrong.
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And this is important, I think.
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Perception of the internal
state of the body
state of the body
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isn't about figuring out what's there,
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it's about control and regulation --
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keeping the physiological variables
within the tight bounds
within the tight bounds
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that are compatible with survival.
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13:28
When the brain uses predictions
to figure out what's there,
to figure out what's there,
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we perceive objects
as the causes of sensations.
as the causes of sensations.
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When the brain uses predictions
to control and regulate things,
to control and regulate things,
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we experience how well
or how badly that control is going.
or how badly that control is going.
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So our most basic experiences
of being a self,
of being a self,
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of being an embodied organism,
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are deeply grounded in the biological
mechanisms that keep us alive.
mechanisms that keep us alive.
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And when we follow this idea
all the way through,
all the way through,
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we can start to see
that all of our conscious experiences,
that all of our conscious experiences,
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since they all depend on the same
mechanisms of predictive perception,
mechanisms of predictive perception,
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all stem from this basic
drive to stay alive.
drive to stay alive.
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We experience the world and ourselves
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with, through and because of
our living bodies.
our living bodies.
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Let me bring things together step-by-step.
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What we consciously see depends
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on the brain's best guess
of what's out there.
of what's out there.
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Our experienced world
comes from the inside out,
comes from the inside out,
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not just the outside in.
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The rubber hand illusion shows
that this applies to our experiences
that this applies to our experiences
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14:27
of what is and what is not our body.
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And these self-related predictions
depend critically on sensory signals
depend critically on sensory signals
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coming from deep inside the body.
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And finally,
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experiences of being an embodied self
are more about control and regulation
are more about control and regulation
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14:42
than figuring out what's there.
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14:44
So our experiences of the world
around us and ourselves within it --
around us and ourselves within it --
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well, they're kinds
of controlled hallucinations
of controlled hallucinations
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that have been shaped
over millions of years of evolution
over millions of years of evolution
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to keep us alive in worlds
full of danger and opportunity.
full of danger and opportunity.
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We predict ourselves into existence.
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Now, I leave you with three
implications of all this.
implications of all this.
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First, just as we can
misperceive the world,
misperceive the world,
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we can misperceive ourselves
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when the mechanisms
of prediction go wrong.
of prediction go wrong.
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Understanding this opens many new
opportunities in psychiatry and neurology,
opportunities in psychiatry and neurology,
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because we can finally
get at the mechanisms
get at the mechanisms
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rather than just treating the symptoms
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in conditions like
depression and schizophrenia.
depression and schizophrenia.
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Second:
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what it means to be me
cannot be reduced to or uploaded to
cannot be reduced to or uploaded to
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a software program running on a robot,
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however smart or sophisticated.
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We are biological, flesh-and-blood animals
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whose conscious experiences
are shaped at all levels
are shaped at all levels
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by the biological mechanisms
that keep us alive.
that keep us alive.
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Just making computers smarter
is not going to make them sentient.
is not going to make them sentient.
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Finally,
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our own individual inner universe,
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15:48
our way of being conscious,
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is just one possible
way of being conscious.
way of being conscious.
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And even human consciousness generally --
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it's just a tiny region in a vast space
of possible consciousnesses.
of possible consciousnesses.
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Our individual self and worlds
are unique to each of us,
are unique to each of us,
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but they're all grounded
in biological mechanisms
in biological mechanisms
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shared with many other living creatures.
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Now, these are fundamental changes
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in how we understand ourselves,
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but I think they should be celebrated,
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because as so often in science,
from Copernicus --
from Copernicus --
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we're not at the center of the universe --
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to Darwin --
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we're related to all other creatures --
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to the present day.
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With a greater sense of understanding
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comes a greater sense of wonder,
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and a greater realization
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that we are part of
and not apart from the rest of nature.
and not apart from the rest of nature.
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And ...
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when the end of consciousness comes,
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there's nothing to be afraid of.
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Nothing at all.
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Thank you.
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(Applause)
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ABOUT THE SPEAKER
Anil Seth - Cognitive neuroscientistHow can the "inner universe" of consciousness be explained in terms of mere biology and physics? Anil Seth explores the brain basis of consciousness and self.
Why you should listen
In his groundbreaking research, Anil Seth seeks to understand consciousness in health and in disease. As founding co-director of the University of Sussex’s Sackler Centre for Consciousness Science, his research bridges neuroscience, mathematics, artificial intelligence, computer science, psychology, philosophy and psychiatry. He has also worked extensively with playwrights, dancers and other artists to shape a truly humanistic view of consciousness and self.
Seth is the editor and co-author of the best-selling 30-Second Brain, a collection of brief and engaging neuroscience vignettes. His forthcoming book The Presence Chamber develops his unique theories of conscious selfhood within the rich historical context of the mind and brain sciences.
Follow Seth on Twitter at @anilkseth, and visit his website at anilseth.com and neurobanter.com. The Sackler Centre, at the University of Sussex, is at sussex.ac.uk/sackler. Seth's work is supported by the Dr. Mortimer and Theresa Sackler Foundation.
Anil Seth | Speaker | TED.com