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Just over a year ago,

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for the third time in my life,

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I ceased to exist.

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I was having a small operation,

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and my brain was filling with anesthetic.

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I remember a sense
of detachment and falling apart

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and a coldness.

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And then I was back,

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drowsy and disoriented,

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but definitely there.

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When you wake from a deep sleep,

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you might feel confused about the time
or anxious about oversleeping,

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but there's always a basic sense
of time having passed,

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of a continuity between then and now.

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Coming out from
anesthesia is very different.

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I could have been under for five minutes,

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five hours,

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five years,

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or even 50 years.

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I simply wasn't there.

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It was total obliviion.

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Anesthesia --

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it's a modern kind of magic.

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It turns people into objects,

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and then we hope,

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back again into people.

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In this process

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is one of the greatest remaining
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,

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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.

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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.

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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,

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we suffer consciously

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whether it's through
mental illness or pain.

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And if we can experience
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,

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maybe not too far away,

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when my iPhone develops
a sense of its own existence.

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I actually think the prospects
for a conscious AI are pretty remote.

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And I think this because
my research is telling me

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that consciousness has less to do
with pure intelligence

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and more to do with our nature
as living and breathing organisms.

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Consciousness and intelligence
are very different things.

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You don't have to be smart to suffer,

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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,

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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.

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Now, you might have heard
that we know nothing

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about how the brain and body
give rise to consciousness.

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Some people even say it's beyond
the reach of science all together.

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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.

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If you come to my lab 
at the University of Sussex,

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you'll find scientists
from all different disciplines,

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and sometimes even philosophers.

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All of us together trying to understand
how conscioussness happens

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and what happens when it goes wrong.

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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.

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At one time,

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people thought the property
of being alive could not be explained

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by physics and chemistry --

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that life had to be 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

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in terms of physics and chemistry --

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things like metabolism,
reproduction, homeostasis --

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the basic mystery of what life is
started to fade away,

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and people didn't propose
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,

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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,

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the apparently insoluble mystery
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?

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Well, for today I'd just like to think
of consciousness in two different ways.

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There are experiences
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.

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And then there's conscious self.

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The specific experience
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.

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Let's start with experiences
of the world around us,

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and with the important idea
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.

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There are no lights inside the skull.

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There's no sound either.

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All you've got to go on is streams
of electrical impulses

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which are only indirectly related
to things in the world,

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whatever they may be.

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So perception --

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figuring out what's there --

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has to be a process of informed guess work

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in which the brain combines
these sensory signals

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with its prior expectations or beliefs
about the way the world is

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to form its best guess 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.

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Let me give you a couple
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.

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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?

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But they are in fact
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,

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and join the two patches
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.

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It's a single colored block of gray,

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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,

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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

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built deeply into the circuits
of the visual cortex

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that a cast shadow dims
the appearance of a surface,

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so that we see B as lighter
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

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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.

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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: I think breakfast
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.

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I'm just going to replay it.

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([Distrorted voice])

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Yeah?

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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

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hasn't changed at all.

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All that's changed 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.

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All this puts the brain
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

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from the outside world,

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it depends as much,

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if not more,

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on perceptual predictions flowing
in the opposite direction.

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We don't just passively
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

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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

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as this active, constructive process.

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Here we've combined immersive
virtual reality with image processing

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to simulate the effects of overly
strong perceptual predictions

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on our experience.

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In this panoramic video,

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we've tranformed the world --

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which is in this case Sussex campus --

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into a psychedilic playground.

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We've processed the footage using
an alogrithm based on Google's Deep Dream

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to simulate the effects of overly strong
perceptual predictions.

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In this case, to see dogs.

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You can see this is a very strange thing.

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When perceptual
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 people might report

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in altered states,

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or perhaps even in psychosis.

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Think about this for a minute.

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If hallucination is a kind
of uncontrolled perception,

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then perception right here and right now
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

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by sensory information from the world.

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In fact, we're all
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,

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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,

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the specific experience of being you,

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is also a controlled hallucination
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,

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but how could I be deceived
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
is so familiar, so unified

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and so continuous

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that it's difficult 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.

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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

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from a first person point of view.

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There are experiences
of intending to do things

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and of being the cause of things
that happen in the world.

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And there are experiences of being
a continuous and distinctive person

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over time,

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built from a rich set of memories
and social interactions.

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Many experiments show,

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and psychiatrists and
neurologists know very well

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that these different ways 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

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of being a unified self is a rather
fragile construction of the brain,

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another experience,

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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

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and 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.

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There's a beautiful experiment
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 paint brushes.

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In the rubber hand illusion,

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a person's real hand is hidden from view.

262
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And that fake rubber hand
is placed in front of them.

263
00:10:25,044 --> 00:10:28,461
Then both hands are simultaneously
stroked with a paintbrush

264
00:10:28,657 --> 00:10:31,258
while the person stares at the fake hand.

265
00:10:31,645 --> 00:10:32,511
Now for most people,

266
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after a while,

267
00:10:33,721 --> 00:10:35,832
this leads to the very uncanny sensation

268
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that the fake hand is
in fact part of their body.

269
00:10:39,876 --> 00:10:44,192
And the idea is that the congruence
between seeing touch and feeling touch

270
00:10:44,375 --> 00:10:46,374
on an object that looks like hand,

271
00:10:46,581 --> 00:10:48,288
and is roughly where a hand should be,

272
00:10:48,493 --> 00:10:51,092
is enough evidence for the brain
to make its best guess

273
00:10:51,391 --> 00:10:55,046
that the fake hand is in fact
part of the body.

274
00:10:55,591 --> 00:10:56,666
(Laughter)

275
00:11:03,526 --> 00:11:05,610
So you can measure
all kinds of clever things.

276
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Like you can measure skin conductants

277
00:11:08,284 --> 00:11:09,210
and start and responses,

278
00:11:09,420 --> 00:11:10,039
but there's no need.

279
00:11:10,266 --> 00:11:13,277
It's clear the guy in blue
has assimilated the fake hand.

280
00:11:13,473 --> 00:11:16,710
This means that even experiences
of what our body is

281
00:11:16,893 --> 00:11:18,344
is kind of best guessing --

282
00:11:18,518 --> 00:11:20,951
a kind of controlled
hallucination by the brain.

283
99:59:59,999 --> 99:59:59,999
There's one more thing.

284
99:59:59,999 --> 99:59:59,999
We don't just experience our bodies
as objects in the world from the outside,

285
99:59:59,999 --> 99:59:59,999
we also experience them from within.

286
99:59:59,999 --> 99:59:59,999
We all experience the sense
of being a body from the inside.

287
99:59:59,999 --> 99:59:59,999
And sensory signals coming from
the inside of the body

288
99:59:59,999 --> 99:59:59,999
are continually telling the brain
about the state of the internal organs,

289
99:59:59,999 --> 99:59:59,999
how the heart is doing,

290
99:59:59,999 --> 99:59:59,999
what the blood pressure is like,

291
99:59:59,999 --> 99:59:59,999
lots of things.

292
99:59:59,999 --> 99:59:59,999
And this kind of perception,

293
99:59:59,999 --> 99:59:59,999
which we call intereception,

294
99:59:59,999 --> 99:59:59,999
is rather over-looked.

295
99:59:59,999 --> 99:59:59,999
But it's critically important

296
99:59:59,999 --> 99:59:59,999
because perception and regulation
of the internal state of the body --

297
99:59:59,999 --> 99:59:59,999
well, that's what keeps us alive.

298
99:59:59,999 --> 99:59:59,999
Here's another version of the
rubber hand illusion.

299
99:59:59,999 --> 99:59:59,999
This is from our lab at Sussex.

300
99:59:59,999 --> 99:59:59,999
And here, people see a virtual
reality version of their hand,

301
99:59:59,999 --> 99:59:59,999
which flashes red and back

302
99:59:59,999 --> 99:59:59,999
either in time or out of time
with their heartbeat.

303
99:59:59,999 --> 99:59:59,999
And when it's flashing in time
with their heartbeat,

304
99:59:59,999 --> 99:59:59,999
people have a strong sense that it's
in fact part of their body.

305
99:59:59,999 --> 99:59:59,999
So experiences of having a body
are deeply grounded

306
99:59:59,999 --> 99:59:59,999
in perceiving our bodies from within.

307
99:59:59,999 --> 99:59:59,999
There's one last thing I want
to draw your attention to,

308
99:59:59,999 --> 99:59:59,999
which is that experiences of the body
from the inside are very different

309
99:59:59,999 --> 99:59:59,999
from experiences of the world around us.

310
99:59:59,999 --> 99:59:59,999
When I look around me,

311
99:59:59,999 --> 99:59:59,999
the world seems full of objects --

312
99:59:59,999 --> 99:59:59,999
tables, chairs , rubber hands,

313
99:59:59,999 --> 99:59:59,999
people,

314
99:59:59,999 --> 99:59:59,999
[you lot] --

315
99:59:59,999 --> 99:59:59,999
even my own body in the world,

316
99:59:59,999 --> 99:59:59,999
I can perceive it as an object
from the outside,

317
99:59:59,999 --> 99:59:59,999
but my experiences of my body from within,

318
99:59:59,999 --> 99:59:59,999
they're not like that at all.

319
99:59:59,999 --> 99:59:59,999
I don't perceive my kidneys here,

320
99:59:59,999 --> 99:59:59,999
my liver here,

321
99:59:59,999 --> 99:59:59,999
my spleen ...

322
99:59:59,999 --> 99:59:59,999
I don't know where my spleen is,

323
99:59:59,999 --> 99:59:59,999
but somewhere.

324
99:59:59,999 --> 99:59:59,999
I don't perceive my insides as objects.

325
99:59:59,999 --> 99:59:59,999
In fact I don't experience them much
at all unless they go wrong.

326
99:59:59,999 --> 99:59:59,999
And this is important I think.

327
99:59:59,999 --> 99:59:59,999
Perception of the internal
state of the body

328
99:59:59,999 --> 99:59:59,999
isn't about figuring out what's there,

329
99:59:59,999 --> 99:59:59,999
it's about control and regulation --

330
99:59:59,999 --> 99:59:59,999
keeping the physiological variables
within the tight bounds

331
99:59:59,999 --> 99:59:59,999
that are compatible with survival.

332
99:59:59,999 --> 99:59:59,999
When the brain uses predictions
to figure out what's there,

333
99:59:59,999 --> 99:59:59,999
we can see objects
as the causes of sensations.

334
99:59:59,999 --> 99:59:59,999
When the brain uses predictions
to control and regulate things,

335
99:59:59,999 --> 99:59:59,999
we experience how well
or how badly that control is going.

336
99:59:59,999 --> 99:59:59,999
So out most basic experiences
of being a self,

337
99:59:59,999 --> 99:59:59,999
of being a body organism,

338
99:59:59,999 --> 99:59:59,999
are deeply grounded in the biological
mechanisms that keep us alive.

339
99:59:59,999 --> 99:59:59,999
And when we follow this idea
all the way through,

340
99:59:59,999 --> 99:59:59,999
we can start to see that all
of our conscious experiences,

341
99:59:59,999 --> 99:59:59,999
since they all depend on the same
mechanisms of predictive perception,

342
99:59:59,999 --> 99:59:59,999
all stem from this basic
drive to stay alive.

343
99:59:59,999 --> 99:59:59,999
We experience the world and ourselves

344
99:59:59,999 --> 99:59:59,999
with, through and because of
our living bodies.

345
99:59:59,999 --> 99:59:59,999
Let me bring things together step by step.

346
99:59:59,999 --> 99:59:59,999
What we consciously see depends
on the brain's best guess

347
99:59:59,999 --> 99:59:59,999
of what's out there.

348
99:59:59,999 --> 99:59:59,999
Our experienced world
comes from the inside out,

349
99:59:59,999 --> 99:59:59,999
not just the outside in.

350
99:59:59,999 --> 99:59:59,999
The rubber hand illusion shows
that this applies to our experienes

351
99:59:59,999 --> 99:59:59,999
of what is and what is not our body.

352
99:59:59,999 --> 99:59:59,999
And these self related predictions
depend critically on sensory signals

353
99:59:59,999 --> 99:59:59,999
coming from deep inside the body.

354
99:59:59,999 --> 99:59:59,999
And finally,

355
99:59:59,999 --> 99:59:59,999
experiences of being an embodied self
are more about control and regulation

356
99:59:59,999 --> 99:59:59,999
than figuring out what's there.

357
99:59:59,999 --> 99:59:59,999
So our experiences of the world
around us and ourselves within it --

358
99:59:59,999 --> 99:59:59,999
well, they're kinds
of controlled hallucinations

359
99:59:59,999 --> 99:59:59,999
that have been shaped
over millions of years of evolution

360
99:59:59,999 --> 99:59:59,999
to keep us alive in worlds
full of danger and opporunity.

361
99:59:59,999 --> 99:59:59,999
We predict ourselves into existence.

362
99:59:59,999 --> 99:59:59,999
Now I leave you with three
implications of all this.

363
99:59:59,999 --> 99:59:59,999
First, just as we can
misperceive the world,

364
99:59:59,999 --> 99:59:59,999
we can misperceive ourselves

365
99:59:59,999 --> 99:59:59,999
when the mechanisms
of prediction go wrong.

366
99:59:59,999 --> 99:59:59,999
Understanding this opens many new
opportunities in psychiatry and neurology,

367
99:59:59,999 --> 99:59:59,999
because we can finally
get at the mechanisms

368
99:59:59,999 --> 99:59:59,999
rather than just treating the symptoms

369
99:59:59,999 --> 99:59:59,999
in conditions like
depression and schizophrenia.

370
99:59:59,999 --> 99:59:59,999
Second:

371
99:59:59,999 --> 99:59:59,999
what it means to be me cannot be
reduced to or uploaded to

372
99:59:59,999 --> 99:59:59,999
a software program running on a robot,

373
99:59:59,999 --> 99:59:59,999
however smart or sophisticated.

374
99:59:59,999 --> 99:59:59,999
We are biological, flesh-and-blood animals

375
99:59:59,999 --> 99:59:59,999
whose conscious experiences
are shaped at all levels

376
99:59:59,999 --> 99:59:59,999
by the biological mechanisms
that keep us alive.

377
99:59:59,999 --> 99:59:59,999
Just making computers smarter
is not going to make the sentient.

378
99:59:59,999 --> 99:59:59,999
Finally,

379
99:59:59,999 --> 99:59:59,999
our own individual inner universe,

380
99:59:59,999 --> 99:59:59,999
our way of being conscious,

381
99:59:59,999 --> 99:59:59,999
is just one possible
way of being conscious.

382
99:59:59,999 --> 99:59:59,999
And even human consciousness generally --

383
99:59:59,999 --> 99:59:59,999
it's just a tiny region in a vast space
of possible consciousnesses.

384
99:59:59,999 --> 99:59:59,999
Our individual self and worlds
are unique to each of us,

385
99:59:59,999 --> 99:59:59,999
but they're all grounded

386
99:59:59,999 --> 99:59:59,999
in biological mechanisms shared
with many other living creatures.

387
99:59:59,999 --> 99:59:59,999
Now, these are fundamental changes
in how we understand ourselves,

388
99:59:59,999 --> 99:59:59,999
but I think they should be celebrated,

389
99:59:59,999 --> 99:59:59,999
because as so often in science,

390
99:59:59,999 --> 99:59:59,999
when Copernicus --

391
99:59:59,999 --> 99:59:59,999
we're not at the center
of the universe --

392
99:59:59,999 --> 99:59:59,999
to Darwin --

393
99:59:59,999 --> 99:59:59,999
we're related to all other creatures --

394
99:59:59,999 --> 99:59:59,999
to the present day.

395
99:59:59,999 --> 99:59:59,999
With a greater sense of understanding

396
99:59:59,999 --> 99:59:59,999
comes a greater sense of wonder,

397
99:59:59,999 --> 99:59:59,999
and a greater realization that we
are part of and not apart from

398
99:59:59,999 --> 99:59:59,999
the rest of nature.

399
99:59:59,999 --> 99:59:59,999
And when the end of consciousness comes,

400
99:59:59,999 --> 99:59:59,999
there's nothing to be afraid of.

401
99:59:59,999 --> 99:59:59,999
Nothing at all.

402
99:59:59,999 --> 99:59:59,999
Thank you.

403
99:59:59,999 --> 99:59:59,999
(Applause)