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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 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.

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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
00:10:22,486 --> 00:10:25,068
and that fake rubber hand
is placed in front of them.

263
00:10:25,068 --> 00:10:28,581
Then both hands are simultaneously
stroked with a paintbrush

264
00:10:28,581 --> 00:10:31,352
while the person stares at the fake hand.

265
00:10:31,545 --> 00:10:32,611
Now for most people,

266
00:10:32,611 --> 00:10:33,622
after a while,

267
00:10:33,622 --> 00:10:35,863
this leads to the very uncanny sensation

268
00:10:35,863 --> 00:10:38,828
that the fake hand is
in fact part of their body.

269
00:10:39,786 --> 00:10:44,222
And the idea is that the congruence
between seeing touch and feeling touch

270
00:10:44,222 --> 00:10:46,431
on an object that looks like hand,

271
00:10:46,431 --> 00:10:48,488
and is roughly where a hand should be,

272
00:10:48,488 --> 00:10:51,357
is enough evidence for the brain
to make its best guess

273
00:10:51,357 --> 00:10:54,922
that the fake hand is in fact
part of the body.

274
00:10:54,922 --> 00:10:56,877
(Laughter)

275
00:11:03,426 --> 00:11:05,700
So you can measure
all kinds of clever things.

276
00:11:05,700 --> 00:11:08,042
Like you can measure skin conductants

277
00:11:08,042 --> 00:11:09,218
and [startle] responses,

278
00:11:09,218 --> 00:11:10,217
but there's no need.

279
00:11:10,217 --> 00:11:13,227
It's clear the guy in blue
has assimilated the fake hand.

280
00:11:13,383 --> 00:11:16,800
This means that even experiences
of what our body is

281
00:11:16,800 --> 00:11:18,381
is kind of best guessing --

282
00:11:18,381 --> 00:11:21,094
a kind of controlled
hallucination by the brain.

283
00:11:21,809 --> 00:11:23,590
There's one more thing.

284
00:11:24,334 --> 00:11:28,006
We don't just experience our bodies
as objects in the world from the outside,

285
00:11:28,006 --> 00:11:29,950
we also experience them from within.

286
00:11:29,950 --> 00:11:34,643
We all experience the sense
of being a body from the inside.

287
00:11:35,175 --> 00:11:37,831
And sensory signals coming from
the inside of the body

288
00:11:37,831 --> 00:11:41,937
are continually telling the brain
about the state of the internal organs,

289
00:11:41,937 --> 00:11:43,186
how the heart is doing,

290
00:11:43,186 --> 00:11:44,726
what the blood pressure is like,

291
00:11:44,726 --> 00:11:45,728
lots of things.

292
00:11:45,728 --> 00:11:46,916
This kind of perception,

293
00:11:46,916 --> 00:11:49,170
which we call interoception,

294
00:11:49,170 --> 00:11:50,239
is rather overlooked.

295
00:11:50,239 --> 00:11:51,645
But it's critically important

296
00:11:51,645 --> 00:11:55,212
because perception and regulation
of the internal state of the body --

297
00:11:55,212 --> 00:11:56,911
well, that's what keeps us alive.

298
00:11:57,573 --> 00:11:59,980
Here's another version
of the rubber hand illusion.

299
00:11:59,980 --> 00:12:01,643
This is from our lab at Sussex.

300
00:12:01,643 --> 00:12:05,087
And here, people see a virtual
reality version of their hand,

301
00:12:05,087 --> 00:12:06,504
which flashes [red and back]

302
00:12:06,504 --> 00:12:09,608
either in time or out of time
with their heartbeat.

303
00:12:09,608 --> 00:12:12,044
And when it's flashing in time
with their heartbeat,

304
00:12:12,044 --> 00:12:15,745
people have a stronger sense
that it's in fact part of their body.

305
00:12:16,010 --> 00:12:19,485
So experiences of having a body
are deeply grounded

306
00:12:19,485 --> 00:12:22,664
in perceiving our bodies from within.

307
00:12:23,742 --> 00:12:26,471
There's one last thing I want
to draw your attention to,

308
00:12:26,471 --> 00:12:30,477
which is that experiences of the body
from the inside are very different

309
00:12:30,477 --> 00:12:32,404
from experiences of the world around us.

310
00:12:32,404 --> 00:12:33,484
When I look around me,

311
00:12:33,484 --> 00:12:35,121
the world seems full of objects --

312
00:12:35,121 --> 00:12:37,372
tables, chairs, rubber hands,

313
00:12:37,372 --> 00:12:38,365
people,

314
00:12:38,365 --> 00:12:39,366
[you lot] --

315
00:12:39,366 --> 00:12:41,195
even my own body in the world,

316
00:12:41,195 --> 00:12:43,439
I can perceive it as an object
from the outside,

317
00:12:43,439 --> 00:12:45,459
but my experiences
of the body from within,

318
00:12:45,459 --> 00:12:46,851
they're not like that at all.

319
00:12:46,851 --> 00:12:48,972
I don't perceive my kidneys here,

320
00:12:48,972 --> 00:12:50,516
my liver here,

321
00:12:50,516 --> 00:12:51,830
my spleen ...

322
00:12:51,830 --> 00:12:53,641
I don't know where my spleen is,

323
00:12:53,641 --> 00:12:55,187
but it's somewhere.

324
00:12:55,187 --> 00:12:57,243
I don't perceive my insides as objects.

325
00:12:57,243 --> 00:13:01,219
In fact, I don't experience them
much at all unless they go wrong.

326
00:13:01,715 --> 00:13:03,750
And this is important I think.

327
00:13:03,750 --> 00:13:05,814
Perception of the internal
state of the body

328
00:13:05,814 --> 00:13:07,918
isn't about figuring out what's there,

329
00:13:07,918 --> 00:13:10,009
it's about control and regulation --

330
00:13:10,009 --> 00:13:13,910
keeping the physiological variables
within the tight bounds

331
00:13:13,910 --> 00:13:16,141
that are compatible with survival.

332
00:13:16,889 --> 00:13:19,920
When the brain uses predictions
to figure out what's there,

333
00:13:19,920 --> 00:13:22,931
we can see objects
as the causes of sensations.

334
00:13:22,931 --> 00:13:26,485
When the brain uses predictions
to control and regulate things,

335
00:13:26,485 --> 00:13:29,627
we experience how well
or how badly that control is going.

336
00:13:29,978 --> 00:13:33,040
So our most basic experiences
of being a self,

337
00:13:33,040 --> 00:13:35,185
of being an embodied organism,

338
00:13:35,185 --> 00:13:39,222
are deeply grounded in the biological
mechanisms that keep us alive.

339
00:13:40,941 --> 00:13:43,470
When we follow this idea
all the way through,

340
00:13:43,470 --> 00:13:47,111
we can start to see that all
of our conscious experiences,

341
00:13:47,111 --> 00:13:51,806
since they all depend on the same
mechanisms of predictive perception,

342
00:13:51,806 --> 00:13:55,297
all stem from this basic
drive to stay alive.

343
00:13:55,297 --> 00:13:58,020
We experience the world and ourselves

344
00:13:58,020 --> 00:14:01,481
with, through and because of
our living bodies.

345
00:14:01,787 --> 00:14:04,442
Let me bring things together step-by-step.

346
00:14:04,779 --> 00:14:07,461
What we consciously see depends
on the brain's best guess

347
00:14:07,461 --> 00:14:08,848
of what's out there.

348
00:14:08,848 --> 00:14:11,208
Our experienced world
comes from the inside out,

349
00:14:11,208 --> 00:14:12,814
not just the outside in.

350
00:14:12,814 --> 00:14:16,150
The rubber hand illusion shows
that this applies to our experienes

351
00:14:16,150 --> 00:14:18,448
of what is and what is not our body.

352
00:14:18,783 --> 00:14:22,449
And these self-related predictions
depend critically on sensory signals

353
00:14:22,449 --> 00:14:24,409
coming from deep inside the body.

354
00:14:24,619 --> 00:14:25,619
And finally,

355
00:14:25,619 --> 00:14:30,336
experiences of being an embodied self
are more about control and regulation

356
00:14:30,336 --> 00:14:32,604
than figuring out what's there.

357
00:14:32,988 --> 00:14:36,194
So our experiences of the world
around us and ourselves within it --

358
00:14:36,194 --> 00:14:38,452
well, they're kinds
of controlled hallucinations

359
00:14:38,452 --> 00:14:41,591
that have been shaped
over millions of years of evolution

360
00:14:41,591 --> 00:14:44,662
to keep us alive in worlds
full of danger and opportunity.

361
00:14:44,958 --> 00:14:47,746
We predict ourselves into existence.

362
00:14:48,634 --> 00:14:51,263
Now I leave you with three
implications of all this.

363
00:14:51,705 --> 00:14:54,055
First, just as we can
misperceive the world,

364
00:14:54,055 --> 00:14:55,812
we can misperceive ourselves

365
00:14:55,812 --> 00:14:58,241
when the mechanisms
of prediction go wrong.

366
00:14:58,241 --> 00:15:02,334
Understanding this opens many new
opportunities in psychiatry and neurology,

367
00:15:02,334 --> 00:15:05,039
because we can finally
get at the mechanisms

368
00:15:05,039 --> 00:15:06,898
rather than just treating the symptoms

369
00:15:06,898 --> 00:15:09,688
in conditions like
depression and schizophrenia.

370
00:15:09,942 --> 00:15:11,093
Second:

371
00:15:11,093 --> 00:15:15,093
what it means to be me cannot be
reduced to or uploaded to

372
00:15:15,093 --> 00:15:17,475
a software program running on a robot,

373
00:15:17,475 --> 00:15:19,538
however smart or sophisticated.

374
00:15:19,538 --> 00:15:22,267
We are biological, flesh-and-blood animals

375
00:15:22,267 --> 00:15:25,560
whose conscious experiences
are shaped at all levels

376
00:15:25,560 --> 00:15:28,528
by the biological mechanisms
that keep us alive.

377
00:15:28,528 --> 00:15:32,585
Just making computers smarter
is not going to make the sentient.

378
00:15:33,191 --> 00:15:34,710
Finally,

379
00:15:34,710 --> 00:15:36,584
our own individual inner universe,

380
00:15:36,584 --> 00:15:38,106
our way of being conscious,

381
00:15:38,106 --> 00:15:41,444
is just one possible
way of being conscious.

382
00:15:41,955 --> 00:15:43,938
And even human consciousness generally --

383
00:15:43,938 --> 00:15:48,150
it's just a tiny region in a vast space
of possible consciousnesses.

384
00:15:48,150 --> 00:15:51,830
Our individual self and worlds
are unique to each of us,

385
00:15:51,830 --> 00:15:53,816
but they're all grounded

386
00:15:53,816 --> 00:15:57,707
in biological mechanisms shared
with many other living creatures.

387
00:15:58,089 --> 00:16:04,190
Now, these are fundamental changes
in how we understand ourselves,

388
00:16:04,190 --> 00:16:06,018
but I think they should be celebrated,

389
00:16:06,018 --> 00:16:07,497
because as so often in science,

390
00:16:07,497 --> 00:16:08,497
when Copernicus --

391
00:16:08,497 --> 00:16:10,476
we're not at the center
of the universe --

392
00:16:10,476 --> 00:16:11,622
to Darwin --

393
00:16:11,622 --> 00:16:14,101
we're related to all other creatures --

394
00:16:14,101 --> 00:16:15,918
to the present day.

395
00:16:16,620 --> 00:16:19,255
With a greater sense of understanding

396
00:16:19,255 --> 00:16:21,817
comes a greater sense of wonder,

397
00:16:21,817 --> 00:16:27,168
and a greater realization that we
are part of and not apart from

398
00:16:27,168 --> 00:16:28,738
the rest of nature.

399
00:16:29,038 --> 00:16:30,946
And ...

400
00:16:30,946 --> 00:16:33,461
when the end of consciousness comes,

401
00:16:33,461 --> 00:16:36,814
there's nothing to be afraid of.

402
00:16:36,814 --> 00:16:38,444
Nothing at all.

403
00:16:38,765 --> 00:16:39,962
Thank you.

404
00:16:39,962 --> 00:16:42,226
(Applause)