WEBVTT

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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 seized 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 minute,

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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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And 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 or 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 conciously,

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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 chemisty.

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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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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 out what's
out there in the world.

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There's 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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and 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 joing 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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So 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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([Sound])

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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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([Sound])

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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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([Recording])

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Yeah?

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(Laughter)

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So you can now hear words there.

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One more more for luck.

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([Recording])

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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