What is reality?
Infinite Monkey Cage
Transcription of BBC Podcast - 2 Feb 2016
Hosts
Robin Ince (RI):
Comedian, actor and writer.
Professor Brian Cox
(PBC): Physicist and Advanced Fellow of particle physics in the School of
Physics and Astronomy at the University of Manchester.
Panellists:
David Eagleman (DE): Neuroscientist.
Directs the Laboratory for Perception and Action at the Baylor College of
Medicine, and also heads the Centre for Science and Law. He is best known for
his work on sensory substitution, time perception, brain plasticity, synaesthesia,
and neurolaw.
Professor Sophie
Scott (SS): Deputy Director at the UCL Institute of Cognitive Neuroscience,
researching the neuroscience of voices, speech and laughter.
Bridget Christie (BC): Comedian, actress and writer
PBC
How do our brains put
together our picture of the world? There clearly is a physical reality outside
our brains, so when we ask the question what is reality, what are we actually
asking?
DE
I’m asking - what do we perceive? We all have this private,
subjective experience from the moment you wake up in the morning and you feel
like you are being flooded with your senses, but that is a construction of your
brain. It sometimes has very little to do with what’s in the outside world so
of course there’s an objective reality out there, and the job of physics is to
figure out what that looks like. But what you perceive, how you misperceive
things, how you perceive colours and the taste of feta cheese and your whole
world on the inside – that’s the part I’m interested in – that reality.
PBC
So the job of physics
is to describe things as they really are and the job of biology is to sort out
the mistakes?
[Laughter]
DE
Er… No! I see biology - neuroscience in particular - as a
really strong inroad into understanding ourselves and why we have the kind of
experiences we do, but we have to work through this filter of our psychology,
the way we even build physics and there’s a lot of physics that we won’t have
discovered yet or will be difficult to discover because of the way we are
trapped inside of our own heads
RI
So how much can we
know of what kind of shared reality we actually have?
SS
Part of it comes from just doing straightforward, good
psychology and investigating how people perceive stuff, and finding what is
common across people and if you think about it if we didn’t have some shared
reality then we wouldn’t be able to use language because words wouldn’t have
the same meaning. If my meaning of red meant totally different to everyone
else’s there’d be no point in having it for any kind of meaningful discussion
with people.
Basically the history of a lot of psychology has been
spelling out the tremendous mismatches between what the world feels like and
what we are actually perceiving. And visual processing is a very good example.
I feel if I am looking at everyone on the panel - I can see where David as and
where Brian is but in fact I have a very poor representation of David and if he
stuck his tongue out I wouldn’t be able to tell!
That’s because I’m looking directly at you Brian but when we
look directly at things that’s where we have the best visual acuity, the best
detail. It drops off very rapidly from there. We feel like we have a good
representation because we move our eyes around and we fill in the gaps like
someone doing a jigsaw, but at any one time we are seeing very little of it.
And even more extraordinarily when you make those eyes movements, when you saccade
your eyes around the world, your brain turns off visual processing so you see
nothing at all.
So if you look at yourself in a mirror and you look from one
eye to another you don’t see your eye moving because your brain is shutting it
off. So you have experiences of a smooth visual reality that is simply not
there
BC
So we are holding a 3d
model in our brains and just updating it every now and again?
SS
You’re updating it continuously yes, but you never have
access to all that information and you are guessing about what’s there if you
havent actually looked there. You could remove half the audience and replace
them with cats and I’d notice if I looked carefully but up until that point, unless
I check I won’t know
RI
You mentioned mirrors
– so how much of what we see is in terms of brain fabrication and filling in
the gaps. There’s a thing that I’ve tried where if you stare directly into a
mirror with a low light behind you and you stare directly into your own eyes - after
about 2 minutes your head seems to change. Some people will suddenly appear very,
very old. Other people see their heads pulsating, other people have this
experience where their head seems to disappear. It’s quote a buzz…
PBC
Bridget, is this the
life of a stand-up comic? Staring into your hotel room mirror for over 2 minutes
to see if your head pulsated? Or is that just Robin Ince?
BC
I think that might be where I’m going wrong. No. I don’t
tend to stare at myself – I would if it was for an experiment but I think it’s
quite an odd thing to do to stare at yourself in the mirror for ages to see if
you head starts moving.
RI
I don’t think that’s
odd at all!
SS
It happens if you stare at anything because it’s a very
unusual thing to do. What your eyes want to do is jump around the room and
explore everything so if you stare at stuff crazy stuff happens around the
edges.
RI
This is not mad is it?
This is real! David! You’re from America – this is not mad! The audience now
are staring at me so much I do feel my head is pulsating.
DE
This doesn’t rule in or out that you’re mad but it does
illustrate the very important point about the internal model – your perception
of the world has to do with this internal activity in your brain and you get
just a little bit of data dribbling in through your eyes and that little bit of
data can modulate what’s happening internally, but essentially everything
you’re seeing is happening in the closed theatre of your cranium, that’s where
the show it getting played.
So if you stop taking in information because you’re staring,
and as Sophie pointed out, your eyes want to move around and gather data, so if
you’re staring and leaving out what’s out there, your brain will start having
its own reality trip. We experience this every night when we go to bed, we have
our eyes closed and we still have a full, rich, visual experience but it’s
unanchored from any data coming in, so you go off to any reality you want. And
the really strange part is you believe whatever your brain is serving up to you.
You’re in the middle of a dream and you buy the whole thing.
PBC
And what do we know
about the physical processes that are happening in the brain, so when you’re
building this model you’re seeing the external reality what is your brain
actually doing
DE
The wrong way to think about it is that light hits your
eyes, it works its way towards the back of your brain and then up to some end
point, and then you see, like a camera. In fact it’s the opposite – your whole
visual cortex, the back of your brain, is generating this world, essentially it’s
generating hypotheses about what it expects is out there and then the little
bit of data coming in to your eyes is compared against that model, and all what’s
going back to the visual cortex is just the difference – the violation of those
expectations – what it gets wrong. That’s what’s happening. So it’s like the
system is running backwards from the way you might imagine it.
RI
Bridget. How
disconcerting do you find this idea that our perceived reality – when we look
at images - you’re not seeing anything,
we’re just fabricating this for you, for practical use, for speed, maybe to
save energy, how do you feel about that Bridget?
BC
I find it quite comforting because I’m often told by people
that I have no grasp on reality and now that I have this information, I’m able
to say to them, “what is reality?” There is no reality. What you mean to say is
you have no grasp on MY reality. What I’m really interested in since I read
David’s book is, if we can agree there is shared reality, i.e. that the things
that a lot of us see, a lot of us think are the same thing, how do two separate
individuals have a shared reality that is not based in a common reality, so how
do two different people see the same ghost?
PBC
Ghosts don’t exist… They
don’t!
BC
No, but two separate people can have two experiences that is
not a shared experience.
PBC
Of something that is
not there?
BC
Yes!
PBC
I don’t accept that!
[Audience… Ooh!]
RI
Don’t be surprised!
He’s a physicist!
DE
I can’t answer the ghost question because I’m with Brian on
this one, there’s no evidence to support that ghosts exist.
BC
I’m not saying there are ghosts, but there are people who do
believe and they are in different places.
DE
So I mentioned that your reality is constructed in this
closed auditorium of your skull but the machinery in there is shaped by your
genes and more importantly, your culture. Every experience you’ve ever had. So
if people are in a culture where ghosts exist as part of the mythology then an
interpretation of some external stimulus will naturally be interpreted in that
framework. And it’s not surprising if several people in the same culture will have
the same interpretation because of their shared history.
SS
And you find that with people saying I’ve toasted this piece
of bread and I’ve seen a figure of the Virgin Mary in it – that never happen to
people who are not already religious. It simply doesn’t happen. So you are
over-interpreting something that is clearly there but it looks like something
to you.
DE
I usually see brains in toast
RI
My bagel has Richard Dawkins
in it. “Don’t eat me!”
SS
But it only happens if you already believe in the larger
phenomena. So atheists don’t find pictures of Jesus in toast - it doesn’t
happen. It’s driven as David said, but their expectations and their beliefs are
feeding in to this. Perception is highly interpretive. It’s not sitting around
going “what’s going on, let’s have a look…”
It’s going “Oh is that a cat? Is that a ghost? Is that Jesus?”
DE
I just want to question how much is actually shared. So, we
can transact in the outside world with the colour red, if I say “pass me the red
thing” you will sort of know what I’m talking about, but beyond that, language
is really low bandwidth and it doesn’t represent something that’s truly shared.
So if I say “justice” that means something in my head and something in your
head too and everyone has a different entire history of what that word might
mean, and this is true of every word in our language. I think when we draw the
diagram of overlap there’s not that much overlap between people perhaps.
RI
In terms of within human cultures, what is the
greatest disparity we see in different cultures in realities? We often hear time
being used, different groups or different tribes, will have a different sense
and feeling of the past and the future and the way that it is expressed.
SS
You definitely do find it. You can find differences actually
in colour depending on whether or not you have words in your language for
colours. So we only relatively recently got a word for orange - before then
everything was red or yellow. And you can find environments where people speak
a language that doesn’t have particular colour words, and they just don’t see
colours that way, they describe a different spectrum. They are seeing the same
world as you, but they are really not, at some level, seeing the same thing,
and the argument is that language moderates that.
To go back to David’s point, you can consider language to be
a map of the world and you fill in the details that you need. We kind of get by
with a map that works for everybody, but say you want to learn a skill, be a
wine taster or a doctor, you start learning new words to describe the
perceptual stuff you need to know to do that. Any kind of expertise involves
new words and new mappings.
You also find difference in emotional experience so you can
find emotions that are expressed similarly across all human cultures, like
laughter, and you also find other emotions that are extremely culture specific.
For example there is a kind of mad fear associated with a particular Inuit
culture where people go completely wild with fear, and they run around and they
tear off their clothes and eat faeces and they steal things and then they go to
bed remembering, absolutely nothing.
Now, we don’t have that construct of fear in our culture and
we, on the whole, tend not go crazy, steal your things and eat faeces. We don’t
do that. It’s an extreme example but there are other kinds of strong emotional
experiences that are so culture specific it suggests there is not some
universal experience.
PBC
David. Given that there’s
a strong cultural element to the way we perceive the world and we’ve also heard
that language plays a role, the language that you grew up with and learned
determines your external model, how much of that model is innate, hard wired
into the brain? And how much of it is learned and dependent on the culture that
we grow up in?
DE
Much of it is shaped by the culture you happen to drop into,
so one example is language. Babies are born able to hear any of the sounds of
human languages, but as they are exposed to their native tongue, their map of
sound space gets crafted, gets put into shape, so that they get really good at
hearing particular sounds, and they become unable to hear other sounds. So for
example a baby born in Japan can hear the difference between “R” and “L” sounds
but as the baby gets older he or she loses the ability to discriminate those
sounds. And so this is an example of being born sort of universally able to
take in whatever the world is going to offer, and then the world shapes us and
crafts us.
RI
Is that neural pruning?
So we actually lose, but we gain more connections?
DE
Yes, you are actually getting more and more synapses during
your first year (synapses are connections between specialised cells of the
brain - the neurons) and you get more and more until by the time you are two
years old you will have more than you will ever have in your life. Then it’s
all about pruning back that overgrown garden, and that pruning is essentially a
Darwinian process – whatever is resonating with the world and getting used
stays around and gets strengthened, and the other stuff goes away.
PBC
I would imagine if I
met a tribe that had never encountered anyone from outside their particular
area before, I would imagine that I was looking out on the same world as them,
I see the world in the same way. But are you suggesting that really that is not
necessarily the case?
DE
Yeah, it’s all about your interpretation and their
interpretation. So you would see something in the artwork that they show you
that they don’t see and vice versa. I think what’s more interesting than cross
cultural differences in reality are the differences we see within a culture. So
for example, 1% of the population has schizophrenia and when someone is in the
thick of a delusion, the same photons are hitting their eyes as yours, the same
scene is hitting their eyes but they have a completely different interpretation
of what’s going on. 3% of the population have synaesthesia which is a cross
blending of the senses, so they might hear music and it causes them to see
colours, to physically have a colour experience. So they are having a different
experience of reality than you are. And even within your own life, moment to moment,
you can have different interpretations.
I was hiking in Colorado a while ago and I was told by a
guide, “By the way, there are a lot of bears around here.” So then every shadow and movement I saw after
that I thought was a bear, because my interpretation of the world had a
different frame. So everything about how we perceive an object is about “us”,
it’s about our unique, historical trajectory… what has crafted you from the
moment you dropped into the world, your family of origin, your neighbourhood,
your culture & experiences
PBC
Sophie. Why is our
model of reality so subjective? Clearly the ability to build these
sophisticated models of reality is Darwinian, it’s evolved. So why is there this
element of cultural subjectivity?
SS
A certain amount of it is likely to be there because we all
share broadly similar physical forms – we live in a world with the same
physical properties, so even if you go to a culture that’s never seen a white
European person before, things still drop down when they let go, they are born
and they die and they have arms and legs and move the same way. So there are
certain general constraints that come from the physical world that are there
for everybody. Beyond that, because one of the characteristics of the human
brain is its sheer size and plasticity and flexibility, and clearly we solve
the problem of perception in a number of different ways, perception isn’t only
one thing.
If you look at my area of how people hear voices – when you
hear voices the left side of the brain and the right side of the brain do
different things with the same information, then later on they put it together,
so when you encounter someone you know, they are easier for you to understand –
that’s the outcome. But before that, there’s been a lot of separate processing
of stuff.
And you’ve got no insight into that, but it’s just the way
that the brain has carved it up. So there’s constraints based on the physical
nature of life, and constraints based on how the scale of the possibilities
that the brain can solve the problem. Beyond that, we all have entirely
different developmental trajectories.
Do you remember when everyone was very concerned about
clones – wouldn’t it be awful if you had a clone just like you? No! That can’t happen. You’d have to raise
that clone for 20 years before they were remotely like you so you’re not going
to have a clone catching up on you and being just like you, because their
experiences will be different. We have these large brains and the
characteristic of mammal’s brains is that they are big, and we have extended
juvenile periods when we train these brains up, and we don’t all have the same
experiences during that training. It’s a huge amount of time when your brain is
developing during juvenilia and that gives you considerable plasticity and
flexibility in the finished product, not that there ever is a finished product
because it changes through your whole life span
PBC
David. We are hearing
Sophie describing the complexity of understanding language and there are lots
of different bits of the brain putting this data together, and at some point
you understand the language. You mentioned the complex visual system – it’s
remarkable that we manage to build this synchronised model of reality from all
these inputs. We don’t have a lip synch problem, we see people’s lips moving,
we interpret that, we hear sound and we interpret that, we put it all together
and we get this in-synch view of reality. Do we know how that happens?
DE
You’re pointing to a very interesting issue which is that
the different senses will process data at different speeds. So for example the
reason that we use a gun to get sprinters off the blocks is because you can
react faster to a bang than you can to a flash of light. It’s much slower when
signals have to come through the visual system and out through the motor
system.
We’ve known since the 1800s that the different senses get
processed at different speeds. But what you’re pointing to is that if I clap my
hands, it looks synched and it feels synched to me – I put out the motor
command and I hear it and feel it and see it all at the same time, Your brain
is doing lots of sophisticated editing tricks to make that seem true and the
only way it can pull it off is for you to live in the past. I don’t mean the
clothes you’re wearing!
So when you think the moment “now” occurs it’s already long
gone. That allows your conscious mind to put together a story of what just
happened - it has to stitch together a lot of information, compare across the
senses, and finally serve it up - and that’s the story that you have.
PBC
Do we have an idea of
what that delay is?
DE
Yes. It’s estimated to be half a second.
PBC
So how does that fit
with our ability to dodge a projectile?
DE
It turns out your unconscious brain - which accounts for
most of what your brain is doing - can do extremely sophisticated things. So
for example, people hit fastballs in baseball all the time, those are
travelling at 90mph – the ball travels from the pitcher’s mound to the home
plate in 4/10 of a second, which is faster than your conscious mind can keep up
with. I used to play baseball and my experience was always becoming consciously
aware that I had hit the ball and it was flying away, and now it was time to
throw the bat and run, because your body can do incredibly complex things
pre-consciously and often without conscious interference at all. And as we
automate things – ride a bike or walk or eat – you don’t even have access to
how you’re doing it but none the less your brain can take care of it.
PBC
So that means if a
baseball is coming towards the bat, that timing of the hit which we can time
very accurately, that’s unconscious. It takes precedence – your brain
prioritises that information… do this first and I will build the model of
reality and experience afterwards.
DE
Exactly. There are shortcuts where you can have visual
information coming in, making decisions, hitting the motor cortex, signals go
down your spinal cord to your muscles, you’re making feedback corrections on
the swing… all of that happens – and this underscores the point that putting
together the story of your conscious experience is a separate process that’s
very slow.
BC
I once had some really good advice from a farmer. We were clay
pigeon shooting and I kept missing and he said, don’t think about it, don’t
look at the clay, just imagine where you think the clay is going to be, and
then aim much further than that. And once I did that, I didn’t miss a single
clay. Literally when I stopped thinking about where it was and hitting it, and
went way in front of it… it is interesting that with target sports you’re kind
of not supposed to look at the thing you’re trying to hit.
PBC
That happened to Luke
Skywalker in Star Wars didn’t it? When he had to fire the thing down the death
star.
RI
You are such a physicist!
DE
This illustrates an important point. The conscious mind typically
only makes things worse when something is automatized and the body can just do
it. Try an experiment. Pick up two pens and sign your name forwards and
backwards, in a mirror image, so your left hand is doing backwards from what
your right hand is doing. It’s easier to
do if you don’t think about it. The moment you start to think about how the
letters look, you can’t do it any more.
BC
Same as when you’re coming down the stairs
DE
Yes. Same as playing the piano. If you think of how you are
doing it, you can’t do it.
RI
When you talk about
the human brain and its malleability and learning, I was thinking of the Sperry
experiment where there’s a frog which requires a certain line for a fly to go
past for the tongue to hit and catch the fly. The frog is not thinking
consciously about it. Sperry took the frog’s eye out and put it back in upside
down. What they found was the frog never learns. Every time a fly goes past the
tongue goes in the opposite direction. The frog starves to death. But we seem
to have the ability to change our behaviour to survive, but the frog couldn’t.
It died.
SS
If you go to London zoo in the reptile house, they have a
great big crocodile skull with a great big chunky plate of bone running down
his nostrils and eye holes. It’s huge and heavy, and right at the back, about
the size of my little finger joint, there’s a little pit for his brain. Now I
can laugh at his little brain but if I was in the water with that crocodile and
his little brain, he would be more of a threat to me than I am to him with my
lovely big brain, because he has a limited repertoire, but it works well.
You can’t just line up all the animals in the world based on
the size of their brains, and say at one end we’ve got simple behaviour and here
we go up through the vole, and getting more complex up to humans. It’s not that
simple. Generally in evolution we can see the step changes where we start to
see new networks getting built in, so by the time you get to primate brains you
start to see quite consistently different patterns that do seem to relate not
just to size, but to extreme complexity and perceptual processing. So for
example, mammals evolved in the dark and lost the ability to see colour. People
say “oh no no, not my cat!” but I promise you your cat can’t see colour. Us primates
rediscovered that ability to see colour. We found a way to get that
information, probably to do with fruit eating or something – but that’s an
example of a relationship between behaviour and perception and the changes in
the plasticity and capabilities of the brain.
BC
So we develop the things we need and there’s a lot of our
brain that we don’t use.
SS
No! You use all of it, all the time! You’d notice very
quickly if some of it didn’t work.
BC
Really?
I thought we didn’t use a lot of it.
RI
I think you told me Sophie, that people sometimes say you
only use 10% of your brain, so they did some research and found out it’s not
true. People who say we use only 10% of our brain are only using 10% of their
brains.
BC
So when you say we don’t see as much as we think we do, you
mean we don’t physically see as much
as we think we do?
SS
Your brain is dealing with a lot less visual information than
it feels like you’re getting, because as David says, you have an internal model
that you’re updating all the time. Terrifyingly, because you turn your visual
cortex off when you move your eyes or blink, you are functionally blind for 15%
of your day. When we’re driving or crossing the road we’re not seeing – that’s
how profound it is.
DE
It depends how you mean
it. What we always experience is our internal model of the road and so the
interesting part about our eye movements is, if you watch someone’s eye movements,
often we think it looks like a little camera, with the eyes moving around. But
if you were to take a camera and film in this jerky fashion, with the camera
jumping around, the resulting video would be nauseating. The reason why we feel
the world is stable even though our eyes are moving like a drunk person holding
the camera is because the eyes are not behaving like a camera – all they are
doing is finding little bits of data to add into our internal model. So you’re
totally right of course - while they are in movement they are not taking in new
information.
SS
They are suppressed! They are turned off!
DE
Yes, but the internal model is stable. That’s why we don’t experience
it as 15% of darkness, or blackness. Your internal model is perfectly fine, it
just means only 85% of the time are you landing on spots to pull more data into
your internal model and improve it.
PBC
David, this internal
model which is what we experience as reality, so we’ve discussed that it’s
partly the hardware of the brain, it’s partly learned, it’s partly cultural, it’s
also partly based on our memories and past experience. So what do we know about
those components? If we take memory for example, what do we know about the
contribution of our past experience to our present model?
DE
Everything about your past experience has left its footprints
in your nervous system, so that is what makes you exactly who you are at the
moment. The fact is that if you look around the room there’s a lot of variation
in people’s faces and there’s that much variation in people’s brains too.
Brains are unique and everyone’s experience of consciousness right now, is
presumably unique in the history of humankind. And it won’t last – we are works
in progress and so tomorrow it will be something different. But memory is
intertwined into that. All of your experiences are constantly pushing you
farther along on this trajectory that you’re on.
PBC
And what is it that’s
changing? Is it physical interconnections in the brain? Is there some sense
that it’s a program running like in a computer?
DE
To the best of our knowledge it’s all physical and
structural. One of the most obvious things that changes is the connections between
the neurons and the vast pattern of connections. This is summarised as the connectome - a huge map of a thousand
trillion connections that is like an extremely high dimensional fingerprint.
PBC
A thousand trillion.
That’s a thousand and 12 zeroes. So 15 zeroes.
DE
Yes. That’s how many connections you have and every one of
those is passing signals multiple times per second, every second of your life.
But here’s the thing. When you learn something new, a new skill or a new fact, there
definitely are changes at these connections but probably it goes a lot deeper
than that, all the way down into the bio-chemical cascades inside the cells,
then all the way down into the changes of the nucleus that change gene
expression. So we’ve been concentrating on the connections between neurons for a
long time because our technology allows us to put electrodes in and look at
that, but the finer and finer levels are harder to look at.
PBC
So it’s an unbelievably
complicated place the brain.
SS
If you think about how recently we’ve even been able to ask
questions about what’s inside our heads compared to how long we’ve been asking
questions about, say, the sky, it’s only about 100 years. When people got hold
of microscopes they found funny fibrous stuff in the brain (axons) and we
didn’t know about that until microscopes got really good, so we are living in unbelievably
early days when it comes to studying the brain.
RI
Well that’s all we
have time for - I’ve just looked at how we’ve done with the questions we
prepared and we’ve only got to question 3!
