Ep33 "Why do they start sprinters with a bang instead of a flash?"

Why do they use a gun at the Olympics? And why can you get off the blocks after the bang but still be disqualified for jumping the gun? Few things are as bizarre as our time perception. From sprinters to basketball players, from Kubla Khan to Oppenheimer, from television broadcasting to hallucinations, Eagleman unmasks illusions of time that surround us. Why does the brain work so hard to pull off editing tricks? And what does this tell us about our perception of reality?

Episode Transcript

Speaker 1 (00:04):
Why do they use a gun at the Olympics to
start sprinters? Why not use a flash of light? And
by the way, how can a sprinter come off the
blocks after the starting gun but still get disqualified for
jumping the gun? Or here's another question. If you watch
someone dribbling a basketball, it looks like when the ball

(00:26):
hits the ground, the sight and the sound are synchronized,
and if you back up a ways, it still looks synchronized.
But when you get to a very particular distance one
hundred and ten feet, it suddenly goes out of sync.
Why and what does any of this have to do
with Robert Oppenheimer, or television broadcasting, or the Emperor Kubla

(00:48):
Khan or schizophrenia. Welcome to Inner Cosmos with me David Eagleman.
I'm a neuroscientist and an author at Stanford and in
these episodes we sail deeply into our three pound universe
to understand why and how our lives look the way
they do. Today's episode is about time perception, which is

(01:17):
an area that I've studied in my lab for years.
For example, my first episode was on what happens when
an event seems to go into slow motion? When you're
in fear for your life. But today we're going to
talk about a different aspect of time. And specifically, what
we're going to talk about is that you have a
three pound mission control center that sits in darkness and

(01:40):
silence and has to figure out the timing of events
in the outside world. But this is a massive challenge
because signals stream in through different senses at different rates,
and we'll see how and why your brain works so
hard to pull off editing trail to get the timing right.

(02:03):
I recently saw the movie Oppenheimer, and if you haven't
seen it yet, you should. It's terrific. It's about J.
Robert Oppenheimer, who led the Manhattan Project to build the
first nuclear bomb. As you may know, the first test
of the nuclear bomb was in the middle of New
Mexico in a place called White Sands, which is a
big empty area. They weren't sure if the nuclear bomb

(02:25):
was going to work, because, as Oppenheimer often said, theory
takes you only so far. So after four years of
work and two billion dollars and hundreds of people on
this project, they were finally going to get a chance
to test the first ever nuclear bomb, to see if
this idea was going to work as the equations predicted.

(02:49):
So they set up the spot where the bomb would
be set off, and then they set up a few
observation sites, with the closest one being ten miles away
from the explosion. So in the movie we witness a
reconstruction of this scene, and it's tense because this is
the culmination of years of work, and this is the

(03:11):
project that might turn the tide of a world war,
and this is gonna be the first time to get
to see if it works. So the countdown clock begins,
and Oppenheimer and the rest of the scientists put on
their goggles, and finally the clock hits zero and the
detonation button is pressed and they watch this giant, white

(03:33):
and red pillar of fire reach up into the heavens.
And in the movie it's silent. You just hear their
heavy breathing as they watch this massive mushrooming cloud of
incendiary flames, just silence. We see the explosion, but we

(03:54):
hear nothing, and after about fifty seconds of this, suddenly
we the audience hear a massive shaking boom. So after
the movie, I was talking with a friend and he
hypothesized that the director had done this for cinematic effect.
The long drawn out silence was done so we could

(04:16):
appreciate the terrifying success of the race to build a
nuclear bomb. But I pointed out this was not a
cinematic effect. This is how it really was and how
it had to be because light travels ten miles very fast.
It only takes about point one seconds for the light

(04:38):
to travel from the bomb to the observation station ten
miles away. But in contrast, sound travels about a million
times more slowly. Because remember sound is just traveling by
pushing around the molecules in the air, compressing them together
and pulling them apart. And so how long does it
take sound to travel one mile About five seconds. So

(05:04):
for the folks at the observation station ten miles away,
the nuclear explosion was silent for fifty seconds, fifty seconds
of watching the most terrifying destructive force humans had ever
made in total silence. And this is also what it
was like for victims on the ground in Hiroshima and Nagasaki.

(05:28):
People who were one mile away from ground zero saw
the mushroom cloud but experienced silence for five seconds, or
if you were across town twelve miles away. You'd have
a full minute of watching what must have looked like
a colossal monstrosity that reached the sky, but it must

(05:49):
have felt the way it does to watch a television
with the sound off for a full minute. And of
course you know about this delay between light and sound
because of watching lightning, which is followed only later by
the thunder So it takes five seconds for sound to
travel a mile, So if you count ten seconds after

(06:09):
the lightning, that means it's two miles away. Okay, so
there's this difference between the speed of light and the
speed of sound. But we're about to see something very weird,
which is that, unless we're watching something like a bomb
or a thunderbolt, we don't perceive those time differences. Why
don't we perceive these normally? Since sound is a million

(06:32):
times slower, why doesn't someone talking to you from across
the room look like a badly dubbed film. After all,
the sight of their mouth and the sound of their
voice arrives at different times, just like the bomb or
the thunderbolt. And we're generally very sensitive to small differences
in timing. So why can't we pick this up? So

(06:53):
to reach our arms down into this problem. I'll give
you a do it yourself demonstration that will unmask for
you the deep weirdness of how much your brain constructs
your reality. So watch some kid dribbling in basketball. It
will seem like as the basketball is hitting the ground,
the sight and the sound of that are synchronized. Now

(07:15):
what you do is you start backing up. So you
back up, you back up. They're dribbling, You're watching them,
and it seems synchronized. The more and more you back up,
it still seems synchronized until you hit one hundred and
ten feet and then it doesn't seem synchronized anymore. Then
suddenly the sight and sound seem off. The basketball visually

(07:38):
hits the ground and then you hear the thump. It's asynchronous,
like the badly dubbed movie. So what is going on here?
Strap in, because we're about to see some things that
will blow our minds, specifically, how much editing work your
brain does behind the scenes to try to fix timing
across the senses until the difference is simply too great

(08:01):
and it says, okay, forget about it. So let's zoom
out for a minute and consider the big picture. Of
what your brain has to do. Your conscious perception requires
the brain to compare different streams of sensory data against
one another. You've got these different channels of information coming in.
You've got vision, hearing, touch, and so on, and your

(08:23):
brain has to put these together to make a big
picture of what's happening. But there's something which makes this
a really big challenge, and that is the issue of timing.
All of these streams of sensory data are processed by
the brain at different speeds. So think about sprinters at
a racetrack. It appears that they get off the blocks

(08:45):
the instant the gunfires, but it's not actually instantaneous. If
you watch them in slow motion, you'll see this sizeable
gap between the bang and the start of their movement.
It's about one hundred and sixty millisecond because it takes
time for signals to move through the brain, for the

(09:05):
bang of the gun to work its way through their
auditory system and over to their motor system and then
down the spinal cord into the leg muscles and launched
them off the blocks. In fact, if they move off
the blocks before that duration, they're disqualified because they've jumped
the gun. Because racing commissions know that this signal transmission

(09:28):
takes time, so the rule is that if you move
within one hundred milliseconds after the gun, you are disqualified.
This came up in July of twenty twenty two when
a hurdler named Devin Allen got off the starting blocks
too early. He didn't go before the gun went off,
he went after the gun went off. But he launched

(09:50):
at ninety nine milliseconds after the gun, and even for
a great athlete like him, this is below the possible
reaction time, and there was a storm of activity on
social media. But the fact is that one's reaction time
can't be that rapid. Athletes trained to make their gap
as small as possible, but their biology imposes fundamental limits.

(10:14):
The brain has to register the sound and then send
the signals to the motor cortex and down the spinal
cord to the muscles of the body. Now, in a
sport where thousandths of a second can be the difference
between winning and losing, that response seems surprisingly slow. So
could the delay be shortened if we used, say, a

(10:36):
flash instead of a pistol to start the racers. After all,
light travels faster than sounds, so wouldn't that allow them
to get off the blocks faster? For my television show
The Brain, I went to the track and I invited
some fellow sprinters so we could all put this to
the test. So, in one condition, our sprint was triggered

(10:57):
by the gun. In a second condition, we were triggered
by a flash of light. And we filmed this in
super slow motion so we could compare what happened in
the two conditions. When we were triggered by the bang
of a gun, we got off the blocks at about
one hundred and sixty milliseconds, but when we were triggered

(11:18):
by the light, we got off the blocks more slowly,
with a longer delay, about one hundred and ninety milliseconds.
Now that seems to make no sense given what we
just talked about, with light moving a million times faster
than sound. So what gives here To understand what's happening?
We need to look at the speed of information processing

(11:40):
on the inside. Visual data goes through more complex processing
than auditory data, so it takes longer for signals carrying
the flash to wind their way through the visual system
then for bang signals to snake their way through the
auditory system, so light takes longer to trigger a motor response,

(12:04):
and that's why a pistol is used to start sprinters. Now,

(12:26):
scientists can prove this by putting electrodes in the auditory cortex,
which responds to the bang, or the visual cortex, which
responds to the flash, and you can see that the
speed of the brain response is faster for the bang.
But here comes the big mystery. Clap your hands in
front of you. It looks synchronized. Well, that makes no

(12:50):
sense because we just saw with the sprinters that your
auditory system processes information more quickly than your visuals. So
why aren't you seeing the sound and the sight out
of sync. The answer, as we'll see in a moment,
is that even though part of your brain gets the

(13:10):
information before another part, your consciousness goes through a lot
of trouble to sync things up. Your perception of the
outside world is the end result of fancy editing tricks.
The brain hides the difference in arrival times, and I'll
explain to you how it does this, but first I'll

(13:31):
give you a couple more examples. So let's step back
seventy years to the early days of television broadcasting. The
engineers realized they could be a stream of sound information
and they could be a stream of visual information. But
they were worried about how they could broadcast both the
sound and the visuals and keep them synchronized with one another.

(13:54):
And what they realized, quite accidentally, was that they don't
actually need to keep them perfectly synchronized. As long as
the sound and the visuals arrive to the viewer within
about eighty milliseconds of each other. That's about a tenth
of a second. Your brain does all the work of
synking these up. And if you've ever seen a movie

(14:16):
that seems out of sync, it means that the audio
and the video were more than eighty milliseconds away from
each other, because your brain can't tell the difference. As
long as they're within eighty milliseconds of one another, it
seems perfectly synchronized to you. And this allows us to
understand what's happening. When you're watching the kid dribbling the basketball.

(14:38):
It seems that as the ball is hitting the ground,
everything is synced all the way until you back up
to one hundred and ten feet and then it's not
synchronized anymore. Why well, one hundred and ten feet is
where the speed of light and the speed of sound
are reaching you at over eighty milliseconds apart. So when
they reach you at that timing apart from one another,

(15:01):
your brain can't sync it up anymore. But as long
as they're within that window, your brain has no problem saying, oh, okay,
those belong together, I'm gonna synchronize that. So this is
the question I turned to some years ago. If the
brain is getting all this information at different speeds, how
does it know how to synchronize things in consciousness? And

(15:23):
I just want to make clear how challenging this is
if you're living in the dark inside the skull, because
these timing difficulties aren't even restricted to hearing and seeing.
Every type of sensory information takes a different amount of
time to process and to complicate things even more, even
within a sense, there are time differences. For example, a

(15:45):
bright flash moves through your retina and gets to your
brain a full eighty milliseconds before a dim flash, or
as another example, it takes longer for signals to reach
your brain from your big toe than it does from
your knows So how does your brain solve all of
this temporal smearing of information. The only possible answer is

(16:09):
wacky and somewhat mind blowing. Your brain has to collect
up all the information from all the senses before it
decides on a story of what happened. And that means
your conscious perception is actually a delayed version of what's
happening in the world. So when you clap your hands,

(16:33):
your brain gathers the auditory information and the visual information
and the sensory information of your hands touching, and all
these stream in at different times, and then it puts
together its story of what just happened, and it puts
together what should go with what. And I'll explain in
a second how it does this. But the key thing

(16:53):
I want to make clear right now is that in
order to synchronize everything, you have to wait for all
of the information to arrive. And the strange consequence of
all this is that you live in the past. By
the time you think the moment occurs, it's already long gone.

(17:14):
When you perceive the clap, it's already over. Your perceptual
world always lags behind the real world. So think of
it this way. Your perception of the world is like
a live television show. Think of something like Saturday Night Live,
which is not actually live. Instead, those shows are aired

(17:36):
with a delay of a few seconds in case someone
cusses or falls down or has a clothing mishap. And
so it goes with your conscious life. It collects a
lot of information before it goes live, so there's an
unbridgable gap between an event occurring in the world and
your conscious experience of it. So that's why your brain

(17:59):
can sync the television audio at the video or the
basketball thump with the visual of it hitting the ground
or whatever. I need to emphasize that what we're talking
about here is conscious awareness. You can see from pre
conscious reactions that your motor system doesn't have to wait
before its decisions. For example, you can duck out of

(18:21):
the way of a swinging tree branch before you become
consciously aware of it, or you can start jumping when
there's a loud sound before you're consciously aware that there
was a sound. Your body always tries to act as
quickly as possible, even before the participation of awareness, but
your conscious perception takes its time. Now that raises a question,

(18:45):
what is the use of perception, especially since it lags
behind reality and it's retrospectively attributed, and it's generally outstripped
by these automatic, unconscious systems. The most likely answer is
that your perceptions are like objects that your cognitive systems
can work with later. So it's important for the brain

(19:08):
to take sufficient time to settle on its best interpretation
of what just happened, rather than stick with its initial
rapid interpretation. Its carefully refined picture of what just happened
is all that it's going to have to work with later,
so it invests the time. So this brief waiting period

(19:30):
before consciousness, this is what allows your sensory systems to
discount the various delays imposed, But it has the disadvantage
of pushing your perception into the past. Now, there's a
distinct survival advantage to operating as close to the present
as possible. An animal doesn't want to live too far
in the past. Therefore, it may be that a tenth

(19:52):
of a second window is the smallest delay that allows
higher areas of the brain to account for the delays
create in the first stage of the system while still
operating near the border of the present. Among other things,
this strategy of waiting for the slowest information to arrive
has the advantage of allowing object recognition to be independent

(20:16):
of lighting conditions. So I mentioned a minute ago about
bright and dim flashes moving through the system at different speeds.
So imagine a striped tiger coming toward you under the
forest canopy, and he's passing through successive patches of sunlight.
Imagine how difficult recognition would be if the bright and

(20:37):
the dim parts of the tiger caused incoming signals to
be perceived at different times. You'd perceive the tiger breaking
into different space time fragments just before you became the
tiger's lunch. Somehow, the visual system has evolved to reconcile
these different speeds of incoming information. After all, it is

(20:59):
advantageous to recognize tigers regardless of the lighting conditions. Now,
this hypothesis that the system waits to collect information over
the window of time that it's all streaming in this
supplies not only to vision, but more generally, to all
the senses. So, for example, my lab measured that in

(21:20):
vision you wait at least a tenth of a second,
But the size of this window might be different for
hearing or touch. If I touch your toe and your
nose at the same time, you will feel those touches
as simultaneous. And that's really surprising, because the signal from
your nose reaches your brain well before the signal from
your toe. Why didn't you feel the nose touch when

(21:43):
it first arrived. Did your brain wait to see what
else might be coming up the pipeline of the spinal
cord until it was sure that it had waited long
enough for the slower signals from the toe. Strange as
that sounds, that might be correct, and it may be
that for a unified sensory perception of the world, you
have to wait for the slowest overall information to get there,

(22:07):
and given conduction times along whims, this leads to my
strange but testable hypothesis that I mentioned in episode thirteen,
which is that tall people may live further in the
past than short people because they have to wait for
the signals all the way from their toes before they
put together their unified perception. Okay, but how does your

(22:33):
brain know how to put all these signals together? So
to think about this, let's turn to the Mongol emperor
Kublai Khan, who ranged from twelve sixty to twelve ninety four,
and founded the Yuan dynasty. Now he had conquered the
largest kingdom the world had ever known. His kingdom reached

(22:54):
from the Pacific to the Black Sea, and from Siberia
to modern day Afghanis. His territory covered a fifth of
the world's inhabited areas, so it was absolutely enormous. He
situated himself in what is modern day Beijing. And the
thing to note is that this was back in the

(23:14):
day before iPhones and telegraphs and trains or email or
anything like that. And so the question is, how in
the world could Kubla Khan know his own empire. There's
no way he could travel even a tiny fraction of
a territory that large in his entire lifetime. So how

(23:35):
could the Great Khan know what his empire contained? The
answer is he hired emissaries like the Venetian traveler Marco Polo,
and these people would travel out to the distant reaches
of his empire and they would convey news back to
him about what was going on in the empire. And
he hired many emissaries that would go out in different

(23:57):
directions and bring news back to him about what was
going on. Now, I've never heard a historian talk about this.
But I imagine the Great Con must have faced a
tough problem what events in his empire occurred in which order.
Because of wars and weather and other issues, people might

(24:18):
travel at different paces, so the different emissaries would come
back to him at different times. One emissary comes back
and reports that a war has just ended, and another
emissary comes back and reports that a war has just begun,
and they're talking about the same war. But they got
back to the capitol at different times. And so the

(24:39):
question is how did the Great con synchronize all these signals.
The thing I want to make clear is that the
timing problem Kubla Khan had is the same problem the
brain has, which is to say, it's getting all these
different streams of information that come in at different paces.
And because your brain is locked up in the dark

(25:01):
tower of the skull, its only contact with the outside
world is via the electrical signals exiting and entering along
the highways of nerve bundles. So you've got touch information
streaming up the body, You've got auditory coming in, you've
got visual information coming into the brain. But the issue
is that all of these things get processed by the

(25:22):
brain at different speeds and at different places in the brain.
So your brain faces this enormous challenge how to stitch
together the incoming signals in the best way to make
a story about what just happened in the outside world.
For example, as we just saw, when I clap my hands,
the auditory signals get processed first, then the visual signals,

(25:43):
and yet they seem synced up. What this tells us
is that the brain is somehow pulling off major video
editing tricks, and we're going to find out how. Now,
my lab has studied this for years, and the first
thing to appreciate is that your brain doesn't figure this
out pass. It does this by involving your own actions.

(26:04):
Your own actions are the secret to understanding how everything
gets synchronized. And what I've proposed is that your brain
goes through so much trouble to get all this timing
right because of one issue causality. Because one of the
most fundamental things that any animal does is figure out

(26:25):
whether it was the one that caused something or not.
And fundamentally judging what caused what requires looking at the
order of events. So imagine you're walking in the forest

(26:55):
and you make a step and you hear a twig crack,
you can assume that was me because of you. But
if you hear the twig crack just before you land
your step, then you'd better be worried about a mountain lion.
So causality requires a temporal order judgment, which is to say,

(27:16):
did I put out the action and then I got
sensory feedback, in which case I'm going to take credit
for having done that, Versus I got sensory feedback and
then I did some action, in which case I'm not
taking credit for that. I had nothing to do with that.
And what we're often talking about is tens of milliseconds
one way or the other as the only difference between

(27:37):
these scenarios. But animals are very sensitive to this, and
at bottom, this is the challenge that animals have to
figure out. And as we've seen, the reason this is
really difficult is because the speed of sensory signals differs
and also they can change. So, for example, when you
go from a bright outdoors into a dimly lit room,

(28:01):
the speed at which your eyes are talking to your
brain slows down by quite a bit. And what that
means is that now your vision and your motor actions
are out of sink a little bit. So if right
when you walked into the dim room, I threw you
a ball, you'd probably miss it. I don't know if
you've ever played volleyball right when the sun's going down,

(28:22):
but everyone's having good time, and then right as the
sun's going down, everyone starts getting hit in the face
with the ball and so on. Because what's happening is
your time is getting out of sync. Now, now that's
an example of a short term fast change, but on
a longer time scale, as you grow from a baby
to an adult, it takes a longer time to send

(28:44):
signals out to your hand and get signals back. And
so all of this led me to think a while ago,
somehow the brain is having to figure out what its
expectations are. It's having to modulate on the fly how
long it expects for signals to come back. And so
I hypothesize that the brain is always doing this on

(29:06):
the fly. It's always recalibrating, it's readjusting the expected time
that it takes for signals to come in. But how
does it do that? And the answer is by interacting
with the world. Because whenever you touch things, or you
kick things, or you do anything like that. Your brain
is saying, okay, everybody, synchronize your watches. I'm putting out

(29:29):
an action, and what I expect is that I'm going
to see it and hear it and feel it all
at the same time. That's the prior expectation that it
comes to the table with. And if I hit the
table and it goes hit knock like that, my brain
will adjust the timing. In other words, your brain doesn't
know in advance how long your limbs are, or what

(29:52):
the lighting level is, or how fast sound travels and
so on. It just figures out what it needs by
reaching out and interacting with the world. It just needs
to embed the single assumption that if it sends out
an action such as a knock on the table or
a clap of the hands, all the feedback should be
assumed to be simultaneous, and any delays between the senses

(30:16):
should be adjusted until simultaneity is perceived. In other words,
the best way to predict the expected timing of the
signals is to interact with the world. Is to go
out and touch and kick and push and knock on
the world, and your brain makes the assumption that all
the feedback is simultaneous. The best way to predict the

(30:38):
future is to create it. You cause something and all
the consequences should be synchronized. That's how you keep yourself calibrated. So,
just to be clear, what this suggests is that if
the feedback signal arrives with a delay, the brain's going
to adjust things to make it seem like it happened

(30:59):
close in time. So I took this hypothesis and in
my lab we created a very simple experiment. You come
into the lab and you're seated in front of a button,
and whenever you hit the button that causes a flash
of light. You press the button, the light flashes, But
then we sneakily inject a small delay in there, let's

(31:21):
say one hundred milliseconds. So you hit the button and
then the flash of light appears. What happens very quickly
is that your brain adjusts to the delay. Because you're
the one causing it, the button and the light are
interpreted as simultaneous, or at least close to simultaneous. So

(31:42):
after just a couple of hits, it doesn't feel like
one hundred millisecond delay. It feels like the button pressed
and the flash are happening at the same time. Why
it's because your brain is the one putting out the action,
so it knows what to expect. And then we pull
the big trick on you after your brain is used
to this delay and thinks this is simultaneity. Now you

(32:06):
press the button, and we make the flash happen immediately,
no delay. And what is your perception? You think that
the flash happened before you hit the button, So you
hit the button, the flash occurs immediately, and you say, WHOA,
I didn't do that. It flashed just before I hit it. Now,

(32:27):
this is amazing to witness because this is an illusory
reversal of action and effect. You hit the button, but
you believe the consequence happened before your action. Your brain
gives you the wrong answer because it has adjusted it
expects a certain delay, and now we've tricked it. Now,

(32:48):
this is a very simple experiment that you can reproduce
at home with a little bit of programming, but it's
a really big deal because it demonstrates that the timing
you perceive in the world is not what it's truly
happening out there, but an easily manipulated story put together
by your brain now. I presented this research at a

(33:08):
university recently, and a professor there came up to me
afterwards and asked me about something. He said, they just
got a new telephone system installed and he types at
his desk all day and sometimes he turns to the
phone and dials the number, and his impression was that
the line starts ringing just before he hits the final number. Well,
I immediately understood what was happening here, although he wasn't

(33:32):
aware of it. His computer keyboard has a delay between
hitting the key and a letter appearing on the screen.
Typically for computers that's about one hundred milliseconds, but we
never notice it because we calibrate to the delay. Anyway,
he now turns to the phone, and this new system
has a much smaller delay. So when he hits the

(33:53):
final number on the phone, the ringing starts, but it
feels like it happens just before he hit the final
number key. He's experiencing this illusory reversal of action and effect,
and it's because the delay of the two machines is different.
He's calibrated to one, and suddenly the delay is different

(34:14):
on the other. And by the way, you can turn
this into a game of sorts. My graduate student John
Jacobson was inspired by this discovery to program an unbeatable
game of rocks, as or paper. So here's how that goes.
There's a countdown and then you hit a key to
register whether you're throwing a rock or as or a paper,
And just like in the game, the computer presents its

(34:36):
choice at the same time, or so you think it's
actually waiting one hundred and fifty milliseconds and seeing what
you did, But it feels simultaneous to you because your
brain adjusts to you pressing the button and you're seeing
the result on the screen. And then every once in
a while the delay gets dropped, so it feels like
the computer answered before you, even though it was again

(34:58):
just registering your press and reacting immediately. You have the
feeling that you reacted after it and that you answered
exactly the wrong thing. And by the way, I'll just
mention that my students and I ran a bunch of
experiments in which we showed that this temporal recalibration can
last through time, which, as you may remember from episode

(35:19):
twenty four, is exactly what happens with the motion after effect.
When you say, watch a downward waterfall for a while,
and then you see everything moving upward. It turns out
if you watch the waterfall and close your eyes and
then open your eyes later, the illusion still happens. And
without going into details, this indicates the mechanism by which

(35:42):
the active recalibration happens under the hood in the neural circuitry. Anyway,
my lab published some years ago a model in which
recalibrations of motion are exactly the same mechanism as the
recalibrations in the time domain. In other words, words, this
suggests the possibility that the brain uses exactly the same

(36:04):
circuitry for time and space. I'll skip the details here,
but for interested parties, I've linked to the paper at
eagleman dot com slash podcast. Okay, so we can show
that the brain constantly recalibrates its timing. But remember this
isn't just a party trick of the brain. It's critical

(36:24):
to solving the problem of causality. The only way this
problem can be accurately solved in a brain with lots
of senses where timing is always changing is by keeping
the expected time of signals actively calibrated so that you
can determine before and after, even with these different sensory pathways,

(36:45):
so your brain's always making this adjustment. But here's something
really important. Let's return to what we saw with this recalibration.
A person hits the button, but if we've just removed
the delay, they say, WHOA, that wasn't me. The light
flashed before I did anything. And that got me thinking
about something because I realized I had seen that kind

(37:08):
of reaction before. So when I saw participants saying that
wasn't me, I thought that looks really familiar. Specifically, this
is called credit misattribution, and this is where you cause
something but you deny that you were the one who
did it. And this is one of the striking symptoms
that we see in schizophrenia. A person suffering from schizophrenia

(37:32):
will often do something and not take credit for it.
They believe that it was not them who caused the
thing to happen, and then it's perfectly rational for them
to cook up a different sort of explanation for it
and say someone else is doing it, or this was
caused by a signal from a radio tower or whatever,
but it's not me that did it. Whatever's going on,

(37:54):
And so some years ago, I started to hypothesize that
schizophrenia may actually be a problem with time recalibration. What
if you're not properly adjusting the timing of your inputs
to your outputs, you would have a very difficult time
judging causality. But that's just the beginning. I immediately started

(38:16):
thinking about another symptom of schizophrenia, which is auditory hallucinations.
So here's the thing. Under normal circumstances, you're always talking
to yourself. You have an internally generated voice, and you
listen to that. And by the way, if you're thinking,
what internal voice, that's the internal voice. But what happens

(38:37):
if you get the timing wrong, even by a few milliseconds,
such that you thought you were hearing the voice just
before feeling like you generated it, you would have to
conclude that it was somebody else's voice, not your own.
And it's all simply because the timing is off between
generating the voice and listening to it. And if thinking

(39:00):
led me and my students to run experiments at a
county mental health facility with people who had schizophrenia, and indeed,
we found that people with schizophrenia do not recalibrate their
timing as well as healthy controls do. So when we
give them a test like hit the button and did
the flash of light occur before or after, and we

(39:21):
measure their recalibration, it's much less or it's absent. Now,
like all science, this is going to require many more studies,
but if this is the right way to think about schizophrenia,
it completely changes our approach to it. It means that
instead of throwing pharmacological solutions at it, which have limited success,

(39:42):
just imagine if you could give somebody a video game
that they play for a few minutes and then their
auditory hallucinations go away because we've recalibrated their timing. So
this is work I'm pursuing now, and it all began
with these very simple experiments. So to wrap up today's episode,
it's an ongoing passion of mind to figure out how

(40:05):
the brain constructs reality. And there are very few things
weirder than time. What we saw today is that to
synchronize the incoming information from the senses, our conscious awareness
has to lag behind the physical world. But none of
that is obvious to your perception. And even weirder, the

(40:26):
order of sensory events in the world is dynamically recalibrated,
so you can hit a button that causes a flash,
but under different circumstances, you'll believe that happened before or after,
and we can easily change that around. And this is
because your brain can't automatically know what the timing should be,

(40:47):
especially as sensory timing changes all the time. So your brain,
living in darkness, constantly interacts with the world to recalibrate
its timing. It says, I'm going to knock on something now.
Everyone synchronize your watches. And this matters to the brains
so much to get all this timing right, because this

(41:08):
is the basis of judging causality, and when that recalibration
isn't working well, it makes it difficult to interpret the
world as we see in schizophrenia. And this episode points
us back to a fundamental lesson that we've seen a
lot in earlier episodes, with visual illusions and auditory illusions.

(41:30):
Reality is not passively received by our brains, but is
actively constructed. Go to Eagleman dot com slash podcast for
more information and to find further reading, and send me
an email at podcast at eagleman dot com with questions

(41:53):
or discussion, and I'll be making more episodes in which
I address those. Until next time, I'm David Eagleman, and
this is Inner Cosmos.