Transcriber: Fatma Abdeldaem
Reviewer: Rhonda Jacobs Good evening, everyone. So the theme of today's event is change. Change from within, but what is the one thing
that all change needs? The one thing that
all change needs is time. Change needs time, it needs now and then. Without either of those there's no change. But what is now? And perhaps even more profound, when is now? And to answer that question,
we need to look at the brain. We need to look at time in the brain,
time in our perception, in our experience. And I think you can share with me the experience that time
in our mind, in our experience is perhaps a little bit more flexible
than time in the real world, right? Sometimes it can go a little faster,
it can go a little slower. I think we have all learned
as young kids, five, six years old that five, 10 minutes waiting
in the dentist office takes hours, whereas an hour in the playground
flies by in five minutes. So time in the brain is subject to change. Now, where does that leave us
with the question of when is now? When is now in the brain? Now, in answering that question,
I'll show you a few things along the way. I'll show you that sometimes we can be blind with our eyes wide open
and not even notice. I'll show you why it's so difficult
to hit house flies in midair, And I'll show you that
as opposed to real time, which goes only in one direction, in our brain we can actually
go back in time and rewrite history. So let's start with that moment
of blindness with your eyes wide open. This is where you can pull out
your little purple mirrors. So, I'd like to invite you to take out
your mirror and look in it. Look at your own left eye. All right, everyone doing that? Now, move your eyes
so you're looking at your right eye, and go back and forth between
your two eyes a couple of times. Once you get the hang of that ask yourself this question. Do you ever see your own eyes move? (Laughter) Well? And I think you'll find the answer's no. You don't ever see your own eyes move. Now, isn't that odd. Why is that? Why do you
not see your eyes move? Well, let's approach it from a scientist's
perspective and form a hypothesis. One possible answer is that you don't see your own eyes move
because eyes move too fast to see. Let's test that hypothesis. So now, put your mirror away,
and now look at your neighbor. So, this requires a bit of logistics. So, look at your neighbor's eyes and one of you -
you have to take turns here - one of you stare at the other person's
left eye and then look back and forth, and then the other person can have a look. Do you see the first person's eyes move? (Audience chatter) And now you can swap if you want to. (Audience chatter) Okay. (Audience chatter) So, I think we've found that when you're
looking at your own eyes in the mirror, you cannot see your eyes move, but when [you're] looking at someone
else's eyes, you can see their eyes move. So what's going on? The other person's eyes
don't move faster than yours. So, what's going on? Why can you see their eyes
and not your own? And the answer is,
for the briefest moment you are blind. When your eyes are moving you are blind,
you cannot see when your eyes are moving. But do you notice? You don't. What happens? It's not like your vision
goes black for a split second, like when you close your eyes. It's also not like
there are image stutters, like you're watching Netflix
on a bad internet connection. It's also not like
that moment of time is lost because then my voice
would be all chopped up, then parts of my sentence
would be falling away, and that doesn't happen either. So, what's happening? And the answer is there's this little gap when your eyes are moving from wherever
you were looking before to your other eye, when there is no visual input, and your brain covers it up,
it pretends it never happens, it takes what it knows from before
and after and stitches it together and pretend everything is okay. So, you were blind
for the briefest instance. Now, it actually gets a little bit
more complicated than that. Your brain takes time to do things. This is Andy Roddick. Andy Roddick was a professional baseball -
excuse me - professional tennis player. (Laughter) He was a professional tennis player, and one of the reasons
he was so good at what he did is that he had the exceptional ability
to hit that little ball so hard that it would cross
the court at 250 km/hr. That's really fast. And what does that mean
for the person on the receiving end? Now, let's just do the math for a moment. At 250 km/hr, it takes roughly
a third of a second for the ball to get to
the other side of the court. Now, this is where it gets problematic because your brain needs time to process incoming sensory
information including vision. You might think that goes
pretty fast and that's true, but this ball is also going pretty fast. So, it actually takes - a conservative
estimate - about 1/10 of a second for the brain to process
the visual information about the location
of the ball as it's flying. So, in that moment of time, The receiver sees the ball
in a particular location, it takes 1/10 of a second for his brain
to figure out, What am I seeing? It's right there. In that tenth of a second,
the ball has continued moving. Now, how relevant is this? Is this a an intellectual curiosity, these minute segments of time
that don't really matter in real life? No. In professional tennis, the ball has moved
seven meters in that time. Which means that this poor receiver is seeing the ball seven meters
behind where it actually is. Now, as impressive
as Roddick's achievements are, I think the receiver's achievement at even getting near this ball
is at least as impressive. So how does the brain do this? How does the brain manage
to interact with a ball at seven meters away
from where it's seeing it? And the answer is that
the brain predicts the future. It knows about its own delays, and tries to compensate for them
by predicting what's going to happen. And the brain can do this
because the trajectory of a ball, for a professional tennis player
at least, is fairly well established, it's very fairly predictable. But what about if that
prediction breaks down? What if the future is not so predictable? This is a common housefly. A common housefly flies at approximately
eight kilometers an hour. This is 1/30 of the speed
of Roddick's serve. So, if this thing moves so much
more slowly than a tennis ball, why is it so hard
to hit these things in midair? And the answer is,
they move unpredictably. Why is that a problem? Because your brain still has the same
delay in its own internal processing, and it tries to compensate for it. So, this housefly is moving. Your brain knows
it's behind on the real world, so it compensates for that
and predicts where the fly is going to be. It gives you a location
where the fly never goes. You see the fly where the fly never is, never will be, never was. So, no wonder you will miss it
when you try to hit it. So the prediction works sometimes,
but it also breaks down sometimes. And actually it gets even more complicated
because this delay period isn't constant, the delay is variable depending on
what sort of features were talking about. What do I mean by that? Here's a scene - there's the baseballer
I was referring to earlier. So, when you look at this scene,
you see everything together, right? You see the color, you see the motion,
you see the shape - it's one object, one person. But in the brain, all of those
features are pulled apart and processed in different
areas of the brain. More importantly, they're processed
at different speeds. So, it turns out that color is actually
processed more quickly than motion, and that, in turn, is processed
more quickly than form. So why does that matter? Well, let's see. You see this image? It comes on your retina, in your eyes,
and your brain gets to work on it, and then the color
information is extracted. Well, according to this image
not at all - there it is. It's processed more quickly
than the motion information, which, in turn, is processed more quickly
than the form information. So, one moment is spread out
over time in terms of processing, which means that at any given time, the finished information
that the brain has about the outside world comes from different pasts. It comes from different moments in time, which means even if we just sort of
put everything together that it has, what you would see is not this ...
what you would see is this. This scrambled mess where the color
is more recent than the motion, and that, in turn, is more
recent than the form. But that's not what we see, right? This is not what we experience. We see a baseballer with a color
and a form and a motion all together belonging to the same object. So how does a brain fix this? How does the brain stitch
all those features back together again? Well, one possibility
is that it simply waits. So, it sees something coming,
you get a formless color and then ... it waits until the motion
information is available, and the form information is available,
then it tells you, here's that baseballer. But if you think about it, that's a pretty
inefficient strategy, right? From an evolutionary perspective, you've
got information that might be relevant, and you just wait until
you know more about it? So imagine our caveman ancestors. They're sitting around
a campfire in the dark, and they're talking
or grunting or whatever, and at one point one of them sees motion
in the darkness behind his companion. Well, so if this caveman had this brain,
then he would do nothing with this motion. He would wait until he figures out
what the precise shape is of the thing that's coming out of the shadows
to eat his companion. This is not a good thing for this caveman. A better evolutionary brain would be to be able to act
on this motion right away. It's not important
what the shape is of that thing. He needs to be able to act on the motion
as soon as his brain detects it. So that would mean that
the color information is available to us, and then after the motion becomes
processed and the form becomes processed, then we finally know what the object is. But are we ever aware of a shapeless form
that then resolves into an object? Is that how we experience the world?
It's not how I experience the world. Or is it? Let me rephrase it more carefully. That's not how we remember
seeing the world. Now, what's the difference,
is that as it turns out we do for the briefest instant experience
a new object as a shapeless color, but as soon as the form
information becomes available, that gets added to it, and after that,
it's only that object with the form known. The original impression
of the shapeless color is gone, is wiped out, is rewritten. But that would mean that the brain
is allowed to go back in time and rewrite its history. And it turns out that
the brain can indeed do this. And here's an everyday example. I put up this clock because this is
the first time I observed this illusion. This only works for a clock
with a second hand that actually ticks, that stops and moves. And my first experience of it
was at the train station. I looked at the clock
for the first time in that sitting, and what I notice is that the first time the second hand moves
seems to last longer than the other times. Does anyone else get that? So, that phenomenon
is known as chronostasis, and in fact, you already know
why that happens. Because it's the same thing
as with the eyes in the mirror. When you move your eyes
from some other place to the clock, there's a gap in your visual input,
nothing's coming in. Your brain has a gap to fill
with information that it doesn't have. So, it takes the information
that it gets when it gets there - the clock hand
at that particular position - and backfills the history. It fills that image over
the whole history that was empty, and you get the impression,
I've been looking at this clock for ages, and it has been standing still
this whole time, and after that
it starts ticking on its way. And so that first time seems
to last longer than the later times. Your brain rewrites history, But this is only a matter
of a split second, right? And it turns out that the brain
is actually able to rewrite much larger periods of history
than just that second. And here's a cool experiment
that showed that. This is a fun experiment where
the researchers took two groups of people and told both groups of participants
that they had to do a task for 10 minutes. And in actual fact,
the first group of people, the researchers came back
into the group after just five minutes and told them the 10 minutes were up. In the second group, the researchers
came back after 20 minutes and told them the 10 minutes were up. So for one group of people,
time artificially flew. And for the other group of people,
time artificially crawled. Now, we know that time flies
when we're having fun, but can the reverse also happen, can time flying cause us to have more fun? And the answer is yes. The group who thought
the time had flown had more fun, reported enjoying the the task more than the group for who time
artificially crawled. So, where does that leave us
with the question of when is now? Coming back to this, we've seen that the now in our brain
is actually the past, predominantly. Admittedly the brain does a pretty good
job of compensating for its own delay by predicting the old future and therefore
currently the present, hopefully. It runs into problems
when the future is less predictable, so when that housefly changes direction. You end up seeing things
that never happened, never will happen, never have happened. You end up seeing different pasts
because of differences in delays. And all of this would lead to an absolutely not understandable memory
or experience of the world if it weren't for the fact
that the brain, unlike real time, is actually allowed to go back in time
and clean up its own mess. So, the brain is able
to restructure the whole story because it's allowed to go back in time. So where does that leave us with
the question of when is now in the brain? I don't know. And the one thing I do know
is that when you open your eyes - whether these beautiful
eyes or your own - when you open your eyes
and look out into the world, there's one thing that you are not seeing, and that is now. Thank you. (Applause)
