Translator: Leonardo Silva Reviewer: Rhonda Jacobs
Thanks. I'm going to be talking about decisions
and how our brain transforms them into actions.
So a decision is a state of mind
which is aiming to produce a particular action.
So let's have a look at this goalkeeper.
He's got to decide, with very little time and very little evidence,
maybe no evidence,
and he's got to make an action to dive to the left or to dive to the right.
And actually, sometimes,
he should inhibit making any action at all and stay in the middle
because sometimes that works as well,
and that's going to be important to the end of my talk.
So, what I want to do is just think about decisions and actions,
and we should remember that decision theory,
classical decision theory,
has been obsessed with whether our decisions are rational or irrational,
but whichever one of those they are,
we still have to transform them into actions.
And I'm going to think about how the brain bridges decision to action,
and I just want to try and say three things about that bridge.
So, the first thing that I would like to say
is that we can't really trust our subjective experience
of our own decisions.
The way we think we decide is radically different
from the way the brain actually decides for us.
Here's a modified version of an experiment that was done recently in Sweden,
which makes this point rather nicely.
The experiment's very simple.
The experimenter shows two pictures of two different cars
to the participant in the experiment,
and the participant simply has to choose to decide which car they prefer,
and they indicate that by pointing towards one of the cars.
The experimenter then takes both of the pictures away
and then re-presents the car that the person had chosen
and asks them to explain their decision.
Now, I'll just back up a little bit.
Look at those two cars.
You choose which one you want.
And then, you have to explain your decision.
But the experimenter's a magician,
and you may have noticed he's actually swapped the two cars,
because he has a picture of the other car which you didn't choose
hiding in the sleeve of his jacket,
so that the participant is now asked to explain
why they chose the car that, in fact, is not the one they chose at all,
but the other one.
The interesting point is that actually most people don't even notice
that the cars have been changed.
(Laughter)
This is because all cars look the same, even the ones outside today.
But moreover, the people in this experiment were very, very happy
to give lots of reasons why they had chosen the car
which in fact was not the car they chose at all.
They talked about the color or the shape and why they liked it.
But really, that was just a confabulation.
They were retrospectively inventing an experience of their own decision,
which was clearly not what their brain had originally done.
So we can't trust the way we think about our own decisions.
The second point I'd like to make about the bridge between decision and action
is that in our culture, we think we're free,
we think that we freely decide,
that somehow, there's an "I" somewhere in my brain
which is making the decisions,
and it's because I decide freely what I do that I can control my actions,
influence the world around me and become responsible.
But that's not quite right either,
and I'm going to show you a simple experiment we've done recently,
which looks at this relation between free decision
and the sense of control and responsibility.
Very simple experiment.
You see a left-pointing arrow on the screen
and you press the button with your left hand.
Sometimes you see a right-pointing arrow on the screen
and you press the other button with your right hand.
Really simple.
This is the interesting bit: sometimes, you see a double arrow.
It's up to you what you press.
You're free, it could be left or right, it's completely up to you.
The person might press right or they might press left,
but the interesting point is that before the double-headed arrow,
we flash up, very, very briefly, this little black arrow on the screen,
which can either point to the right, as here,
or in other cases, it can point to the left,
and we call that the subliminal prime.
It's only there for 16 milliseconds, and that's so quick that you don't see it.
You can't see that arrow at all,
but your brain can nevertheless take in the information.
Because if you look at what people do
after they've been shown a subliminal prime pointing to the right,
it turns out they're a little bit more likely
to "freely choose" to use their right hand than their left.
So it's not really that free at all, is it?
It's actually the prime that's controlling them.
It's not a total effect, it's not 100% certain,
but they're more likely to choose right after a right prime
and more likely to choose left after a left prime.
So I think we can see that now.
In this particular case, the person's going to choose right.
So, what this means is we can influence people's behavior
by information that they're not even conscious of.
They don't see those primes at all.
But we were interested in the feeling that we actually control their actions
and that we're responsible for what we do,
because that's the basis of our society.
So, we made this experiment a little more interesting,
because every time you pressed the button, a color flashed up on the screen.
And the critical point is that, here, we've got a right-pointing prime,
a double-headed arrow -
You choose to go right,
and we're going to present the color green.
In other trials, you might have a right-pointing prime,
but you might resist the prime somehow and choose to go left,
and then you'll get a different color; in this case, you'll get the color blue.
So there's a whole set of colors flashing up on the screen.
And we're interested in how people understand their control
over the colors that they're causing.
So we're going to ask them after every color,
"How much control did you think you had over the color that came on the screen?
And they just give a judgment in percent between "Zero - nothing to do with me"
and "100% - it's great, I'm in control."
Now, what we're interested in is: what do these subliminal primes,
which you don't even see, but which influence your free choice,
do to your feeling of responsibility and control over what happens?
So here what you have is the situation on the right of the screen,
where the person is resisting the prime.
So we might prime them to the right, they get the double-headed arrow,
but for some reason decide to press with the left-hand button
and they get a particular color. in this case, blue.
And they'll say, "Well, about 55% control."
But now, let's compare that
to the case where we subliminally influence their free choice
and we push them to decide the way we want.
So now we're going to prime them to the right
and they might actually choose in this case to press with their right hand
in response to the double-headed arrow, and they get a different color.
And in this case, they give a higher rating of control.
The difference between these two numbers looks numerically small,
but it's highly reliable, statistically.
So, the interesting point here
is that although the person never sees the prime that influences their behavior,
they think they're more in control of what they're doing,
even though they're actually less in control.
So the concept that the participants are forming,
that they're controlling the colors on the screen,
is really a little bit of an illusion.
The point where they feel most in control of the consequences of their actions
is in fact the point where we, as the experimenters,
are controlling them most.
So, "don't necessarily trust the feeling that you're in control of your life"
might be the message from those experiments.
Now, if we look at the human brain,
we can do now with MRI decision-making experiments
and experiments where people decide which of several actions to make,
in a brain scanner.
And I just want to give you a very quick flavor of the way these data work.
You don't find a single decision center.
You don't find a single sort of "I" or homunculus in the brain.
You don't even find separate decision centers
for food and clothes and investments, no.
It doesn't seem as though there are separate decision centers like that.
Rather, you find separate areas
which are concerned with different aspects or different dimensions of the decision.
So here, in green, you have an area in the frontal part of the brain
which is concerned with what we call "what" decisions,
deciding between two alternative actions which have equal value.
So, for example, in the experiments that I showed you,
the very simple choice of whether to press with your left hand or your right hand
involves that particular area.
But if I tell you exactly what you have to do,
but then leave it up to you when you do it,
then you find a different area, which is the area shown here in red,
which is deciding when to make a particular action.
Now, this is really crucial because you all know
that there are lots of actions which are appropriate in one situation,
but totally inappropriate in another.
So knowing when to make the action, even after you've decided to make it,
is often essential.
And I just want to leave you with one little final thought,
which we call the "whether decision."
Sometimes, it's extremely important
to have the capacity to develop a plan of action
to get almost to the point of acting and then stop,
like the goalie, staying in the middle, which sometimes works.
Most of us have had the experience of writing an email -
an angry email to our boss is a quite common one,
"Why did I not get a pay rise?"
You're about to click the "Send" button and you hear a little voice saying,
"Patrick, do you really want to send that?"
(Laughter)
And the answer is, "No, don't send it."
Now, there is no little voice in the head,
but what there is is the capacity to hold back an action at the last moment.
There's a point of no return.
And the area that's shown in blue there,
it seems to be the area
which makes the final decision whether to commit to action or not.
So it's the gatekeeper of self-control.
And for social animals like humans,
who are very, very flexible in what they can do,
in what actions they can make,
but whose actions have wide social impact on other people,
this ability to simulate an action and say, "Do I really want to do that?"
and then possibly hold back,
is absolutely fundamental,
and I think that's one of the reasons why we're able to sustain in our society
ideas like legal responsibility for what we do.
It's because the brain offers us the capacity to hold back
when it becomes inappropriate.
Thanks very much.
(Applause)