We have historical records that allow us
to know how the ancient Greeks dressed,

how they lived,

how they fought.

But how did they think?

One natural idea is that the deepest
aspects of human thought,

out ability to imagine,

to be concious,

to dream,

have always been the same.

Another possibility

is that the social transformations
that have shaped our culture

make us also change the structural
columns of human thought.

We may all have different
opinions about this.

Actually, it's a longstanding
philosophical debate.

But is this question
even amenable to science?

Here I'd like to propose that in the same way

that in the same way
that we can reconstruct

how the ancient Greek cities looked like,

just based on a few bricks,

that the writings of a culture
are the archealogical records --

the fossils --

of human thought.

And in fact,

doing some form of psychological analysis

of some of the most ancient
books of human culture,

Julian James came in the '70s
with a very wild and radical hypothesis,

that only 3,000 years ago,

humans were today
what we'd call, schizophrenics.

And he made this claim

based on the fact that the first humans
writing these books behaved consistently

in different traditions and in different
places of the world,

as if they were hearing and obeying voices

that they perceived
as coming from the Gods,

or from the muses.

What today we'd call hallucinations.

And only then,

as time went on,

they began to recognize
that they were the creators --

the owners of these inner voices.

And with this they gained introspection:

the ability to think
about their own thoughts.

So Jaynes' theory is that conciousness,

at least in the way we perceive it today,

where we feel that we are the pilots
of our own existence,

is a quite recent cultural development.

And this theory is quite spectacular,

because an obvious problem,

which is that it's built on just a few
and very specific examples.

So the question is

whether the theory that introspection
built up only about 3,000 years ago,

can be examined in a quantitative
and objective way.

And the problem on how
to go about this is quite obvious.

It's not like Plato woke up one day

and then he wrote,

"Hello, I'm Plato

and as of today I have a fully
introspective consciousness."

(Laughter)

And this still is actually
what is the essence of the problem.

We need to find the emergence
of a concept that's never said.

The word introspection
does not appear a single time

in the books we want to analyze.

So our way to solve this
is to build the space of words.

This is a huge space
that contains all words

in such a way that they distance
between any two of them

is indicative of how
closely related they are.

So for instance,

you want the words dog and cat
to be very close together,

but the words grapefruit and logarithm
to be very far away.

And this has to be true for any
two words within the space.

And there are different ways that we
can construct the space of words.

One is just asking the experts,

a bit like we do with dictionaries.

Another possibility

is following the simple assumption

that when two words are related
they tend to appear in the same sentences,

in the same paragraphs,

in the same documents,

more often than would be expected
just by pure chance.

And this simple hypothesis,

this simple method,

with some computational tricks

that have to do with the fact

that this is a very complex
and highly dimensional space,

turns out to be quite effective.

And just to give you a flavor
of how well this works,

this is the result we get when
we analyze this for some familiar words.

And you can see first

that words automatically organize
into semantic neighborhoods.

So you get the fruits,

the body parts,

the computer parts,

the scientific terms

and so on.

The algorithm also identifies
the reorganized concepts in a hierarchy.

So for instance,

you can see that the scientific terms
break down into two subcategories

of the astronomic and the physic terms.

And then their are very fine things.

For instance,

the word astronomy,

which seems a bit bizarre where it is,

is actually exactly where it should be,

between what it is --

an actual science --

and between what it describes --

the astronomical terms.

And we could go on and on with this.

Actually if you stare at this for awhile

and you just build random trajectories,

you will see that is feels well --

actually it feels a bit like doing poetry.

And this is because in way,

walking in this space
is like walking in the mind.

And last thing is that this algorithm
also identifies what are our intuitions,

of which words should lead
in the neighborhood of introspection.

So for instance,

words such as Self, Guilt,
Reason, Emotion,

are very close to introspection,

but other words,

such as Red, Football, Candle, Banana,

are just very far away.

And so once we've built this space,

the question of the history
of introspection,

or of the history of any concept,

which before could seem abstract
and somehow vague,

becomes concrete --

becomes amenable to quantitative science.

All that we have to do is take the books,

we digitize them

and we take this stream
of words as a trajectory

and project them into this space,

and then we ask whether this trajectory
spends significant time

circling closely to the concept
of introspection.

And with this,

we can analyze
the history of introspection

in the ancient Greek tradition,

for which we have the best
available written record.

So what we did is we took all the books --

we just ordered them by time --

for each book we take the words

and we project them to the space,

and then we ask for each word
how close it is to introspection,

and we just average that.

And then we understand
that as time goes on and on,

these books get closer,
and closer and closer

to the concept of introspection.

And this is exactly what happens
in the ancient Greek tradition.

So you can see that for the oldest books
in the Homeric tradition,

there is a small increase with books
getting closer to introspection,

but about four centuries before Christ,

this starts ramping up very rapidly

to an almost five-fold increase

of books getting closer,
and closer and closer

to the concept of introspection.

And one of the nice things about this

is that now we can ask

whether this is also true
in a different independent tradition.

So we just ran this same analysis
on the Judeo Christian tradition,

and we got virtually the same pattern.

Again you see a small increase
for the oldest books in the old testament,

and then it increases much more rapidly

in the new books of the new testament,

and then we get the peak of introspection

in the work Confessions
of Saint Augustine,

about four centuries after Christ.

And this was very important,

because Saint Augustine
had been recognized

by scholars, philologists, historians,

as one of the founders of introspection.

Actually, some believe him to be
the father of modern psychology.

So our algorithm --

which has the virtue
of being quantitative,

of being objective,

and of course of being extremely fast,

it just runs in a fraction of a second --

can capture some of the most
important conclusions

of this long tradition of investigation.

And this is in a way,
one of the beauties of science,

which is that now this idea can translated

and generalized to a whole
lot of different domains.

So in the same way that we asked
about the past of human conciousness,

maybe the most challenging question
we can pose to ourselves,

is whether this can tell us something
about the future of our unconciousness.

To put it more precisely,

whether the words we say today

can tell us something of where
our minds will be in a few days,

in a few months,

or a few years from now.

And in the way many of us
are now wearing censors

that detect our heart rate,

our respiration,

our genes,

on the hopes that this may
help us prevent diseases,

we can ask whether monitoring
and analyzing the words we speak --

we tweet,

we email,

we write --

can tell us ahead of time whether
something will go wrong with our minds.

And with Guillermo Cecci,

who has been my brother
in this adventure,

we took on this task.

And we did so by analyzing the recorded
speech for 44 young people

who were at a high risk
of developing schizophenia.

And so what we did is we
measured speech at day one

and then we asked

whether the properties
of the speech could predict --

within a window of almost three years --

the future development of psychosis.

But despite our hopes,

we got failure after failure.

There was just not enough
information in semantics

to predict the future
organization of the mind.

It was good enough

to distinguish between a group
of schizophrenics and a control group,

a bit like we had done
for the ancient texts,

but not to predict the future
onto the psychosis.

But then we realized

that maybe the most important thing
was not so much what they were saying

but how they were saying it.

More specifically,

it was not in which semantic
neighborhoods the words were,

but how far and fast they jumped
from one semantic neighborhood to another.

And so we came up with this measure,

which we termed Semantic Coherence,

which essentially measures

the persistence of speech
within one semantic topic,

within one semantic category.

And it turned out to be

that for this group of 44 people,

the algorithm based on semantic cohernece

could predict with 100 percent accuracy

who developed psychosis and who will not.

And this was something
that could not be achieved --

not even close --

with all the other
existing clinical measures.

And I remember vividly
while I was working on this,

I was sitting on my computer

and I saw a bunch of tweets by Polo.

Polo has been my first student
back in Buenos Aires

and at the time he was living in New York.

And there was something in this tweet --

I could not tell exactly what
because nothing was said explicitly --

but I got this strong hunch,

this strong intuition
that something was going wrong.

So I picked up the phone
and I called Polo,

and he was not feeling well.

And this simple fact that reading
in between the lines

I could sense through words
his feelings,

was a simple but very
effective way to help.

What I tell you today

is that we're getting
close to understanding

how we can convert this intuition
that we all have,

that we all share,

into an algorithm.

And in doing so,

we may be seeing in the future
a very different form of mental health,

based on objective, quantitative
and automated analysis

of the words we write,

of the words we say.

Gracias.

(Applause)