David Chalmers: Okay! Welcome everyone to our debate on "Do split-brain patients have two minds?"
This is the latest in a series of
debates organized by the Center for Mind,
Brain, and Consciousness on foundational
issues in the mind brain sciences. I'm
David Chalmers co-director of the Center
along with Ned Block.
Possibly--I mean, the split-brain phenomenon is one of the most serious challenges to our
traditional ideas of consciousness and
the self that comes from modern
neuroscience. I mean, it's a traditional
thesis in philosophy that consciousness
is essentially unified; that the self is
indivisible; that a human being goes
along with one--is attached somehow to
one single indivisible mind.
But the split-brain phenomenon at least
threatens to cast doubt on all of this.
I mean, thinking about the two
hemispheres of the brain and its
connection to the mind goes back quite a
long way. Maybe if you want to come
around there there's a bit of spare room.
Back in the 19th century there
were some thinkers who noted the duality
of the brain, the two hemispheres, and
went on to argue that even normal
subjects with normal brains somehow have
two minds. To which the common response 
was, well no, they're unified, because
there's communication between the two
hemispheres of the brain via the corpus callosum--
the fibers that connect the two
 hemispheres of the brain.
But in in the 20th century people began 
to perform operations that would sever
the corpus callosum, and thereby separate
the two hemispheres of the brain to a
much greater extent. I think the first--
the history of all this is recounted
really beautifully by Elizabeth Schechter 
in her book on the split-brain
phenomenon, starting from the
19th century and onwards. It seems that
the the first of these experiments were
done around 1940 to treat epilepsy
patients with seizures. It seemed that
these seizures could be reduced by
dividing the hemispheres. At first these
operations were somewhat partial but
then later on, in the 60s and 70s, there
were more drastic split brain operations
that involved different degrees, but a
more complete severance of the
connection between the hemispheres. And
first after the neurosurgeons perform
these operations then the psychologists
and neuroscientists got involved
studying these patients. And although in
many circumstances it seems these
patients would behave in fairly normal
ways there were at least some
experimental context where behavior was
produced that was to many people
somehow reminiscent or suggestive of the
idea that each hemisphere might be
associated with a mind of its own. I mean
there's the phenomenon by which--it was very
hard to get--if you asked them what--if you
asked them, for example, to compare what's
presented in the left half of the visual
field and the right half of the visual
field, many patients found these
comparisons very difficult, even though
they might have no problem identifying
what's in the left half or what's in the
right half. More drastically, it would seem
that at least in some situations you
could ask someone--a patient could report
what's present in say the right half of
their visual field, but they couldn't
report what's in the left half of the
visual field, because the right half of
the visual field goes to the left
hemisphere which controls speech. The
left half of the visual field goes to
the right hemisphere which. on the
standard view, doesn't control speech, so
they couldn't report it.
Nonetheless if you ask them to to reach
out with their left hand, and maybe draw
what they're seeing. They could
draw it. So to many people this was
somehow suggestive that there was two
separate spheres of consciousness: one
associated with the left brain, and one
with the right brain. I mean--and
then that led to a very lengthy set of
arguments among neuroscientists,
psychologists, and philosophers. I mean,
Roger Sperry got the got the Nobel Prize
in part for his work on these patients.
Philosophers like Tom Nagel wrote
classic analyses of these phenomena back
in the 1970s, and there was an argument
from way back then for people saying
there are two minds associated with the
two hemispheres; some saying there's just
one mind associated with both. The
view was out there that maybe there was a
there was a consciousness associated
with the the left hemisphere because
that controls speech. And there indeed
are the views where maybe there's no
binary fact of the matter about how many
minds there are. Recently--so that was the
debate back in the the 1970s--recently,
this debate has been revisited for a
couple of reasons. Within philosophy,
Elizabeth Schechter has just written a
very important book on the split-brain
phenomena, called Self-Consciousness and
"Split" Brains: The Minds' I,-in
which she gives a really thorough
recounting and analysis of the phenomena,
and argues based on the evidence about
these patients that in fact they're
best regarded as having two minds.
Lizzie has a view where there's somehow a
single subject, but--that has two minds.
Hence the subtitle of the book "The Minds'
I" where the apostrophe comes after the 's'.
The two Minds have a
single I, and that's provided
a real boost for the two minds
 view. At the same time,
Yair Pinto, whose training's in
psychology, is working in a brain and
cognition lab in Amsterdam--has
provided some new empirical studies of
some of these patients. He's come across some patients who had their--this operation performed
a number of decades ago, 
and has been doing
experiments on them, which he has
interpreted, suggest that the evidence
for the two minds view is not as strong
as some people have thought, and is
perhaps more consistent with the single
mind view. So there we have an advocate
of the the two minds view and an advocate
of the single mind view. However, this
debate is not your ordinary,
old-fashioned, two-way debate--that would
be--that seems kind of inappropriate for
this--for this debate, where we're arguing
about whether, you know, binary analyses
of these phenomena are the right kinds--
are the right approach at all. We thought
it's appropriate to have an intermediate--
an intermediate view. So our own local
hero, Joe LeDoux, who did very important
work on this back in the 1970s,
has a classic paper on the split-brain
phenomena from 1977, is going to give us
his perspective, which involves a view
which is in certain respects
intermediate between the 'single mind' view
and the two mind view, or it may, for example,
depend on context. So that's the set up
for our debate today.
We'll have professor 
Elizabeth Schechter from
Washington University will speak for 15
minutes in defense of the two minds view.
We'll have Dr. Yair Pinto
from University of Amsterdam will speak
for 15 minutes and defense of the one
mind view. We'll have Professor Joseph
LeDoux from NYU will speak in defense
of his
intermediate view for 15 minutes. Then
each of our speakers will then have a
chance to respond to the previous
speakers, five minutes each. Then we'll
all come up for discussion. So 15
15 15, 5 5 5, followed by hopefully a
healthy chance for Q&A to get the
audience involved. Okay, so enough said. Will
you please join me in welcoming our
first speaker, Lizzy Schechter from
Washington University.
[Audience Applauds]
Elizabeth Schechter: Thank you very
much. It's an honor to be here today. I'm
not that microphone-experienced, so, you
know, signal to me somehow if I step out
of range. I'm very fortunate that
Dave gave such a great introduction
to the split-brain phenomenon. I could
move especially quickly through my own
introductory remarks. "Split" brain surgery
is a colloquial term for a surgery
cutting through the corpus callosum and
sometimes additional white matter tracts
connecting the two cerebral hemispheres.
While these surgeries were performed on
human beings for strictly medical
reasons, unsurprisingly they have some
psychobehavioral consequences, and the
collection of these consequences became
known as the split-brain phenomenon. In
brief, after they're surgically separated
from each other in this way at the
cortical level, the two hemispheres of
the brain begin to operate independently
of each other--not wholly but to an
unusual degree, in the realm of
perception cognition and the control of
action. And this emerges most clearly
under the conditions of the split-brain
experiments. So, split brain experiments
have two paradigmatic design features
that are used either singly or together.
And I call them stimulus lateralization
and response lateralization. Stimulus
lateralization means that perceptual
information is carefully directed to
only a single hemisphere at a time--to
the extent possible. So, in the case of
vision, for instance, the easiest way to
do this would be to have a split-brain
subjects stare at a particular point on
a screen. Everything--as long as they keep
their gaze fixated there--everything
presented to the right of this point
would be received directly by the left
hemisphere. Everything presented to the
left of this point would be received
directly by the right hemisphere.
Response lateralization, meanwhile, means
that split-brain subjects are asked to
respond to this perceptual information
using a form of motor behavior that is
believed to be at least predominantly
under the control of one hemisphere or
the other. So, right hand behavior
predominantly controlled by the left
hemisphere, left hand behavior by the
right hemisphere, and speech, most often,
predominantly or exclusively, under
control of the left hemisphere. And again
what we're here to debate
today is whether split-brain surgery
divides split-brain psychology in such a
way, or so substantially, that after the
surgery the two hemispheres of the brain
are in fact associated with distinct
minds. And, as you heard, my position in
this debate--I've been brought in to
represent the two minds position, which
is one of the major theses defended in
my recent book. And what I want to do
first is talk about a respect in which
this thesis--my version of this thesis--is
very radical, and a respect in which it is
more modest. So the radical aspect is
that when I say that a particular 
split-brain subject has two minds, I actually
mean that that subject is not a unitary
psychological being, but is actually
composed of two distinct psychological
beings. So that, of such a subject, we can say
that it is not this subject as a whole, S,
that thinks and feels and decides and
sees and points and speaks and so on, but
rather that there are two psychological
beings within the split-brain subject
who do each of these things. And I use
the letters R and L to refer to these two
psychological beings. I'll refer to them
as distinct hemisphere systems, although
it might be relevant to know that
I don't take them to be mere hemispheres.
So my own view is that a mere
hemisphere doesn't think or speak or
point. Rather, they're hemisphere -associated systems.
I believe that each of these systems 
is almost the entire animal.
It's just that neither of them includes 
both hemispheres at once.
The modest aspect of the claim--and I don't know if
this will come up today--but in the book
I suggest that the claim is true of some
split-brain subjects but not actually
true of all split-brain subjects. And
what makes this possible is that from my
perspective what grounds
the two thinkers claim--again, the claim that
there are two distinct psychological
beings composing a split-brain subject--
what grounds this claim are facts about
interhemispheric psychological, i.e. mental
state, interaction. And interhemispheric
interaction differs across split-brain
subjects, and to some extent it differs
even within subjects across time.
Okay, so the first point I want to address is just
how is this even possible? How is it
possible for there to be two distinct
thinkers within one animal, one human
being. Ordinarily, we just assume that if
there's a thinking thing here, it's
obviously the animal. The answer is that
a psychological account of the
identities of thinkers will be at least
substantially a causal or a functional
account. So it will be an account according
to which thinkers are thinking systems;
systems within which thinking goes on.
I'm using thinking as an umbrella term
here to refer to all manner of familiar
psychological activities, so I'm using
thinking to refer to not just thinking
but seeing and feeling and
decision-making and 
intentional acting and so on.
So taking thinking to be an umbrella
term here, thinking itself will be
causally or functionally defined. It's
going to consist in a collection of
specific kinds of causal activities. And
split-brain surgery changes the way
these causal activities operate in the
brain, such that--again at least in these
subjects of whom the claim is true--these
activities operate, continue to operate--
these activities that are constitutive
of thinking--continue to operate within
each hemisphere system but not or not as
much across them. So obviously these
introductory remarks are supposed to be
brief but just to give you a quick
outline of the argument for this claim,
the two thinkers claim: the first idea we
need is that what makes mental states
and activities of the particular
psychological type that they are--so, for
instance, what makes something an
instance of consciously perceiving as
opposed to non-consciously perceiving
something--is very largely the other--the
ways that this activity can interact
with other mental activities, but
implicitly only other mental activities
of the same mind. And this is something
that the philosopher Sidney Shoemaker--
it's an idea that he articulated and
defended in his materialist account of
personal identity sometime ago. So, just
to give a toy example here,
and it's Shoemakers example--you'll often
read something like--in philosophical
literature you might read something
that says, "well, beliefs and desires are
such that a belief that--to use his example,
and it's very relevant today--the belief
that it's raining combines, interacts
with, a desire to stay dry, to produce
taking an umbrella. And when you read
something like this, this is
supposed to be a characterization of the
essential causal nature of beliefs and
desires. It often is expressed in the way
I just put it, such that a belief that
it's raining interacts with a desire to
stay dry to produce taking an umbrella.
But of course implicitly we mean a
belief that it's raining interacts with
a co-mental desire, a desire of the
same mind, to produce taking an umbrella.
So, for instance, if it's just, you know, if
I'm the one who believes that it's
raining but I don't care whether I get
wet, you're the one who really wants to
stay dry but you have no idea that it's
raining, then presumably neither one of
us will take an umbrella. So, again, it's
always with other mental states and
activities of the same mind that
particular mental states and activities
have their sort of their characteristic
or essential causal profile.
Now the empirical aspect of the two thinkers
claim for split-brain subjects is the
claim that after split brain surgery,
mental states and activities continue to
interact in these type-defining ways, but
only relative to, only with, or at
least predominantly with, other mental
states and activities of the same
hemisphere system. So, what this means is
that they retain their psychological
identities only relative to, again, one
hemisphere system or the other.
Normally, for instance, if we go back to
the umbrella case, you would say "okay, so
if this animal believes that it's
raining and this animal wants to stay
dry then this animal will take an
umbrella." But in the split-brain case
what emerges under experimental
conditions is that we see that actually
what we need to say is that the belief
of this hemisphere system that it was
raining interacts with a desire of this
hemisphere system in order to produce
taking an umbrella. So, what this means is
that it places these hemisphere systems,
R and L, rather than the animal as a whole, in
this thinking role that is usually
occupied or played by whole animals. Okay,
so let me give an example here of an
experiment I really like. So, imagine that
in this experiment you have a split-brain
subject who is looking at a screen--
and I don't know how well this shows up
here but we can treat this as the
stimulus-- so, there's a little minus sign
between the words 'scraper' and 'sky' up here.
So we can treat this minus sign as the
central fixation point. And given that
one word is presented on either side of
the central fixation point these stimuli
are thus lateralized to distinct
hemispheres. So we have the word 'sky' in
the right visual hemifield, that should
be received by the left hemisphere. We have
the word 'scraper' in the left visual
hemifield, that should be received by the
right hemisphere. And the question--and
then the split-brain subject is given
a pencil and a sheet of paper. and
is just asked to draw what they saw,
or the referent of what they just saw.
And the question is what they're going
to draw. So what the experimenters found
is that quite often a split brain
subject would in fact draw the reference
of each of these words--I don't know if
you can see this but this is an ice
scraper under a partly cloudy sky--but
would not draw the single referent of
the compound word that 'sky' and 'scraper'
can be combined to form. Thank you.
So it's as if in this case someone saw the
word 'sky', and drew a sky, someone saw the
word 'scraper' and drew a scraper, and no one
saw 'sky-scraper'. In contrast, when you
have, similarly two, words that aren't
closely semantically related, but that
can be combined to form a single
compound word, and these are both
presented in the same visual hemifield, 
at least in this case in the right
visual hemifield, what you see is that
the split-brain subject--here the words are
moon and honey--but the subject doesn't
draw a pot of sweetener underneath a
celestial object, but instead draws a
loving couple, the single referent
of the compound word. So in this case
it's not only as if someone saw the word
'moon' and someone saw the word 'honey', but
someone saw the words 'honeymoon' and put
them together. And, in fact, that's what I
argued; that's the position.
What's interesting about this experiment
is that, in fact, the subject was drawing
with a single hand on all these trials,
so the subject is just given the pencil
to hold in a single hand and is asked to
draw what they saw. And in cases in which
the two words were semantically related,
you've sometimes got a drawing that
looks as though it's the product of a
single mind or a single agency, right?
So, with bow and arrow, presumably this is no
different from what a non-split subject
would draw in this case, right? We have an
arrow leaned across a bow. But what we
see from the skyscraper case is that the
impression that this drawing is being
produced by a single thinker that saw
both words is actually misleading.
Instead, what you have is the two
hemisphere systems taking turns
controlling the drawing hand. So, I think
this is an important result because what
you often hear about the split-brain
phenomenon is that the reason the
experimental results evoke the 
intuition--right or wrong--that a split-brain
subject has two minds is that the
subjects behave in a strikingly
disunified fashion under these experimental
conditions. But there's nothing
necessarily strikingly disunified about
even the skyscraper case, much less the
bow-and-arrow case. So, I think that this
isn't the right answer.
It's rather, in my view, because it
doesn't seem to be the product of the
kind of integration that characterized
the workings of a single mind. How much
time at this point? Okay, great. Okay, so
I'm gonna explain another example here
to illustrate this and it's subtle but I
think, again, it's important. So, this
experiment compared the behavior of
split-brain to non-split subjects with
bi-manual drawing. So, imagine you're
given a sheet of paper and now a pencil
to hold in each hand. And you're asked to
draw two different things simultaneously.
This is something non-split subjects
find very difficult unless they're
drawing something that's symmetric in
the right kind of way. And imagine that
what you're supposed to draw with each
hand is a semicircle or an arc, and one
of the arcs, its open end is going to
point up; one of the arcs, its open end
is going to point down. You have to
produce these drawings one above the
other. And what varies between trials is
whether the arc whose open end is pointing
up is above or below the other one. So, in
other words, what you're asked to produce
is either something that looks like the
drawing on the left on some trials or
something that looks like the drawing on
the right on other trials. I don't know
if you have a sense of--you can close
your eyes and try to do it right now--
which of these would be harder for you
to produce. But if you look at non-split
subjects, they find it
significantly easier to produce the
drawing on the left. Why is this? I'll
note again that of course non-split
subjects find it difficult to draw with
both hands simultaneously. But the one on
the left is much easier. Presumably, the
reason why--because nothing else differs
between the tasks--is that in the case on
the left the subjects can conceptualize
the hands as working together to create
a single task to draw a circle, because
this is a familiar kind of object.
Whereas in
the case on the right, they can't. And,
in fact, that's what some of the subjects
said: that they were able to think of
themselves as drawing a circle just
using both hands in the former case and
somehow conceptualizing--being able to
conceptualize these two uni-manual
tasks as, in fact, aspects of a single
bi-manual task, mitigated whatever
perceptual and motor constraints there
are that make bi-manual drawing
difficult for non-split subjects. For
split-brain subjects, on the other hand,
the tasks are of equal ease. Non-split
subjects are actually better at bi-manual
drawing. So, again, the reason for this,
from the perspective I'm defending, the
reason--[clears throat] excuse me--the reason for
this difference is that a non-split
subject is one thinker who is struggling
to do two things at once. And, again, it's
helpful for the non-split subject to be
able to think of both hands as
contributing to a common task. Whereas a
split-brain subject is two agents, each
of whom is using a hand to perform a
task. And it makes no difference to
either of these thinkers what the other one
is doing. Thank you.
[Audience applauds]
Dave: Okay! Thanks very much, Lizzie! Our second
speaker, defending the one mind view, will
be Yair Pinto from the University of
Amsterdam.
[Audience applauds]
Yair Pinto: Alright. Yes, indeed, thank you
very much for having me, or inviting me
for this debate. And thanks Lizzy for the
really good introduction. So I'll just go
through this quickly. I'm going to
indeed defend that there's only one mind in
a split-brain. And what do I mean by that?
With a split mind, I mean that, as
Lizzie also said, that there's two people
in one hat. So there's two independent
conscious agents--one per
hemisphere. And I think that this is not
the correct view, and I'll start with an
allegory. Imagine--and I'll explain later
what is relevant--imagine that
somebody goes to the doctor and he has a
flu or something. And the doctor says,
"well, yeah, yeah, you indeed have a flu, but
I also have very bad news: you're
actually blind. And then the patient
responds, "no, no, I'm really not blind. I
mean, believe me, I have visual
experiences right now. I'm not blind." Well,
you could say well this is still
possible, you know. You have Anton's
syndrome and stuff. But imagine all the
people he knows really well, the closest
ones to him, also say to the doctor, "no, no,
believe me, doctor, this guy is not blind."
Okay. It's still logically possible that
this guy is indeed blind. But the
point here is, it's an extraordinary claim and
you need really solid evidence for this.
Okay. So what does this all have to do
with split-brain? I would say split-
consciousness is almost a non-starter, because
what happens if you work with split-
brain patients--it's also mentioned in
literature very often and I myself
worked a lot with these patients--if you
ask them how do you feel they say, "The
same as before the operation. I'm just
one person." So it's basically the
scientists telling them, "no, but you're
actually two people." So the split-brain
says, "no, no, wait, wait, that cannot
be right. I'm actually just one person.
I'm not two people."
And more--even more surprising maybe,
or even more challenging for the two
persons view, the closest people to
the split-brainer also say, "no, he's really
just one person. He's really just the
same as he was before the operation." And
before I go on to--in some more depth
into this, think about what this means:
think about that we would do a split-
brain operation on you. So, right now you
see your entire visual fields, you
sense your entire body, and you control
your entire body. Now we cut your corpus
callosum, and now you're just your left
hemisphere. So what does it mean if
you're just your left hemisphere? It
means you only see things to the rights
and in your in your right visual fields;
you only sense the right side of your
body; and you only control the right side
of your body. And it's somebody else
controlling the other side of your body.
So, in a way it's weird: how could you not
notice this? You went from completely
sighted to half-blind and half-paralyzed.
And even more surprising maybe: the
people that are closest to you don't
notice this either. You still come across--although you now share your body with
somebody else--somehow you manage to work
together so closely, even though you're
not aware of each other's presence, that
people close to you do not notice there
are actually two people now [inaudible].
Okay, so it is logically possible, but it
needs strong proof. Okay, so what is not
compelling evidence. So if you look at
actual split-brain literature,
most of the papers are actually on a
hemispheric specialization. So what does
hemispheric specialization mean? You
present something in the left visual
fields, which projects to your right
hemisphere, and they're better in certain
stuff. And when you present something to
the right visual fields, they're better
in other stuff. Which suggests that each
hemisphere has its own strengths. So, for
instance, when you present words to
the split-brain patients, he's better at
recognizing words when they're presented
to the right visual field, and he's better
in recognizing images when they're
presented to the left visual field.
However, I don't think this is strong
proof that there's two people in there,
because you also find hemispheric
specialization in normal people with a
unified mind. So if we do the same
experiment--these experiments have
been done often--if you flash a word for 150
milliseconds, people are better at
recognizing this word when it appears
in the right visual fields, and they're
better at recognizing images when
they're presented to the level fields. So
this cannot be proved for split-minds
because it also happens in normal
people with a unified mind. Another
important data point is that--or another
important argument is put forwards: well
they split attention. Each hemisphere
scans half the visual field
independently of the other. But there are
cases where we also have paid attention.
So that cannot be a valid argument either.
Okay, so we've been doing a lot of
talking here. So now a short Intermezzo,
where I want you to participate. I'll get
this to work. So this is a multiple object
tracking task. At the beginning you'll
see four dots flashing. Track them with
your attention.
Yeah, well, that's basically it. If it
works, I hope.
Yeah, here we go.
Alright, how did you do? Yeah? I see a lot of
people nodding, so it went well, I guess.
Okay, so why did I show this? Actually,
when you did this just now, you had split
attention. So we noticed from studies
where you present the stimuli
bilaterally or unilaterally, your
capacity is double when we present these
stimuli bilaterally. So it seems that
each hemisphere is tracking
independently of the other. And even more
in EEG studies, when an item crosses the
mid-line during MOT, or during multiple
object tracking, you see in the CDA of
the EEG signal--you see that item is
transferred from one hemisphere, the
information about the item is transferred
from one hemisphere to the other. So you just
experienced split attention. But you were
still one person, clearly. Okay, so what is
compelling evidence--and this is from a
review in nature in 2012, and you find
this basically in every textbook for a
good reason, because this is very strong
evidence, and I think David already
mentioned this, that there are really two
people in one hat there. And what do
we see here? Here we see the word 'face'.
It's presented in the right visual
fields, which was actually the left
hemisphere, which controls language.
Nothing special happens--the person just
says, "oh, yeah, I saw the word 'face'." However,
the interesting thing happens when the
word 'face' is presented to the left
fields. Now the patient says, "I saw
nothing," yet he draws the face with his
left hand. And then you ask him, "oh, you
just said you saw nothing. Why do you draw it with your left hand?"
He's like, "I don't know." Okay, so this,
of course, is a very classical finding in
split-brain literature, for a good
reason: because you never--this never
happens in normal people with a unified
mind. And it really--it's basically an
implication of the split-mind idea: if
there are really two people there, one in
the left hemisphere, one in the right
hemisphere, yeah this makes sense. The
person in the left hemisphere does not
see the word 'face' and the person--left
hemisphere controls language, so this
person says, "I saw nothing." Yet, the person
in the right hemisphere controls the left hand,
and he did see the word, and he indicated it
by drawing with the left hand, which he
controls. Okay, so why am I not convinced
of the two minds view? There's one big
problem with this data points. So you can
find this data point in articles from
the 60s--from Gazzaniga and Sperry.
But it's always described in a very
qualitative way, basically as an anecdote.
So there's no data there, there's no
quantitative data, which says like, "how
many trials did we do, how often did this
occur," and so on. And there's a big
problem with anecd--I mean you all can
also see examples of this on YouTube,
where you see patients [inaudible] doing
these kind of things. There's a big
problem with anecdotal data. Yeah, it's
very appealing, but it can also be
misleading. For instance, if we would take
anecdotes of people having predictive
dreams, we would all be convinced, "yeah
people can really predict the future in
their dreams, you know. My cousin he dreamt
something, and two days later, really
happens!" And I made a video on that in my
iPhone, I put it on YouTube, and if you
see, you're like, "yeah, he can really
predict [inaudible]." But if we don't have
quantitative data, we don't know how
representative it is. And that's why we
did a study, which David already
mentioned. So what it is--and we published
this last year--so I'll talk you through
the setup of the study. We just wanted to
quantify how solid is this data point
basically, how much does it really occur.
So stimuli were presented anywhere in the
visual field, either in the left or the
right visual fields, or no stimulus was
presented at all. And it asked--the
participant was to indicates whether
there was a stimulus, and if so where. The
crucial thing--of course, stimulus
conditions were intermixed, so the
patient did not know beforehand whether
there was stimulus, and if so, if there
was stimulus, where it would appear. The
important thing was that response type
was blocked. So the patient responded
either with the left hand, the right
hand, or verbally. And now the thing is,
you would expect that if the basic--the
anecdotal evidence is true, that when a
stimulus appears in the left visual fields,
the patients should be fine, indicating
the presence and location when he
responds with the left hand, but not
when he responds with the right hand or
verbally. However, that's not at all what
we found. So I didn't put false alarms
here, but basically these were
non-existent--between zero and five
percent. So when it was nothing there,
the patients always said, "I saw nothing."
Yet--but let's just highlight one thing,
like the verbal reports. Here you see for
both patients when the item appeared--
when an item appears in the left visual
fields,--so this is the important thing
here, in the left visual fields--he never, zero
percent of trials, he never said, "I saw
nothing."
Never. He always indicated that he saw
the stimulus, and he was pretty accurate
indicating where it had appeared,
actually. Okay, this is about the study,
you can find in the paper we published
last year in Brain. And there--we
did all kinds of controls, with all kinds
of different objects, [inaudible] stimuli,
confidence measures to show that he has
accurate metacognition, it's not
blindside, basically. And the interesting
thing is--and I don't know if this was
mentioned--I think Lizzie kind of referred
to it. When you look into the literature,
there are some papers that don't
explicitly look for this, but they have
some quantitative data on what on the
effective response type, and basically--ok
I'll go faster--and basically what they
find--basically they find same thing.
When you look at this in a quantitative
way, you basically never find a role for
response type. So basically the anecdotal
evidence just does not hold up.
[inaudible audience remark] What? 
[inaudible audience remark]
Oh yeah, sorry. These patients were two split-
brain patients with complete splits.
Both their corpus callosum was
completely cut, and in one the anterior
commissure was cut as well.
Ok, so for an overview of these
literature way where they find the
same things that we find--yeah. You can
find this in the Trends in Cognitive
Science paper--cognitive psychology,
not cognitive science, that were published last
year as well. Ok, so what is the
conclusion? Ok ,so basically
everything lines up: the person himself
says, "I'm not two people," the people close
to him all say he's not two people, and
if you do rigorous quantitative studies,
you also find evidence, well he can
respond to stimuli throughout the entire
visual fields with all his response
types, so really he is not two people. So I
think all the evidence basically points
in the same direction. Ok, so what does it
mean in model sense? This is the old
model--oh, ok, whatever. This is the old
model: so there's one hemisphere, there's
one person; other hemisphere, there's another
person, and they both see--have the visual
field and control half the body. And I'm
saying, no no this is not the case.
There's one person experiencing the entire visual
field, and controlling the entire body.
But there is a caveat here; that's why
this split perception is indeed
split. There is one person experiencing
two unintegrated streams of visual
information. Because indeed, as David
pointed out, and basically what Elizabeth
also pointed out, these patients--and this
also what I found in these patients that I
tested--they cannot compare stimuli
across the midline. So you may wonder,
well but it's still very strange;
why did it feel normal if there's two
unintegrated streams of visual
information? Well, you basically just
experience that when you did the MOT
test. Both your hemispheres were
processing the visual information
independently and as you introspectively
could tell, I think, this wasn't so
strange. And that's why the patient feels
normal, and comes across as normal.
Okay, and yeah, again, I refer to
TiCS paper for more detailed explanation
of the model. Okay.
And hopefully I'll go through this
quickly, and Joseph is, of course, the
moderator her--or, let's say, the in-between 
position. And he had a very interesting study,
which i think is very important, which,
really, I think is one of the best papers
arguing for the two person or
for split-minds view. And what they did
is, basically, they have faeshed words in
the left visual field or the right
visual field, so they presented words
effectively to the right hemisphere or
the left hemisphere, and then they asked
the patient to rate what he thinks
about these words. So how much does he like
what is shown to him. And the interesting
thing is--and I think this is very strong
proof for a two-person model--is that the
left hemisphere had completely different
preferences than the right hemisphere.
Okay. And of course this is not compatible
with a one-person view. So this is the
actual data, and you see a very big
difference between what the left and
right hemisphere... There were two sessions; 
this is the data from the first session. However, I
think there is something funny about
this data, because I hope you can see
that here--here it says 'Paul', which is his
name, and when he responded with the left
hemisphere, he really likes himself, but
when he responded with the right
hemisphere, he basically hates himself--
was as negative as possible. Okay, it is
possible, you know, it could happen. But
here is Fonz--
the Fonz from Happy Days. And with the
left hemisphere he really likes the Fonz,
but with the right atmosphere he hates
Fonz--I mean, who hates the Fonz? That's
impossible.
No, but that's--I'm actually trying...
You see for other things: mother, sex. But
also the same pattern: with the left
hemisphere he really likes it, with a
right atmosphere almost maximal dislike.
And even for the word 'nice'-- the word
'nice' is, of course, objectively nice, but
still with the
left hemisphere he really likes it, and
with the right hemisphere he doesn't. So
I'm a little bit suspicious--yes, one
minute--I'm a little bit suspicious of
the data, where I'm thinking, maybe he
didn't understand the instructions
completely correctly, and maybe he just
thought he had to give symmetrical
responses based on where the stimulus
appeared. And, indeed, in the second
session, where there was a five-point
scale, basically they find completely
different data. Now he really likes
himself, doesn't matter how where the
words appeared; and he also really likes
the Fonz. So, I would say--yeah, not to be
too critical of Joseph's study, but--no, I
think this is conceptually a great study,
and this is the kind of study we need to
do--but I just think based on this data
we don't really know for sure that each
hemisphere has its own preference. And
that's what I want to end with. So, okay,
we can debate this which is very good, I
think, and hopefully we can come up with
good ideas. But the good thing is these
patients are still around: we can get
more data to push the ball forwards, and
that's exactly what I want to do. So
a study I have planned,
it's basically interrogate the patients,
but then directly interrogate the
hemispheres for some technical reasons,
because when they gave overt responses
--yes, I'll finish up--when they give
overt responses, there's some other
things that can cause seeming unity when
there really is no unity. Okay, so I'm
basically going to use an Adrian Owen
kind of paradigm, where the patient
responds by visual imagery. So he
imagines playing tennis or walking
through his house, which you can decode
on a trial by trial basis. So basically
you can ask, for instance, "okay, what do
you prefer--pizza or pasta? If pizza,
imagine playing tennis. If pasta, imagine
walking through your house. And the good
thing is, we present these questions
auditorily, which go to both hemispheres
at the same time. Both hemispheres
understand simple language, and 
now we can decode immediately, and we
do a wide variety of questions also, like,
"pick a random number," and so on. And now
we can decode, do both hemispheres--each
hemisphere, does it have its own
preferences? Does it give its own
independent answer? Or do the hemispheres
together basically all the time give one
answer. And I would argue if we find the
latter, then it would support the 
one-person model, and otherwise, of course,
clearly it would support the two-person model. 
Ok, this is a future study, haven't done this yet,
so we don't know what comes out of it.
But I would say, for the moment,
just to reiterate, everything points to
one person. The person
himself, that people around him, and the
rigorous quantitative studies. Alright
thank you for your attention.
[Audience applauds]
Chalmer: Okay! Our third speaker defending an
intermediate view from the Centre for
Neural Science here at NYU professor, Joe
LeDoux!
[Audience applauds]
Joe LeDoux: Alright, let me get a--have a second to
pull up my slides here.
[Audience laughter]
Okay. Where's--how do I get the
the--get rid of the presentation?
[inaudible]
LeDoux: Alright, don't worry about it. 
I'll just do it like this.
Alright, well--so, I haven't done
this kind of stuff for 40 years, so I'm
gonna be reaching back in memory banks a
bit, and I want to--you know I think that--
as we just saw, I did some studies that
are directly relevant to this, a long
time ago. They were all "anecdotal", as he
mentioned, but, you know, I think that
there are some things to think about
from the beginning. One is that, you know,
you've got a brain that's been split in
half--
at least the forebrain is split in half
now, and one thing I don't quite
understand about the the last point was
that--how was the, how was the person-- how
was the speech being generated for
visual information that isn't in the
left hemisphere. And in our patients, I
think there's an answer for them, but let
me just go on and tell you what I have
in mind here. So the first thing I want
to just mention is, one of the things we
were able to do in these patients was--so
Mike Gazzaniga had studied split-brain
patients in California with Roger Sperry
in the 60s, but in the 70s he had moved
to Stony Brook and there was a new set
of patients being operated on at
Dartmouth. And so we had access to brand
new patients to kind of look at some of
these issues again. And in these patients, we
were able to test them before surgery
and right after surgery. So I had only
been
in the lab a few months when Mike sent
me up to Dartmouth to go test this
kid--young teenage boy--before the surgery,
and then to meet with him afterwards and
do some other stuff. So right after the
surgery, in the
hospital room, a day or so afterwards,
he's up and alert and talking, and we're
just kind of chatting about how's
feeling and what's going on and so forth,
and all of a sudden you see one of the
classic things that's been reported: his
left hand goes out as the nurse
passes by and he grabs her on the behind,
and the right hand pulls the left hand
back. And that really has stuck with
me. It's been a long time but I just
still have a very profound visual image
of that. It's very anecdotal, I admit, but it was a
very kind of dramatic thing. And there is
this thing called the acute
disconnection syndrome, where you get the
most dramatic effects, especially in the
first weeks and months and years right
after the surgery. So that brings me to
some of these questions about
generalizing, and I think that there's no
such thing as a typical slip-brain
patient.
Lizzie kind of mentioned that as well.
Each one is different. So they differ in
terms of the locus of the epilepsy in
their brain: left hemisphere versus right
hemisphere; within the hemisphere where
the where the epilepsy is located: is it
in the temporal lobe or in neocortex; the
age when the surgery was done :the
younger the more reorganization that
follows. Reorganization over time,
especially language, is known to exist,
but perhaps many other things get
reorganized. I mean, you divide the brain
in half. In a teenager the brain is still
developing and rewiring and so forth. And
so you're gonna expect some kind of
plastic changes. I mean, language
supposedly doesn't change too much after
the age of 12--or at least that's what
they were saying back in the 1970s, I
have followed all this that much. But
other things we know continued to be
modified: prefrontal cortex, for example,
you know,
still developing in 22 year-olds. So,
third thing is the interval between the
surgery and the behavioral test is
important. So this with this acute
disconnection syndrome, if you see most
dramatic effects early on, and then less
dramatic effects as time goes on, I think
your patients--or several decades into
the process here. And gender. I mean
supposedly--again, my knowledge is
is old, I haven't followed the
lateralization stuff, but back then it
was said that females have more
bilateral organization, especially of
language. But again, brain damage can move
things around. And all of these people
that we studied typically had epilepsy
since very early in life, and so you have
this congenital change in the brain that
is rewiring the brain from the earliest
days of childhood, so a lot of things can
go on that don't necessarily go on in
the typical brain, which is why I think,
you know, the fact that we can
demonstrate some things such as divided
attention in the normal human brain,
doesn't necessarily mean that that's
what's going on in the split brain. So
there are also conceptual issues: what do
we mean by minds or consciousness? This
will affect the answer to whether
consciousness can be split. So,
perceptual control--we seem to agree that
perceptual control is perhaps split. But
whether self-awareness is different is
another issue. And then a methodological
issue: how much is the absence of
language in the right hemisphere of many
of these patients
a factor that prevents you from
assessing consciousness and
self-awareness, as opposed to whether
it's demonstrating that there was an
absence of consciousness. So in my thesis, called "The Split-Brain and the
Integrated Mind", I studied this one
patient, he had long-standing epilepsy;
surgery as a teenager; he was tested
extensively within the first two years
following the surgery; he had the typical
sensory motor separation;
the capacity to speak was confined to
the left hemisphere, but the right
hemisphere could comprehend both written
and spoken language. So this was an
unusual case. And this seemed to be a
case that we could test that the
question of whether language does
something for the right hemisphere in
terms of conscious awareness. So here's
the the typical thing: the brain is split,
corpus callosum is sectioned. In the
these patients the corpus callosum and
anterior commissure was usually gone. So
the left hemisphere talks to you, seems
clearly conscious. The mute right
hemisphere is less clearly conscious, and
then we have the assessment problem: is
it due to language or not that you can't
find some critical evidence of
consciousness in the right hemisphere? So
we designed a study, where one of the
things we did was we would present words--
part of the question to the left
visual field--sorry we would speak part
of the question, say "who", and then we
would put "are you" in the left visual
field going to the right hemisphere,
because he could read over there. And so
the left hand comes out and spells 'Paul'.
So the right hemisphere knows his name,
and it's the same name as the left
hemisphere. So that kind of goes with the
unified consciousness idea. When you say
"what did you see," you're talking to the
left hemisphere, he says" nothing." But the
left hand goes out and and spells his
name hen you force him to pursue the
thing. So in some sense the right
hemisphere and left hemisphere both have
some kind of sense of self, since they
can, you know, name the entity that
they are--the name that they
go by as a person. But they also had, in
this case seemed to have, different life
expectations, plans, and hopes
for the future. So the left
hemisphere wanted to be a race car
driver,
the right hemisphere wanted to be a
draftsman. So, you know, is this, like, you
know, really hard data? No, it's an
observation, anecdote that we got in this
one patient. But it's a piece of
information that we obtained that's kind
of interesting, that you think about, you
know, answering the question, "what do you
want to be," and two hemispheres have
different ideas about that. Now another--
so, again, the question is, is language
necessary for this, or is it just helpful
in assessing it? So here's another
example.
Left hemisphere--Mike has shown this
quite a bit, it's been in all the
textbooks too--left visual field sees a
snow scene, right visual feel a chicken
claw. You tell them to you know point to
what you saw,
left hand points to the chicken--
sorry, right hand points to the chicken,
left hand to the snow, to the shovel. And
you say, "why did you do that?" So he says,
"well, I saw a chicken claw, so I picked a
chicken. And you need a shovel to clean out
the chicken shit." It was a country boy, so
this was part of his understanding of
the world. So, the idea that we walked
away with from this is that the brains
in a split-brain--in this particular
split brain patient--the brain is
separated. There's some kind of mental
separation, to the extent that one
hemisphere doesn't always know what
information is in the other hemisphere.
But there's a strong compelling sense we
have to put it all together and to make
sense of it. And the way he did that was
by, you know, generating a narrative that
explains why his behavior was produced--
or why he produced that behavior that he
didn't produce in a sense.
Again, we're talking to the left
hemisphere when we get these
narratives out. So we thought, well maybe
this is kind of like what happens in all
of us all the time, that we--our brain is
full of different kinds of systems that
cause us to respond in a certain way, that
isn't necessarily part of our conscious
control process. But what we do to make
sense of it is we monitor our behavior,
we're using what we would call "working
memory" today--that wasn't such a popular
idea back then. But we monitor our
behavior, and then we use that
information to generate a kind of
explanation or a kind of continuity to
our life over time, to make sense of it
and to explain who we are as an
individual, And in the split brain
patient, in this patient, that was
important because of the lack of sharing
of information, but in all of us we have
other systems that generate stuff like
this all the time. This was the the
emotion rating test that was mentioned.
I'd actually even forgotten about--so
long ago I forgot about the first set of
day that you presented, and so this is
only--I'm showing you the second
part of that, second table. But where we
see the two hemispheres are actually
rating everything the same, except
for the word 'Nixon'.
[Audience laughter]
I won't go there.
But what's going on here, though,
is that the left hemisphere is verbally
rating these things--these words--on the
basis of either having seen the word
itself, or on the basis of a word seen by
the right hemisphere. He can't tell you
what the word was, but he can give a
rating that matches exactly what the
left hemisphere got. So you could say,
well that's evidence for unified
consciousness as well. And, you know, the
question is, how was this being done? And
that's again the question I have about
how the information that's perceptually
isolated in the right hemisphere can be
talked about? Well, in this case in these
patients, there's an explanation in this
patient. So here in the normal brain the
information goes over and he can say
good or whatever. But when the brain is--
so when the brain is split, you can't. But
in these patients with the anterior
commissure, which connects the 
amygdala to the two sides of the
brain here, we've hypothesized--we knew
about this from reading the work of
Pierre Glore and other people who had
been studying epilepsy and found
some evidence for the amygdala being
involved in fear and other emotions at
the time, and there were other kinds of
animal studies suggesting rats with
amygdala lesions didn't learn avoidance
responses very well. So all of this kind
of pointed to the amygdala, some kind of
vague emotion processing centre. So the
idea the we came up with is
that the visual information, perceptual
information in the right hemisphere,
activates the amygdala in the right
hemisphere. The right amygdala sends
information to the left amygdala and
then the left hemisphere speech centre
reads that information out, and rates the
word, but it doesn't have access--the
anterior commisure doesn't present the word
itself, only the rating, only the the valence of the
word. So that's what set me off
getting interested in the amygdala, and
what I've been doing for the last forty
years. So, let me just close off going
back to these issues that I think are
important to keep in mind, that each
patient is different: where their
epilepsy is in the hemisphere and
between the hemispheres differs; the age
when the surgeries done is very
important; the interval between the
surgery and the tests is important; and
maybe even the gender of the patient. But
we were mainly studying male patients at
the time. So I'll in there. Thank you.
[Audience applauds]
LeDoux: I'm sorry, I forgot to--
I just want to say this.
Disclaimer: for me these observations of
a single patient were just a source
of inspiration about what to do.
Gazzaniga and I wrote a book called the
integrated mind, and we had two ideas in
mind there: one is that the first set of
split-brain patients were all about what
happens when you take the brain apart.
With these studies [what] we were doing was
trying to understand the implications of
that for the normal brain, so we called
the book "The Integrated Mind". And the
other reason we call it "The Integrated
Mind" was because of this compelling
sense that the patient seemed to have
put it all together despite the fact
that he didn't have all the information
to put it together.
Chalmers: And one mind or two?
LeDoux: This patient one. The
others, it depends. That's why I say it's
complicated.
[Audience applauds]
Chalmers: Okay! So now we'll have a round of 
quick responses; five-minute each.
Is anyone gonna use slides for their response?
Schechter: I actually will use one slide, if that's alright.
Okay, thank you so much. I have a lot to
say, obviously. First of all, I'm glad
that Yair brought up this study by LeDoux,
Wilson, and Gazzaniga. I actually talk
about this in my book as well. And I
agree that--so, as I say in the book, it
looks as though R or Righty was a
little confused when it redid the Fonz
negatively. I will note that the
responses were being given by pointing
to numbers labeled from one to five, and,
a little confusingly, from my perspective,
one was high--one represented 'like very
much'--and five represented 'dislike very
much'. And I think that R got a little
confused about the reading system. For
the second series, where the answers were
convergence, they also attached verbal
labels to the number. So one now
said 'like very much' and five said
'dislike very much'. And now you got some
converging responses, instead of what
seems to be these you know very
different
perspectives on different issues. But,
personally, I don't see why it matters
how similar the preferences of the two
hemisphere systems are. My sister and I
have a lot in common. If you asked us
questions about our preferences and our
likes and dislikes, we would give very
converging responses, but we're two
distinct thinkers. The question is how
our mental states interact with each
other, not how much we have in common.
Similarly, and I think this is probably
the major difference between Yair's
perspective and my own, I actually don't
think it's central to the issue whether
or not the very same kinds of motor
behavior are under control of different
hemispheres or the same hemisphere. So
this is a figure from the TiCS paper
by Yair and colleagues that he cited. And
the top panel is supposed to demonstrate
the two mind model of
split-brain subjects, on the bottom panel
the one mind model. So, note that it's not
just perception that Yair and
colleagues admit is divided between the
hemispheres, but cognition also. You have
to recognize this in order to explain
the results of the cross matching
experiments, where distinct stimuli are
presented to the two hemispheres, and
then the subject is asked to say whether
they're the same or different. If you think
about it for a second, if you are
presented with a star and an axe, it
doesn't matter if you can't in a unified
way perceive both of them. As long as you
know that one is a star and one is an axe,
you can adequately answer the question,
"are the stimuli the same or different?"
But knowledge is also divided between
the hemisphere systems. So the question--
the reason--you know, Yair and I would
both concede, I think, you know, the top is
a representation of the two mind model.
The question, I think, where we disagree,
is whether the bottom panel necessarily
represents a one mind model. From my
perspective, if it turns out the right
hemisphere and left hemisphere mental
states all kind of ultimately--the
products of these all converge on a
common set of effectors, a common set of
motor responses, that would not be
sufficient, in my view, for there to be
one agent or thinker in the split-brain
case. So the relevant question is going
to be, what kind of integration of mental
states is occurring at this stage? Okay,
so, I accept Pinto and colleagues'
findings, and I think they're, you know, I
think, they're surprising and important. I
think that this is a little hard for me
to respond to now because I suspect that
the devil's in the methodological
details, in terms of what these--not that
there's any problems with the experiment--
but in terms of what they can actually
show about where integration of right
hemisphere and left hemisphere mental
states are occurring. I will note that I
view these results as broadly falling
within the debate that occurred in the
1980s and 90s, especially in this brain
literature, on the reunification view. And
this literature from the 1980s and 90s,
which is vast, concerned
essentially what kinds of
inter-hemispheric interaction there is in
split-brain subjects, and when you're
observing inter-hemispheric interaction,
versus, again, the hemispheres both kind
of taking turns, controlling certain
behavior, and so on. And there was a lot
of interesting debate trying to pick
apart like, again, are you actually seeing
inter-hemispheric interaction, or--thank
you--or are you seeing the fact that both
hemispheres can perhaps use the right
hand or the left hand. The most
interesting issue, I think, Yair brings up
is--at least I think this underlies the
major objection to the two thinkers
claim--so if there really are two
thinkers there, why don't the subjects
realize it, why don't their friends and
family members realize it. I will say
that I think, you know, people don't
realize they have unilateral neglect,
either, but we don't think that that
means unilateral that neglect doesn't
exist. It's unclear, in fact, that
introspection can reveal to the subjects
that they share their body with another
mind. We don't introspect other minds. We
know that other minds exist because we
observe other animals, and because we can
speak to them--well, by a hypothesis,
there's only one speaker in the split-
brain case, and there's one face, one pair
of eyes. I do not think it would be--plus,
it's just a very radical conclusion. What
would it take for you to accept that
it's not just that you're sometimes not
in control of your behavior, that you
sometimes say things you didn't mean to
say, but there's actually some other guy
saying it inside you. And I think
similarly with second parties, they can--
from the literature we have on this,
which is pretty limited, they can
obviously tell that something strange or
different about the subjects after the
surgery. But again how would they realize
that there were two distinct thinkers
there, unless they've seen the
experimental evidence, demonstrating that
would often looks like unified behavior,
in the same way that the behavior of
conjoined twins Brittany and Abigail
Hensel is very unified, it's actually the
product of, again, mental states which
aren't integrated in the way they
characteristically are within a single
mind. Thank you.
[Audience applauds]
Chalmers: Okay, Yair.
Pinto: Yeah, so I didn't take any notes; I forgot to bring my notebook. So
maybe it's a little bit disjointed, my
response, but let's go from my--from what
I remember. First, to respond to Lizzie.
Well, some very interesting points there,
of course, and the idea with 'sky' and
'scraper' not being integrated--I think
this actually can be explained by
something less radical than there being
to people, and that's basically what I
show here in this model as well. Just the
visual information is not integrated. So
there's two independent streams of
visual information that don't get
integrated, that's how you can explain
these results. Then about--yeah, here about
cognition. Yeah, it's very good that Lizzie
Lizzie pointed it out. This is kind of
confusing, because indeed if I said that
everything is split, except for the
control agent, then that becomes kind of
a vacuous term. So what I mean here is
that higher-level cognition should not
be split. So it should not be the case
that there's two streams of independent, 
conscious thoughts, or indeed
there's--the two hemispheres have their
own preferences and their own ideas. And
to elaborate a little bit more on that
experiment--because both Lizzie and Joe
went into that--okay, so how
 could that work, and how can you
distinguish? But one of the questions, of
course, is going to be something like
pick a random number.
So even--although me and my brother are
also very much alike in preferences, if
we are, at certain points, at the same
time, to pick a certain number, a random
number, it's very unlikely that we pick
the same number all the time. That's
why these kind of questions are in there
as well. And then
 Joe's point about how the right
hemisphere was supposed to understand
language? Well, yeah, as lesion literature
also of course reveals, you can--the
right hemispheric cannot produce language,
but it should be able to understand
simple language. You also find it in
people who have lesions in their left
hemisphere, which affects their language
centres, they have problems
producing language but generally they
can understand simple language.
I think this covers most of the grounds.
A complete show--okay, so some of the
anecdotes that Joe mentioned. Of course,
these are extremely compelling, so this
would check out indeed, like one hand
fighting the other, etc, etc. If we can
quantify this, yeah, I would throw in the
towel. I would say yes, you're right, there
are two people in there. It's just a
thing that when I have done my
quantitative studies so far, it
just didn't check out yet. This
doesn't mean that these are not the
right ways to go, or the right questions
to ask. I completely agree this is what
we should be looking for. But so far we
haven't found it yet. But yeah, if we do
find it, for instance in this imagery
experiment, or I'm also thinking about
metacognition experiments, where the
patient basically performs a primary
task with the left hand or the right
hand, and then has to verbally indicate
confidence or something like that. Indeed,
if metacognition is split, this would
also support two-person view. Then the
other point is, yeah, all the patients are
different. Yeah, maybe, and it could be
indeed that patients that I investigate,
they have undergone surgery decades
ago, so I cannot clearly test them right
after surgery. Yeah, so we don't know. It
would be great if we can find patients
that are closer to when the surgery was
done, to know whether indeed there's some
kind of acute syndrome, where
there's really two people that somehow
unify. And yet--that's also why I think these
kind of debates are really good, because
then we have to think about, what are the
good tests to do? So imagine, we do
encounter these patients, and what are
the tell-tale tests to know that there
are either 1 or 2 people. And my claim
would be, it's really about higher-level
cognition. So if we look at lower level
perception, yeah, I think we
all agree, that's split in split-brain
patients. But I think we can argue that
that's actually not so
conclusive when it comes to whether
there's one or two people. But when
higher-level cognition is split, yeah, then
I think we could make the case that
there's really two people there. And you
could do this with visual imagery
experiments, metacognition. We're also thinking
about doing a resting state
experiment. So I think what helps here is
imaging experiments. Not because I'm anti
--yes, thanks--
anti-overt behavior, but just because the
things that Joe mentions--yeah, I basically
never find this in overt behavior. And this
is also something that's--a lot of
researchers claim that yeah, overt
behavior seems very unified. There's lots
of reasons why that could be: cross
queuing, subcortical connection, and so on.
But, of course, yeah, it would be the best
we just have a behavioral paradigm with
the left hand and the right hand do
completely different things or start
fighting each other. But it basically
almost never happens, so that's why I
think, yeah, for the future we should
probably do more neural experiments,
where we directly test what happens on 
the cortical level. I think I'll leave it at that.
[Audience applauds]
LeDoux: Okay, well, I don't have much to add
beyond what I said earlier. You know,
I think one of the points that I find a
little confusing in our discussion is
that we've been using mind and
consciousness and cognition rather
loosely, and I think that without being
very precise about what--and self and so
forth--what we mean by those terms, it's
hard to know if, like, the absence of
perceptual interactions versus
"high-level" cognitive interactions versus
even higher kind of stuff involving the
self is really split or not split. It's--I
think even just calling upon higher
cognition is not sufficient, because, you
know, that covers a lot of territory. I
do agree that if there are apparently
patients still being done somewhere--
someone told me that recently, I don't
remember exactly who and where it's
being done, but this would be the
opportunity to apply more rigorous
rigorous methods on these new patients,
and maybe get at some of the things
that we weren't able to get at and
didn't even know we should be getting at
40 years ago, when we were just trying to
get some anecdotes about all this. So I
think I'll just stop there and maybe we
can open it up.
[Audience applauds]
Chalmers: Great, let's get all 3 of you up here.
Just to start with, maybe we can see
if any of you have questions for each other.
LeDoux: I think we just did that.
Chalmers: Okay, well,
that was responses to each other.
One thing I'm curious about
is on the question about if there are
two minds why don't we see it.
What happens if you asked these
subjects, you know, is it like half the
body that you're not in control of. Or
what if you, say raise your
left hand if you feel like you're
trapped in this body without much
control of your speech.
[Audience laughs]
Do you ever get that result?
Pinto: Yeah, that's
why I said we have to go to imagery,
because--yeah, I haven't asked this
specific question, but I'm guessing that
that wouldn't work.
Chalmers: It's especially a question
for Lizzie, since it's a potential 
problem for the two minds view.
Schechter: So, I think part--yeah, so the second half of the
book is essentially--I mean it's largely
devoted to explaining if there really
are two thinkers composing some of these
split-brain subjects, then why don't they
seem to feel like two subjects. And
obviously it's a little hard to tell,
with Righty, what's going on,
given that Righty can't speak in full
sentences. But from what we can tell,
no, Righty's equally ignorant of Lefty's
presence as Lefty is of Righty's. And it
is, you know, prima facie puzzling. So I
actually don't think that either of them
is just--there is lateralization with
respect to proprioceptive information
and with respect to motor control and so
on. But neither of them should be wholly
paralyzed or wholly numb for an entire
half of the body, so I think we can kind
of rule that out. And I think given that each
of them enjoys at least partial control
over, you know, all limbs, and it receives
some sensory information from all limbs,
I don't think it should feel to either
one of them as though that part of the
body is wholly not theirs. You do still
need to explain, I mean, given that righty
by a
hypothesis is hearing Lefty say all
these things that Righty is not saying,
why wouldn't that be sufficient for
Righty to--and I think, again, part of the
answer here is, you know, we usually don't
choose our words that carefully before
we speak.
You know, we self attribute the words
that come out of our mouths anyway,
regardless. And I would also add, I think
that these subjects are a little special
because of their long histories of
severe epilepsy. They are unusually used
to not feeling fully in control of their
bodies or behavior. And so it's possible
that they're a little more willing to
kind of roll with the punches of, you
know, saying things that maybe they
didn't totally mean to say, than you or I
would be.
Chalmers: Okay, let's go to the audience. Ned.
Ned Block: So, you mentioned that in the--what you 
call I think "acute disconnection syndrome"
at the
very early stages of these patients, so
maybe the two minds case is especially
strong in the time of that acute
disconnection syndrome. I mean, could
anybody deny that in that period there
are two minds? LeDoux: Well, I think
if it exists it would be especially
strong in that time. Block: So it's not 
general agreement about the acute
syndrome and that initial--
LeDoux: All we have are anecdotal observations
like the one I mentioned. Block: but nobody's
 done rigorous testing in that period?
LeDoux: What I was talking about happened in 
the first couple of days, they're still in the
hospital bed, you know, their head is
wrapped, their skull had been opened, so
they're not ready for, you know, going
into a testing area. But in a sense,
you know, the acute dispute
disconnection syndrome is not, you know, a
week or two weeks, it's just something
that dissipates over decades, so it's--you
start acute with dramatic effects, and
then it dissipates as you go over time.
Block: Maybe that explains Yair's result--
LeDoux: I think that it could.
We don't know unless we could
test patients from the start, and I think
if we had those patients now, 
we would have a much better
perspective on how to do it, you know, second 
time around you know a little better.
Schechter: You first.
Pinto: I think it would
be great to test these patients from the
start. You mentioned that there are some
of these patients around, but yeah, so far
I've had a really hard time finding them,
actually. And yeah, the operation is still
being done, but generally on people
with an extremely low IQ, so like IQ of
around 25. And then you cannot
really test them. So that's basically--I
think the challenge now is just to get
patients-- LeDoux: And more likely that 
they all had the complete splits--
Pinto: Yeah, they do. 
You first do partial splits
and you wait, and if that doesn't work, etc. 
Schechter: I mean, I just want to say--I
want to direct people's attention again
to the really sizable empirical
literature of the 80s and 90s that was
in part inspired--largely inspired by this
recognition that some of the early
results were getting increasingly
difficult to obtain with these split- brain
 subjects. That they were now better
able to respond to right visual field
stimuli with their left hands than they
had been able to previously. And this
literature was designed to--the goal was
to try to figure out why this was why
that was happening.
For instance, one possibility is, oh
suddenly, you know, vision has become
integrated across the two hemispheres.
Maybe what's seen, or what's shown, in the
right visual hemifield is now available
to, you know, the right hemisphere as well,
and not just the left hemisphere. Another
possibility is that each hemisphere is
gaining--each hemisphere system is
gaining an increasing ability to control
movements of both hands. And this is, you
know, this is what this literature was
looking at. And you know, it found kind of
a mix of both: so there were certain
respects in which there appeared to be
more inter-hemispheric integration, but
there was also a lot of evidence for--I
mean, for instance there is some really
interesting, admittedly very difficult, studies
designed to figure out whether a
capacity for right hemisphere speech was
emerging in certain split-brain subjects. And
the tentative conclusion that was
reached--obviously it's hard to tell when
you have one mouth and one set of vocal
cords and you're not using neural-imaging
for the most part either--but the
tentative conclusion that was reached
was that yes, some of them had learned to
speak out of their right hemispheres and
some of them didn't. So, in LB, for
instance, the general conclusion was that
he didn't seem to have learned how to
speak out of his right hemisphere, but
with PS and JW, the tentative conclusion
was that they developed the capacity for
very limited right hemisphere speech
under certain conditions.
Chalmers: Okay, let's go to Antonia.
Antonia: So my question
is mostly about the significance of the
terms 'mind', 'person', 'consciousness', 'thinker',
and 'animal', all of which I heard in
different contexts. So I just want to
invite each of you to say a bit more
about what those mean in your mouths, and
then also what the upshot is, if maybe
there are two minds but one person, or
two minds but one animal in these split-
brain patients.
LeDoux: Well, I mean I've pointed
that out but I didn't say what I
meant. But, you know if we start with 'mind',
we can think of mind as being partly
conscious and maybe partly non-conscious,
and when we talk about consciousness we
have to think about awareness of stimuli,
versus awareness of our emotions, versus
awareness of our self, awareness of
others. And so I think
each of those needs to be addressed
empirically, rather than just taking the
word 'mind' or 'consciousness' and trying to
study it the way we did back then.
Schechter: Yeah, great question.
So, the book is organized
largely around kind of separating these
issues, these capacities,
but they're all so closely connected,
ultimately. 'Animal'--I just assume that a
split-brain subject is one animal, and
that the criteria for something's being
an animal versus being two animals is
biological rather than psychological. You
could dispute that, and obviously there
are hard cases, again like certain cases
of conjoined twins: are there two animals
there
or one animal with a partly divided body?
But I just--I take it that the split-brain
subject is one animal. 'Mind'--I take it
that to have a mind is to have a certain
set of capacities. And so my argument
that a split-brain subject has two
minds is an argument that there are two
physical systems--again, very large, each
one almost the whole animal--each of
which has these capacities, and again
these capacities are causally defined,
and so you have to look and see, what are
the actual systems that have these
capacities, and are these capacities
operating inter-hemispherically or only
within each of these hemisphere systems.
Consciousness is harder. You know I
think of consciousness largely in causal
terms, but there are mental capacities
that aren't the capacity for
consciousness, so now you're looking at
kind of like a subset of capacities, I
think, when you look at consciousness in
order to determine whether consciousness
is unified or disunified or unitary or
dual after split-brain surgery. And then
finally 'person'--I mean, this will
probably--amongst philosophers, this will
be the most radical claim of the book,
probably. I argue that there are two
thinkers but in fact one person. So a
person is a very special kind of thinker,
with a very particular set of capacities.
And I won't--it's not as relevant here
today since we're talking about minds.
But one of the capacities that persons
have is the capacity for
self-consciousness. And along with this
capacity for self-consciousness is the
ability to distinguish yourself from
other self-conscious thinkers. And I
argue that R and L lack this ability to
distinguish themselves from each other
because they share one body, and that
this ultimately makes them parts of one
person.
Pinto: Yeah, okay. I think what I mean by
it is basically an experiencer. So the
question is, then, are there two conscious
subjects there or just one conscious
subject? So what is it if there's two
conscious subjects? That's basically what
I tried to sketch during my short talk.
Then there's one person in the left
hemispheres who sees half the visual field
and controls half the body, and there's
another person in the right visual--
in the right hemisphere 
who sees the left visual
field and controls the left side of the
body. So it's really two independent
conscious agents--that's what I would
call split minds. And unified minds I would
just say, okay, just one person, one
experiencer, even if not all the
processors are automatically
integrated. So in a way, like, if you see
an out of sync movie, you cannot connect
the dots, but, yeah, you're still one
person. So I think that's mainly how I
would define it. And then of course
the challenge is, how do you measure
that? Because it's like a first-person
definition, and there are only third-person
means to look at that. And that's why I'm
thinking of, like, okay, neural things or,
like, higher level cognition things. Yes,
okay, I think it's acceptable that you
have one person with somewhat split
streams of perceptual information.
But to imagine that there's one person
who has two independent streams of
conscious thought, for instance--that
seems less likely. Or has two independent
sets of preferences--I guess it's logically
possible but, yeah, I would be more
convinced then that that's different.
Chalmers: Okay, let's go to Rob. 
That Rob, sorry. Rob at the back, there.
Rob: Higher order thought has been 
mentioned a couple of times,
higher order cognition, I mean. Metacognition
was mentioned briefly. And I wonder
how much data there is on the use of, say,
learning strategies. Or, you know, if you
can deliver a request only to Righty to
memorize some information, and you can
deliver a request only to Lefty. Do they
use different cognitive strategies?
Closely related to this is a question
about executive function. Do you get, you
know, different dispositions toward
executive control, different styles of
executive control, when you ask Righty 
to do something, then Lefty. And I
ask this because these are the things, at
least in the cognitive domain, we
associate most closely with who you are
as a mind, right? So take out affect and
consciousness, and that's where stuff, you
know--your metacognitive and
executive dispositions.
Schechter: Yeah, thank you. So,
I mean, I know of some evidence that, you
know, there are two working memory
systems. I don't know--it's a really
interesting question, like, whether they
seem to have different learning styles. I
would assume that you see somewhat
different learning styles, and I think
you would agree with this, because 
Yair agrees  that there are these
hemispheric differences. Of course, you
should maybe see some weak kind of effects
in a non-split subject, too, maybe
demonstrating these sorts of differences.
But I haven't really looked at that, I
think--and that's mainly because, again,
from my perspective it wouldn't matter
if the two hemispheres systems were
totally identical with respect to their
learning styles and, yeah, perceptual
processing styles and so on. The issue is,
again, one of interaction.
Pinto: Yeah, yeah, no, I think,
I think this is actually one of
the first things they did, is looking at
perceptual learning in animals. But it's
completely replicated in people. So yeah,
there is independent learning per
hemisphere, but, indeed, as Lizzie says, you
actually also find this in healthy
adults. So if you do a statistical
learning task, for instance, with the
Eriksen flanker task, you will learn
certain--yeah, [unclear] who also did a lot 
 of split-brain research actually published this, I
think, like ten years ago or something.
You find that you learn certain
interference patterns--I don't know the
exact study now, but it's also
independent per visual field. It doesn't
transfer from one hemisphere to the other.
So, perceptual learning can also be--and,
yeah, sorry, I'll let you go then--working
memory--I also did some of these studies
myself, and I think there are multiple
studies on this--working memory also
seems to be entirely split in split-brain
patients. So it seems that each
hemisphere has its own working memory
capacity. And metacognition, yeah
 there's not so much on that, but
yeah, I want to look into that
more, actually.
Schechter: Yeah, I mean--so, I do
believe that perceptual learning goes on
separately in the two hemisphere
systems in a way that it doesn't in non-
split subjects, but, again, if the
question's about different learning
styles, I don't know that literature.
Chalmers: Okay, we'll go to this Rob.
Rob #2: Yeah, so this is primarily a question for
Liz about your view. In the facts that
ground the two minds claims, it looked to
me like there were notions that admit of
degree. So I think it various times there
were phrases like, 'there are two minds
when the hemispheres are mainly or
predominantly independent'. So yeah, on
your view, can the hemispheres be
independent to a greater or lesser
extent, and if so, then can the claim
'there are two minds' be true to a greater
or lesser extent at different times in
different subjects?
Schechter: Yeah, once upon a time
in an earlier draft of my presentation, I
showed a spectrum, Yes, because, of course,
interaction comes in degrees. And if you
picture-- you know, you've some choice as
to what you put it one end of the
spectrum versus the other. If you picture
there being a single dimension, which I think
is in and of itself a little over-simplifying.
But yes, you could picture, say, two non-split subjects at
one end of the spectrum, and maybe one non-split
subject, or one subject who's
undergone a hemispherectomy, removal of
an entire cerebral hemisphere, at the
other end of the spectrum. And then you
have--very rare--but you do have some
intermediate cases. So again, you might
have Brittany and Abigail Hensel, the
conjoined twins that are joined at the
level of the torso, but who are believed
to probably have wholly distinct nervous
systems, except that their behavior is so
coordinated that some doctors don't
believe it. And they're not quite all the
way as far to one end of the spectrum as
two non-split subjects are. Then you have,
say, Krista and Tatiana Hogan, the conjoined
twins that are joined at the level of
the thalamus, and there's some suggestive
evidence that each of them can receive--
that, say, if one of them is looking at
something, the other can see it by
receiving perceptual information through
their shared thalamus. And then, to the
left of that, you see some split-brain
subjects, and then further to the left of
that you see other split-brain subjects.
And I sort of say, you know, these look
close enough to the two mind case that
I'm going to say, you know, that they have
two minds; there's enough inter-hemispheric
independence that it looks like
they're closer to having two minds than
one. And then some of the split-brain
subjects look closer to the one non-split
subject case.
Thomas Nagel: I assume
 you would resist
the radical hypothesis 
that what these cases show
is that a normal, intact human being
has two parallel consciousnesses,
which, however, because of the 
constant exchange of information
with the corpus callosum, have
very similar capacities.
And I wonder, a) whether you think that
that is an intelligible possibility,
and b) why, as I assume 
you would reject it,
and say that the two 
consciousnesses only appear
when communication is stopped.
Schechter: Yeah, thank you.
I view it as intelligible. It could
be--the philosopher mark says, you know,
maybe last year aliens came down and
surreptitiously performed split-brain
surgeries on a bunch of us and we
haven't realized it yet, because we
haven't participated in a split-brain
experiment. You know, if it's the case
that split brain subjects have two
streams of consciousness then it's
possible that I do right now, but surely
I don't.
And so therefore split brain subjects
must have two streams of consciousness
also.
Nagel: I think you've misunderstand me.
I mean ordinary human beings 
who haven't had their corpus callosum split.
Schechter: No, I understand. I was just saying, yeah it's always possible that our consciousnesses are
split, theoretically, and that we haven't
realized it yet, insofar as I don't think
you could realize it from introspection.
When you introspect, any act of
introspection occurs within a particular
stream of consciousness, you won't be
able to introspect conscious experiences
that are occurring in some other stream
of consciousness, so introspection alone
wouldn't reveal it. You know, I think
there would probably be some sort of
behavioral indication even if we hadn't
participated in these split-brain
experiments. That said, even though I
don't regard it as absurd or nonsensical,
the claim that you or I might have two
streams of consciousness as well, I don't
actually think the claim is true. And I'm
relying on, you know, again, the behavioral
differences between split-brain and non-
split-brain subjects. I know you had
mentioned something about cross-matching
and results in non-split subjects. But you know--
I take it, you know, if you look at, again,
like the quantitative results, you
typically don't even have an non-split
control subject when you're doing a
cross-matching experiment with split-
brain subjects, because saying whether
the two stimuli are the same or
different is so trivially easy for non-
split-brain subjects that
they're just at ceiling. This is
something that split-brain subjects are
a chance at. And again, that's the kind of
result that suggests two streams of
consciousness in a split brain and not
in a non-split subject.
Chalmers: What I'm--just to
be clear, why exactly do you say
introspection can't reveal it in this
case. I was thinking, on Tom's idea, if
there's in fact two subjects in here, and
let's say, well each subject is going to
be conscious of half a visual field: a
left visual field and a right visual
field. Now I introspect that I'm in fact
conscious of both the left and right
visual field, therefore I am not either
of those two subjects. Wouldn't
that be introspection?
Schechter: Well, it's not purely
 introspection in that
case, right? I mean I will say--so this is
something that was mentioned before too.
The split-brain subjects
 it's not that they are only
conscious of one half of the visual
field. You need to speak about the kinds
of things they're conscious of. So for
instance, they can tell typically when
something has happened somewhere--like if
a light has flashed somewhere in any
part of the visual field. It's not clear
whether that's a specifically--it's hard
to tell sometimes
that's a specifically visual effect or
some kind of attentional effect or
something like that.
But even if we picture only being
conscious of one half of the visual
field, that wouldn't tell you that there
is somewhere else inside you some other
being that was conscious at the other
part of the visual field. The most you
would know is that you can no longer see
things on the left, or that you can no
longer see things on the right. So there
would be a theoretical inference there
also. Does that make sense?
Chalmers: But if we can know that we in fact
experience things on both halves of the visual field, 
and we know there's at least one being who
can experience both, and, therefore,
that it's not the case that there's merely
one being who can experience the left
and another being who would experience
the right. I take your point that
maybe the other two-subject hypotheses
could persist; maybe there are two
subjects who have exactly the same
conscious experiences inside my head.
Okay, there's no way I could disprove
that. But at least the traditional one,
where each gets sort of half of the
experiences, it seems as strong
introspective experiences.
Schechter: Yeah, so again if
you look at cross-matching experiments,
for instance, where again, distinct
stimuli, or sometimes the same stimuli,
are directed to different hemispheres,
and you're asking the subjects to
indicate whether the stimuli are the
same or different. And let's say the
subjects are at chance: they can't say
whether that's same or different. Okay,
one hypothesis is, they can only see one
visual field--they can only see
information from one visual field at a
time. Or maybe they're totally blind with
respect to one of the visual fields. Of
course, you therefore need other
converging evidence, from other trial
types, to suggest that the subjects, or
that something within the subject, is in
fact conscious of the right visual field
stimulus and the left visual field
stimulus. So I take it again the issue is--
I mean, the subjects will say, you
know, they often say things like, "well, I
didn't see anything on the left".
It's the behavioral evidence that
suggests that in fact seeing of what was
on the left did happen. I'm trying to
think of a neutral way to put the point.
And again, that's what you won't be able
to tell from introspection.
Chalmers: Jackson.
So if I had to choose a side, 
I'd lean towards the two minds.
But I guess I wanted to 
put forward the
challenge that there might not be an answer.
So, you know one thing you might
think is, like, well why do we think there
must be an answer in the first place? Well,
because we have sort of, like, a priori or
pre theoretical commitments about the
structure of phenomenal minds, so
phenomenal minds have to be unified, and so
there's some tension here if we see the
brain as not unified in the right
way, and we think there's a phenomenal
mind there. Another option, though, is to see,
like, you know--so businesses are
organizations, we can have two businesses
that over the course of many years sort
of come together and come apart. We don't
really think there's any deep fact about
when there's one company versus two
companies versus some mishmash. They're
just facts about integration, and those
are the only, really, facts that there
are. And questions about, like, how many
businesses there are, there's no
meaningful answer.
Schechter: Right. Yeah, I mean, as
has already emerged--I don't know if this is
a question for just me specifically or for everyone--
and I think we all share this view: of
course, there's less inter hemispheric
integration after split brain surgery
than there is before, and yet there's
much more inter-hemispheric integration
after split-brain surgery than there is
inter-brain integration between me and
either of the people here, right? So to
some extent--I mean again, a
split-brain subject is not going to be
located towards the extreme end of the
spectrum, between a clear-cut case of two
minds on a clear-cut case of one mind.
You know, again I locate them closer to
one end of the spectrum or the other,
because I think that that helps us--I
think the way we think about mental
states, we assign them to someone or
something. And you kind of can't avoid
that. And the question is again, whether
you're going to assign them to the
animal, or to one of these hemisphere
systems or the other. And I think again,
that, you know, for some split-brain
subjects it's more accurate to assign
them to these two systems. But I admit that--
yeah, I mean, assuming we have a reductive
account of minds or thinkers, there are
going to be these intermediate cases, and
there's kind of not a point in, like,
pounding a fist on the table and saying,
like, absolutely and essentially two--as
opposed to one barely unified mind, for
instance.
Pinto: Yeah, I would also like to comment.
I think my--I have a different
intuition here. So I guess, yeah, from a
third-person perspective, you can just
quantify how much integration there is, and
so on. From a first-person perspective,
for me it's very hard to imagine--now, I
can understand, okay, there's one person,
there's one experiencer, or there's
two experiencers. But what does it
mean, there's, like, one and a half
experiencer. Yeah, I mean maybe
other people don't have this intuitive
problem, but for me it's just
intuitively hard to grasp. So yeah, I
would say there's a dichotomous answer. I
mean, we may not get it, but I do think
there's like a dichotomous
underlying truth. So it's either there's
one experiencer, or two, or
multiple maybe, but, like, a natural number,
basically.
Chalmers: Joe, could there be 1.5?
LeDoux: No. I mean, I think if there's 
more than one, there's two.
[Audience laughter]
Chalmers: It could be 3.
LeDoux: Could be 3.
Schechter: Yeah, I mean, obviously--
Chalmers: Each hemisphere and the whole brain.
LeDoux: Well, we're all kind of multi--you know,
we're not just--[unclear] said we're one self.
But we have so many selves.
Schechter: I mean, I know this is partly said in jest,
but obviously what's at the intermediate
point in the spectrum is not 1.5, because
that makes it seem as though there's,
like, one wholly unified mind, and then
another half a mind. And that's not the
right way of conceptualizing the
spectrum, obviously.
Chalmers: Chris.
Yeah, this is a question 
for professor Pinto.
I very much like the idea 
that there's a notion of--
the subject is an experiencer. But
if you've got that conception, I was a
bit puzzled about the part of your
argument where you talked about divided
attention. So you raise this question,
whether there can be a subject to
an experience, these unintegrated streams of
information. Then you say, well, we've got
the tracking cases, there we
can divide our attention
we understand that very well, it's a 
very familiar phenomenal experience. That's all true,
but in such cases--the unattended
channel, we're still aware of some of the
features, not so many of them.
Whereas you want to have a case where
there's--we want something that's going
to make sense of two streams which
are not co-conscious at all, no awareness
with the respect to the other, yet still, it's
one subject. And you want that
combination for the notion of a subject
as experiencer, and I'm not sure I can
make sense of that. Well, certainly the
tracking experiments with divided attention don't really seem to help me make
sense of it.
Pinto: Okay, okay, so let me let me
reiterate your question to be sure that
I understand correctly. So you're saying,
to you it doesn't doesn't seem to make
intuitive sense that you have one
experiencer who has two streams of, let's
say, attended information, that this
person experiences. Is that correct?
Chris: So there's two streams, within each stream 
there's co-consciousness. There's no co-consciousness
across streams.
Pinto: Yeah, yeah, exactly.
Chris: I think that the tracking
experiments, where you divide your attention, don't 
really seem to give me any leverage in making
sense of the possibility.
Pinto: Alright, yeah. Okay, so yeah, that's a fair point.
I mean of course with multiple object tracking--
 so what I try to argue there is that what
happens there is that you have multiple
foci of attention, and yeah, of course, you
can cross-integrate whenever you want. So
maybe that wasn't totally clear during
my presentation. I didn't mean to say that in
normal subjects you sometimes find that
they cannot match stimuli across
the midline; you never find that. They can
always do that. No, I was just saying
 if you put in one stimulus, either
in the left or the right hemisphere--
left or right visual field, there's
hemispheric specialization going on, so
their capabilities are different. But to
come to your question, so another
example of split-attention was this more
recent paper by Tononi's group, which
was in a 2016 paper about--Ned comments
on that as well, so he definitely knows
it--and the test they had people do there
is, they're driving a simulator, and they're
listening--they have an auditory stream
as well. And you're either listening to
the radio or listening to GPS
instructions. And what they found if they
looked at the fMRI signal is that when
they
listen to the GPS instructions, then the
information seems to be integrated, so
the two networks processing the auditory
and visual information are highly
interconnected. But when you listen to
the radio while driving, there seems to
be no functional connection between
these two. So that would be another
example of basically split attention or
splits information-processing. And, as Ned
pointed out, well, I mean we've all been
in the situation where we're driving
and listening to the radio, but it still
seems like there's one--like you're the
one experiencer there, experiencing
both streams. So, of course, yeah it is
true we can connect the dots, and yeah so,
if it's completely impossible to connect
the dots, yeah that is kind of strange if
there's one experiencer. I agree with
that.
So I'm also thinking of ways when you do
this cross matching test--at least
when I did the experiments, but yeah, okay
now I go against what I said myself, that's
completely anecdotal as well--I did
notice that sometimes the patient
seems to be able to reason his way
towards the right answer. So it just
seems there's no automatic integration,
but if he starts to think, like, okay the
left was vertical, the right was horizontal,
so they're different. I also press
him, like, no, no, don't--just give your
first response. So maybe also in
split-brains you can find that they
can bridge the gap, but yeah, we
should research that more. But yeah, it's
a good point.
Chalmers: Joe.
Joe: Yeah, I just wanted to
throw out one other kind of patient
that's maybe relevant. We did a study
of some patients with unilateral
neglect in the late 1970s; Bruce Volpe
was the lead author on that paper. And
these people have no visual awareness
for the left side of space, kind of like
a blind side vision. But they were able
to match stimuli that they couldn't name
--in other words, you put, like,
one stimulus in the left visual field,
one stimulus in the right visual field,
and they weren't able to name the left
visual field stimulus, but they could do
a between-visual-field match. So they had
matching for non-introspective information.
I'm not quite sure how it all fits into
what we're talking about but it's--
Chalmers: Okay, Marisa.
Marisa: So one comment just about the attention, 
which is that there's many other processes
in which attention doesn't seem to have these
hemispheric limits.
So, I think this data are not so
much about the consciousness or not, but
rather that it seems that in some
phenomena, especially when there's motion,
there seems to be hemispheric
specialization. And then it's been
postulated that the limited resources
live within each hemisphere, right? But
it's not the case for all attention
phenomena, like far from that. And the
same authors that have published these
have found no differences in many other
instances. But my question was actually
about perception action dissociations,
because I'm surprised actually that it
hasn't been brought up, and neurotypical
observers have perception action
dissociations, right? So if you take to the
extreme that something has been
experienced perceptually and then that
something else is acted upon as
evidence for two minds, then all neurotypical
observers would have two--we would
have to infer that all of us have two
mind. So I wonder how, I think in
particular you interpret these,
Elizabeth--how you interpret these
studies of perception action
dissociations within neurotypical
observers.
Schechter: Sorry, I'm not sure I 
understand the dissociations.
Marisa: So
dissociation is that you perceive
something, and your eyes may be doing
something else in your action, or your
hands may be doing something else. So
there's a very long line of evidence
in terms of dissociations with
reaching between people that say not to
experience something, or experience
something. So, for example, my visual
system is more prone to the middle-line
illusion, but if I have to touch
something or grasp, I may do it the right
way. We have shown also a lot of
perception action dissociations even
within the eye, so I may not be aware of
perceiving something in terms of my
perceptual report, even when it's not just a
yes/no detection test of all criteria
issues, you have like four choice
discrimination tasks, and you're really at
chance, and yet your eyes seem to have
access to the information, so I would like to--
Schechter: Okay, great, yeah. 
That's a great question. So, yeah,
I mean, of course--yes, exactly. So
there are all kinds of dissociations
that we see even within non-split
subjects. In fact, you know, I mean, people
would--no one would say now, like, oh the
human mind is highly unified or highly
integrated, right? We've sort of moved to
the other end of the spectrum, where
people talk about you know how 
disunified the human mind is in various
respects, and how much kind of, you know,
semi-autonomous processing at different
streams of information there are
within the brain. I actually
don't think that the--I don't think that--
so when you think about the split-brain
cases, you need to think about two things:
you need to think about how things are
dissociated, and what's dissociated. And I
don't think that the--you know, how things
are dissociated from each other is
actually necessarily very different in
the split-brain case. The question is, what's
dissociated from each other? So for
instance, the kinds of generalizations
you're talking about, where, you know,
again, there's, like, when you actually
reach for the circle that's surrounded
by the bigger circles, versus by the
smaller circles, your grip aperture is
correct, even though you, you know,
consciously report these things as being
of different sizes. You know, you find
that same kind of dissociation within
each hemisphere system also. So we need
to look at kind of--I mean, it is
interesting, because you could ask sort
of, how startling this is, and to what
extent this kind of generalization
problematizes our understanding of the
identity conditions of perceiving, or of
reaching. But I'm assuming it doesn't
problematize it that much. The kinds of
dissociations you see between, you
know, vision for action versus vision for
identification systems. And so, what we
see in split-brain subjects is that
different kinds of things are
dissociated from each other than are
dissociated, again, between the vision for
action system and the vision for
identification system. So again, you look
at the comparisons partly between non-
split and split-brain subjects, and it's
those comparisons--again, the things that
you don't find dissociated in a non-split
subject--that drive the two thinkers mind,
and ultimately help justify the two
thinkers claim.
Marisa: I thought you were talking
about the interaction when you were
making your argument, that's why I was
just taking it to the extreme, and saying,
wouldn't one have to then infer, in cases
of neurotypical observers, when you see
these very pronounced perception action
dissociations.
Schechter: It depends on what you
should expect to interact, right? So if
you don't see in non-split
subjects this kind of interaction, again,
between representations in the vision
for action system and in the vision for
identification system, then you know
that's normal, right? And so, that doesn't
drive the two thinkers claim. It's
instead things that normally are
integrated, that normally do
interact, in the non-split subject but
sort of guide our understanding of what
it is for something to be, for instance,
consciously versus non-consciously
perceived. When you don't see
interactions, you know, of that sort
that's what, again, helps justify the two
thinkers claim. Does that make sense?
Chalmers: Do either of Yair or Joe 
want to come in on this?
Pinto: Joe, you can go first 
if you want to.
Chalmers: I was just thinking 
if either of you wanted to come in on this.
LeDoux: No.
Chalmers: If not that's fine.
Pinto: Yeah, I mean--just maybe a short comment. 
But yeah, of course you're right--there's a lot
of--well, I would repeat what Lizzie says:
there's lots of disintegrated
information processing in normal people
as well. But I agree with Lizzie: if you
find certain things that are never
disunified in healthy adults which are
disunified, and seem to really touch upon,
you know, the subjective level--because
this seems more like--indeed, I mean, I
think you're referring also to your
Pysch Science paper, of course, which was really
interesting, where
if binocular rivalry--if plates going
like this or both gratings like this
and like this, and people either say that
they see [unclear] go like
this or like this, but their eyes go on a
diagonal. They're not aware of that.
But this could also just be some kind of--
 I think it that is just some
kind of, like, unconscious inform--yeah
unconscious processing, and I think what
Lizzie and Joe are referring to, which are
the more exciting cases, where there
really seems to be some kind of
conscious processing that's disunified.
Schechter: Yeah, I didn't mention consciousness in
my answer, but I think you're right that,
you know--I mean especially now that we
recognize how disunified the
neurotypical mind is in various respects,
it's kind of like, if there's conscious
unity, that's what unity there is in the
non-split mind. And then that places
greater weight on--someone had asked
before this question about the
distinction between unity of mind versus
unity of consciousness--it does place
additional weight on the issue of
whether consciousness is unified or
divided after split-brain surgery.
Chalmers: I still want to get a little bit
clearer on the disagreement among the
three of you, and to what extent it's
empirical and to what extent it's more
theoretical or philosophical. I mean, clearly there
is some empirical disagreement about these
split-brain subjects: Yair thinks that,
okay, the subject he's examined show this
inability to compare across the
hemispheres, but they don't show this
ability to give different responses
depending on whether it's, say, the left
half or the right half of the body, and
is inclined to question whether that--how
widespread that phenomenon is in other
subjects. So I guess that we can do this
in terms of, like, a conditional question.
Just say it turns out that all the
subjects go Yair's way. And, you know,
they're not very good at comparing
across the hemispheres, but they can, in
fact--they do more or less give these
uniform responses for the different
halves of the body. Would everyone then
be prepared to accept that those
subjects have just one mind not two?
And then likewise for the other kind of
subject, for the ones that go, let's
say Joe's way or Lizzie's way, with very
non-integrative responses between the
two different sides of the body. Would
everyone be inclined to accept that
those subjects have two minds rather
than one?
Pinto: Yeah, so, I would definitely be willing
to accept that. So, indeed, as I already said,
if we do this visual imagery
experiment and it turns out that each
hemisphere basically gives its own
answers, yeah we throw in the towel. I
would say, okay, then. That for me is
conclusive evidence that there's two
people in there, and somehow the unity
happens at later stages--maybe through
cross-cueing or subcortical or whatever.
So I would say yeah, if it all--if all
the empirical data goes that way,
for me case will be closed.
Chalmers: And even for behavior?
Pinto: Yeah, behavior even more. But, I mean,
there I'm pretty convinced we won't find
it, because I already did these kind of
tests. But yeah, for behavior even more. If
you indeed find the equivalence, in a lab
setting, of the left hand fighting the
right hand, yeah, I mean, how can you
still argue for one person?
Chalmers: Joe.
LeDoux: Well I would say that we'd
have to do it on the right patients, that
patients that are several decades in
are probably not the true test. I mean, if
there were brand new patients, we could
do these more quantitative assessments,
and maybe answer it. But I think it's
gonna be hard in these patients that
have been operated on so long ago.
I mean, there'll always be some question
about it, I think. Just because of the
possibility of reorganization, and, 
as Lizzie described, things that have changed
over the decades that even in those
patients we were studying then.
Chalmers: So that's to say you think that 
now Yair's patients might have one mind,
but just say it turns out that all split-brain
patients only always look like Yair's
patients. Then they always have
one mind?
LeDoux: Yeah, I guess. You know, 
I would have  to know more about it,
but I think yes if that were true.
Schechter: So the striking result
of Yair and colleagues is that--you know,
they obtained the traditional findings
with respect to cross-matching. With
respect to crossed responses--so responses
of the left hand after right hemifield
visual presentation, or using the right
hand after left hemifield
presentation, or speech after left
hemifield presentation. You know, he's right
that if you look at the textbook
presentations of the split-brain
phenomenon, what they always mention is
this incapacity for crossed responses of that
kind. And instead he finds this
preserved capacity, sometimes very good,
for crossed responses. I want to know--
I mean, to me the question is how that's
happening. So, you know, is it happening
because there's integration of
intention, so that--I think
you agree with this--so that
there's actually sort of only one
decision-maker within the split-brain
subject.
Okay, now that starts to look like a
unified agent, again, who has some
fragmented information coming into the
agent. On the other hand again, if the
integration is--well, if it's either of,
like, a very low level motoric
integration, or possibly not integration
at all,
but just again, like, outputs of cognition
and perception and decision-maker that
are converging on the same set of
effectors, then that to me still looks
like two agents and two thinkers. So I
really want to know, again, like how these
behaviors are being produced.
Pinto: I completely agree with that, 
by the way.  That's a good point.
LeDoux: So, I mean,
let's go back to the the issue of
language, and what that does to the two
hemispheres. I mean, I know there's some
right hemisphere language in all of
us to some extent. But the dominant
operation of language is in our left
hemisphere. And if you've isolated
that, you're gonna have a system that has
a kind of much more verbal working
memory operation than you have in the
right hemisphere, where it's gonna be
maybe some verbal but primarily
nonverbal. and we always thought of the
right hemisphere as kind of like a smart
chimpanzee, rather than a full-fledged human with
self-awareness and so forth. And
putting language over there seemed to
kind of add a little bit of extra stuff.
So I think that that's just important to
keep in mind.
Chalmers: Okay, let's try and get one
or two more in quickly--let me just
check. Okay, Paulo.
Okay, let's go to Paulo
quickly. See if we can get 3 in.
Paulo: So my question
 concerns emotion as a relevant
condition for the attribution of
consciousness and possibly mind. So how
do you think the interpretation of this
data in terms of one or two minds or
consciousnesses can relate to our
knowledge concerning the neural
correlates of emotion, versus cognitive
capacities.
Chalmers: I say that's a question for Joe.
LeDoux: That's a long discussion. I mean, you
know that gets into what my view of
emotion is, which is that it's a cognitively
constructed interpretation of ourselves
in a social situation, and not a
hardwired response bubbling up from, say,
the amygdala. I mean I've worked on the
amygdala for a long time and over the
years--I mean, my view has always been
that emotion itself--fear itself, for
example--is a cortical, working-memory
kind of operation, with a lot of
different kinds of inputs than you would
have in a non-emotional
situation. And that the--what the amygdala
and other sub cortical circuits do is
control our behavioral and physiological
responses. And those things happen in
parallel, but consciously we interpret
those body and brain responses as part
of our emotion schema that puts it all
together. That's a very short summary and
it's probably not very clear but did
that help?
Chalmers: Andrew.
Andrew: I had a question for Yair and Liz. I
guess I'm still not sure exactly what
the fundamental disagreement is between
you two, and I'm wondering if you two
might just be concerned or investigating
different phenomena. And I'm wondering
this because Yair has kept emphasizing
that he's concerned with conscious
subjects, and that's the central issue
that's at hand for him. And Liz keeps
saying that she's concerned with minds,
where mines are understood in terms
of, like, mental capacities that are
individuated functionally, and are
integrated with each other. And, you know,
it seems like you could think that in
split-brain patients, they might have two
minds in Liz's sense but still just one
consciousness in Yair's sense. So I
guess I wonder whether you two are
disagreeing on that, or whether your
views that you've been advocating for
here are reconcilable.
Schechter: I think I might be
more responsible for uncertainty on this
point than Yair is, so let me speak first. I do believe--I argue in the book also--
two streams of consciousness, two
intentional agents. I view the two
minds claim as more radical, but it kind
of encompasses these other claims, or
it's at least, like, a broader claim than
the two consciousness or two agents
claim. I mean, I'm sure that some of our
disagreements--it can't just be empirical.
Some of it has to be theoretical
somewhere. But, you know, if I think
I've understood the argument of the
paper, I accept the--again, we have a kind
of empirical disagreement about what
kind of integration is happening between
right hemisphere and left hemisphere
mental states--but I accept the basic
form of the argument that if there's one
intentional agent after split-brain
surgery, then there's one stream of
consciousness. And I would say vice versa
as well, because--this just goes with my
theory of consciousness--I don't see how
you can have one stream of consciousness
if you have two distinct agents or two
streams of consciousness if you have one
agent. So I think that we actually agree there.
Pinto: Yeah, so in that sense, yeah--although my
claim is primarily unconscious subject,
but how are you going to measure that? So
then I would indeed say--I will be very
surprised if there's one conscious
subject with two independent minds.
So if indeed if you find evidence,
you know, through resting state
connectivity or whatever, there's two
independent streams of conscious
thoughts, and their each hemisphere has its 
own preferences and so on--yeah, if you want
wanna be really philosophically radical, you
can say, well, it's one conscious subject
with two minds. But then I would say
no, that these are two conscious
subjects. So I would also say that at a
higher level there has to be also one mind,
I guess.
Chalmers: Okay final question from Zoe.
Zoe: Thanks so much. I'd really love for you 
guys to tell us more, or speculate or hypothesize
if you need to, about how the two hemispheric 
systems, be they deserving of the term 'mind'
or not, are able to coordinate to the point 
of taking turns, as in the case that professor
Schechter described, in which the subject
draws a sky and then draws a scraper.
So I'm thinking it's so strange to imagine
a hemispheric system who sees the word
'scraper', and is told to draw what it sees,
and is kind of waiting patiently while
the hand it's presumably trying to control
draws a sky, and then [inaudible] like, oh good,
now you've regained control of the hand, I can
draw my scraper. At the same time it's
equally strange to imagine that there is
some degree of interaction. That the two
hemispheric spaces are saying to one another, 
oh you go first. [inaudible] So what's going on?
LeDoux: Well, it's like, you know, if you have a
really bossy person next to you that's
talking all the time and doing all kinds
of stuff, you kind of lose interest in
gaining control.
[Audience laughs]
Schechter: Yeah, that's a funny question.
and I admit I hadn't thought about that
before. So I mean I do want to note,
you don't always get patiently waiting
for a response, right? You get cases in
which the behavior looks a little more
disunified, and presumably that is
because in those cases there's
sort of conflict: someone starts drawing
something, and then it's like, "what? That's
not right, how is that an ice scraper?" and
sort of crosses crosses it
out, or just starts to draw something else.
On the other hand, again, I mean, I think
this gets back to kind of the question
that Dave started with, of, like, if there
are these two thinkers there, how do they
not realize the other's presence. You
need to picture a certain amount of kind
of--a certain patience or 'go with the flow'
type attitude on the part of each of
these thinkers. And I think that you
could explain that partly in terms of
the fact that these are experienced
subjects. You get--from what I understand,
they will be more freaked out in some of
the earlier experiments when they find
themselves correctly answering questions
that Lefty, at least, has just claimed it
doesn't know the answer to and so on. But
with, you know, most of the subjects--and
there are personality differences here--they
just come to--you know what I've read is
that they've just come to accept that
they might not feel that they know the
answer to a question, but they're
supposed to guess anyway, or they're
supposed to allow the behavior to emerge.
And then they find that they've done
better than they anticipate, or again, the
subject has done better than Lefty has
anticipated, and so on. I think something
like that might be operating there.
Again, that they're kind of, not trying to
control the behavior necessarily as
much as you or I would, if we suddenly
participated in this experiment.
Pinto: Yeah, I guess I would
have a much more mundane explanation. 
In my view it's it's just one person
who cannot connect the dots, basically. So
to be, like, okay, how's that possible? Well, it
just doesn't get automatically connected.
So the example I keep using until I come
up with a better one is, like, as I said
before, an out of sync movie. So you hear
voice, you cannot connect it to which
actor it comes from. For somebody who
watches an in sync movie this seems weird.
Like, okay, don't you realize that this
person is saying it. But yeah, for them this
doesn't happen automatically, so for them
it's just natural to draw a sky and 
a scraper, because it's not integrated
automatically. That would be my
explanation of the data point.
Chalmers: Okay, so there's now going to be food
for us in a reception outside, to which
everyone is welcome. Let us thank our
debaters for a great debate!
[Audience applauds]
