The following content is
provided under a Creative
Commons license.
Your support will help MIT
OpenCourseWare continue to
offer high quality educational
resources for free.
To make a donation or view
additional materials from
hundreds of MIT courses, visit
MIT OpenCourseWare at
ocw.mit.edu.
PROFESSOR: Last time, we talked
about attention and the
idea that attention has
got some properties.
We're very limited in what
we can focus on.
We attend to less than
we might guess in our
environment.
On the other hand, there are
channels of information that
sneak into us unconsciously
or with minimal attention.
And experimental research has
shown us what requires our
focused attention to be noticed
and what can sneak in
through pathways, things like
features in our environment.
And so I want to talk to you
today about two kinds of
spectacular disorders of
attention in a higher level
vision and insight they
give us into the
brain basis of attention.
And again, the message is how
much we construct by the rules
of our mind and brain
the environment that
we see around us.
So we'll talk about
blindsight.
That's a great name, the
paradoxical state that people
are cortically blind, but they
kind of perceive some things.
So we'll talk about that.
What is it?
What do we know about
its brain basis?
What system of unconscious
perception
might be in our brains?
In these patients, it's their
only visual system.
In you and I, it's something
in us, and we don't know
exactly what it's doing relative
to our conscious
visual system.
But we have the same brain
system available to us.
And then neglect, what it is,
its brain basis, and how it
teaches us again how we
construct the world around us
to know what space we're in
and what's around us.
So a reminder, and I think you
know this well by now that the
world out there is divided into
a left and right visual
field as we look for it in the
middle, that the information
from the left visual field goes
through your brain and
ends up shown in the right
primary visual cortex, from
the right visual field
into your left
primary visual cortex.
But there's one other pathway
we haven't talked about very
much which goes to a structure
called the superior
colliculus.
It's part of your midbrain.
And it's the system we think
gives rise to the possibility
of sensation without
perception.
That phrase, sensation without
perception, is a good one to
describe blindsight.
And we'll describe
it in a moment.
So from your retina, where all
vision has to go through, a
little bit of information--
a small number of fibers-- go
to part of your brain that
controls your pupillary
reflexes, what makes your
pupils get wider or
smaller to see.
90% of the fibers coming in, the
fibers come from your eye
and go through the lateral
geniculate or through the
major system that you've heard
about from Melissa that
connect to your primary
visual cortex.
And then, there's one other
small visual pathway from your
retina to this superior
colliculus sometimes called a
tectopulvinar system.
So it's a small pathway from
your eyes in terms of the
number of nerve fibers.
And so people said, well, can we
say what's not done by the
major visual pathway that goes
from the eye to the cortex?
What's done by this other
small pathway?
And one of the ways they looked
at it originally all
the way back in 1881 was to
create in dogs bilateral
occipital lesions.
So now, they're cortically
blind.
They're not retinally blind.
They're cortically blind.
It's in the cortex.
And what could these
animals do?
And they were very impressed.
Although these animals didn't
recognize many things, they
could steer their way around
their environment.
They wouldn't bump
into things.
If you had a blindfold on or
if you were retinally blind
and weren't given any
opportunity to know your
environment, you would bump
into things, right?
But these animals seemed to
steer their way around things
pretty well.
And they can do some other very
simple tasks even though
they ought to have been
seeing nothing.
So this is a suggestion in
animals that there's something
in the brains of primates that
gives you some information
that doesn't go through
your conscious cortex.
And then, a number of patient
studies in patients with
naturally occurring injuries
have really shown us, given us
a chance to experiment on them
in a human and relate them to
human experience.
So here's a patient who had a
large injury, a large bleed,
in the right visual cortex.
So because of this, this
patient, this man was blind in
the left visual field.
This field was fine.
This field was blind.
Cortically blind.
And the way that people figure
out in what way are you blind,
what parts of the world do you
see and do you not see, is
they'll put you in front
of a computer monitor.
And they'll turn on lights
in various locations.
And they'll create a map like
this, which shows you where
you respond when a light comes
on and where you don't see it.
So your job, basically you
just look in the middle.
And you say, push a button
when a light comes on.
So you're waiting.
And a light comes on somewhere
on the monitor.
So what this picture is showing
you is that the person
could respond when the lights
came on anywhere on the left
side, but never responded, never
said a light came on on
the right side.
People call this perimetry.
It's a standard neurological
test of visual difficulty.
Here's a person whose injury
harms only a quadrant of their
visual field.
So they never respond when a
light turns on in that quarter
of the world out there.
But the other three quarters,
they respond to.
So that's a way of testing
what do you do.
And you're not asking them
anything sophisticated, just
did a light come on.
Is that OK?
So for this patient,
here's the mapping.
This patient was fine in
the right visual field.
This is one eye.
This is the other eye.
And terrible--
with a few spots a little bit
better-- because lesions
occurring naturally in people
are seldom perfect lesions.
But you can see that all this
area that's dark are areas
that, when a light came on in
the left visual field, this
man never responded that
anything had turned on.
There's nothing simpler,
right, than a light
turning on and off.
He did not experience anything
turning on in that way in the
left half of the world.
So they noticed as they gave
this test that even though he
was saying, I don't see
anything, nothing's happening,
that when they flash something
in that cortically blind
field, he would move his eyes
in that direction as if
something in his mind
and brain felt
something had happened.
Not only something happened, but
roughly where it happened.
But that information was
not available to
his conscious mind.
He's never pushing a button
that he says he saw it.
He always says nothing.
I'm waiting for something
to come on.
And if it comes on in his
good field, he responds.
Does that make sense, OK?
But something seemed to do it.
And when they found that it was
better than chance in the
left visual field, about things
like if they put on a
bigger patch of light.
He could tell if they gave him
a short line or a long line.
Now, he would never say,
I see the line.
You would have to make
him make a guess.
So when you read the papers,
it's something like, I don't
see anything.
I don't see anything.
Well, you must guess.
Is it a short line
or a long line?
I don't see it.
There's no basis for
me to guess.
It'll be a completely
random guess.
But you must guess, OK?
Short or long?
And then, if the lines are far
enough apart in size, he's
almost 100%--
97% accurate.
If he's forced to guess but he
never has the experience that
he sees the line, he's just
forced to guess and told that
it's two lines.
Or he can judge things like,
is it a circle or a cross?
Is it an x or an o?
But he can't do something like
a square versus a rectangle.
It's very limited.
Subjectively, he always
feels he sees nothing.
If he's given two choices, for
some things he can make the
correct choice if he's forced
to make a guess.
And there's other sophisticated
ways, again, to
show that even though he's
unconscious of anything in his
blind field, something in his
mind and brain is processing
information there.
So here, they had a thing where
he pushed a button when
a light came on.
This is his good field.
And it takes him, on average,
359 milliseconds.
Now, they do the same thing.
This is his good field.
But they put on at the
same time a light
in his blind field.
And when they do that, his time
goes up by about a tenth
of a second as if the
distraction in the blind field
was slightly distracting him
from making that button press.
So another objective way of
demonstrating that some
information has been processed
in the blind field even though
he never says he feels like
something's happening there.
So here's one more patient, and
the last one I'll show you
of this kind, who had the
unfortunate occurrence of
having two strokes, one in the
left occipital cortex and one
in the right occipital cortex,
about 36 days apart.
So now, he was blind in both
fields by the time he had had
both of his strokes.
So he was a very
unlucky person.
Here in the dark is
the missing cortex
that has died away.
Now, always the problems with
humans is the injuries are not
controlled and precise.
And so here's two examples, one
in monkeys, an incredibly
clever experiment to get a
monkey to tell you what he or
she is thinking about.
And then, one with infants
as well, human infants.
And how do you get a monkey
to talk to you about their
subjective experience?
The striking thing about
blindside is the person's
saying, I see nothing.
I see nothing.
I see nothing, even as he walks
past obstacles with
precision and carefulness.
So here, what it is, they took
monkeys and made unilateral
lesions in them.
There's a control monkey and
three where they surgically
removed, as precisely as they
could, the left occipital
visual cortex and the corpus
callosum that connects the
left and the right.
And the first task-- and I'll
show you in a moment-- was to
touch a light when
it comes on.
And the second half is the
clever design to get the
monkey to tell you what
he or she subjectively
feels is going on.
So here's the video they would
make of the monkey.
And in one case, here's
the light coming on.
So the monkeys had
left removal.
So this is the blind side.
These bars show you how often
they point correctly to a
light going on.
And under this circumstance,
forced to point, forced to
point, here's the
control animal.
And you can see that the animals
who are blind in this
field do almost perfectly.
When they're forced to point,
they pick almost perfectly
which stimulus comes on
in the blind field.
Now, they add one more thing
to the experiment.
They have a number of lights
on the good side.
Here is a response that they
can push to signal "I saw
nothing." And if they truly
saw nothing, they get the
juice reward for which
they're working for.
But there's a light that can
come on here in their bad
field on their right side.
Now, what happens?
Here's the control monkey doing
perfectly well for the
lights on this side, lights on
this side, and when nothing is
happening pushing this
bar to signal
that nothing is happening.
Sometimes, no light comes on.
So now, the monkeys will have
to say, "I see nothing," by
pushing this big panel up
here if nothing seems
to have turned on.
But look what happens to the
monkeys with the cortical
lesions on the left.
When this light comes on, they
almost never say they saw it.
They almost always push,
"I saw nothing."
When they're allowed to say "I
saw nothing" by the response,
then even though this thing that
you know they can see--
because you see here
they're responding
perfectly well over here--
but when allowed to consciously
respond what they
see, then these black bars
are all the way down.
They almost never indicate
they saw something.
They almost always pick the
response, "I saw nothing." So
the monkey is telling you what
his subjective experience is,
which is like the humans with
the cortical lesions.
They're reporting they see
nothing, even though some part
of their brain can pick it up.
How about in humans?
So sometimes humans, children,
infants, for medical reasons
have to have hemispherectomies
in the first year.
These are unfortunate infants
who have severe brain
injuries, severe epilepsy.
And it's considered better to
help them by removing an
entire hemisphere than to let
them have the severity of the
epilepsy they were having.
These are rare cases in very
unfortunate infants.
And in these infants who got
this for purely medical
reasons to make their lives
better, they also did an
experiment to show you something
not only about, I
think, again, what happens in
our conscious visual system,
but also how that system grows
in infancy and the growth of a
conscious cortical
visual system.
So here's what they did.
Infants this young-- because
they're in their first year--
can't even point and you can't
tell them to point.
So again, you have to be
clever experimentally.
And what they did is they
watched where their eyes moved
and recorded that information.
And that was the behavior.
Sometimes, they would
have a fixation.
They've always had a fixation.
You're looking in the middle.
And then, something would come
on out of side or this side,
in the blind field or
in the intact field.
And they would see how often
would their eyes move to a
stimulus in their good
field, which they
expected all the time.
But how often would it move to
the stimulus in the blind
field, the eye movement?
Then, they had a competition
condition where you have a dot
in the middle.
And that fixation dot would stay
on while a box appeared
here or here.
So the only sense--
the only difference between
these two is there's a dot in
the middle that can compete
for what you look at.
OK?
It's not a big competition.
It's just a boring dot
that stays on.
But there's a big consequence.
So here's how often they moved
their eyes to the target in
the non-competition condition.
The dot goes on.
It goes off.
And the box comes on in your
good field or your bad field.
And all these bars are
up at the top.
And practically every trial, at
eight weeks, 10 weeks, and
12 weeks of age, the infant
moves his or her eyes to the
stimulus whether it's in the
blind field or the good field.
So something in their mind and
brain is letting them identify
something and moves their eyes
to the good field, much like
we talked about before
for the adults.
Now, in the competition
condition, you can already see
it's not quite the same.
If there's a dot on and the
box comes on their blind
field, they don't always
make it to the box.
That dot is capturing their
conscious cortical attention
and diminishing the likelihood
they notice the box coming on
in the blind field.
And as the weeks pass from
eight to 10 to 12, just a
month of development,
look what happens.
This bar goes from a little
lower, a lot lower, near zero.
That is, from eight to 12 weeks,
what it looks like is
happening is that as the
cortical system matures and
the infant's consciousness is
growing in some sense, now
it's no longer tending to
process the information in the
blind field if there's
competition.
Because the growth of that
consciousness in the cortex is
suppressing the ability of the
infant to communicate with
unconscious systems or be guided
by unconscious systems
in the brain.
So the cool thing is the
implication of this, is all of
us have this collicular
system in us.
It's a visual system
that's been around
long through evolution.
All of us have this massive
conscious geniculate, the one
that goes into your
cortex system.
And that dominates this
other system.
And so we only see it
revealed in these
patients as guiding behavior.
But who knows what it
really does in us?
Because it's quietly
sitting there.
We don't have conscious
access to it.
And who knows how much it's
guiding our behavior?
And it's very hard to
figure that out.
But it's definitely disappearing
from our
conscious life within the first
couple months of our
development.
So now, I'm going to switch to
the second major disorder
we'll talk about, attention and
neglect, and go through
anosagnosia, a spectacular
version of that disorder,
something about how it's
behaviorally measured, its
brain basis, and then
a few more analyses.
But in the book, there's
a very nice
chapter about these patients.
Now, patients with blindsight
are extremely rare.
You have to have exactly the
right kind of injury to damage
a lot of your occipital
cortex.
And those kinds of injuries
rarely occur on that scale.
Attention and neglect, what I'm
about to describe to you,
if any of you become physicians
or work in hospital
settings, you are guaranteed
to see this a lot.
A lot-- it's very, very common
for patients who've had things
like stroke or brain injuries
of some kind or another.
And a pretty typical example
is from Oliver Sacks.
Most of the Sacks cases are
pretty rare, prosopagnosia,
pretty rare.
Neglect?
Incredibly common in
the hospital ward,
in neurology service.
So here, he talks about a woman,
an intelligent woman in
her 60s, massive stroke
affecting deep or inner back
portions of her right cerebral
hemisphere, good
intelligence and humor.
And what happens to her when
they bring her her dessert or
coffee on her tray
in the hospital?
PROFESSOR: Yeah, she complains
that she's not getting enough
food because she's only
eating food on the
right half of her plate.
The left half of the plate,
it's as if it
weren't present for her.
When they say, "But Mrs. S.,
it is right there on the
left," she seems not to
understand what they say and
does not look to the left.
If her head is gently turned
so the dessert comes into
sight in the preserved right
half of her field, she says,
"Oh, there it is!
It wasn't there before."
You understand?
It's as if the left half of
the plate did not exist.
And if they swivel her head and
now that left half of her
plate is in her right field,
now she goes, oh my gosh!
Who snuck that on my plate?
Now I can finish my meal.
And it's not just that.
She also only puts on makeup
on half her face looking in
the mirror, which can lead
to comical impressions.
So she ignores the left
half of her world.
And it's not just that
it isn't there.
It's as if it couldn't
be there.
It's as if, what are you talking
about there's a left
half of something?
I see everything.
So we'll talk a little about
this and understand more
of it coming up.
So neglect means a failure to
respond or report to something
that's opposite to the lesion--
contralateral means
opposite to the lesion--
that can't be accounted
for by simple things.
These patients don't have
primary visual problems.
They understand language.
They're paying attention.
They're the ones who deny the
left half of their body.
They dress on one side.
They eat from one side
of the plate.
And they also have something
that I'll show you in a
moment, the example because it
comes back a couple times.
And it sounds fancy,
but it's simple.
There's extinction to double
simultaneous stimulation seen
in the late stages.
So here's what the neurologist
does-- and you'll see at least
one neurologist doing this in
a film clip coming up-- and
they do this all the time
in the hospital.
They'll wiggle their fingers.
They'll try to get it in the
middle of the patient.
This isn't carefully controlled,
but it's done on
the bedside.
They'll wiggle one side
and say, do you
see anything moving?
Or the other side, and sometimes
they wiggle both.
And the typical response
in neglect is already
fascinating.
So past the early stages of the
disorder, they'll notice
the thing on the left side.
From their perspective, that's
their neglected side.
They'll notice it on
the right side.
That's their good side.
They're noticing this
finger wiggling.
They're noticing that
finger wiggling.
But when the physician wiggles
both fingers at the same time,
then the patient will
only notice the
one on the good side.
It's as if this is extinguished
because this one
grabs your attention.
And you know they can
see it by itself.
So it's only when it's both
sides that it's extinguished.
And we'll come back to that.
It's interesting.
It's not that their
mind can't see.
But when there's competition
in the two fields-- which
reminds me a little bit
of blindsight --
then their mind can't see it.
So a strong, a fascinating and
rarer piece of this, but again
not very rare, is something
called anosagnosia where they
not only have the neglect that
I just described, but they
deny any problem at all.
So typically, the patient has a
big, right lesions, about 5%
of neglect cases.
And a very fascinating
neuroscientist, you may have
read some of his stuff.
He's a very creative mind,
Ramachandran at UCSD, did some
semi-experiments with some
of these patients.
So these are patients with
right sided lesions.
It says they have weakness or
non-use of their left hand.
And so here's his dialogue
with them.
Can you use your right hand?
And that patient's
hand is fine.
Yes.
Can use your left hand?
Yes.
The patient can't use
her left hand.
Are your hands equally strong?
Yes.
Can you point to my nose
with your right hand?
And she does.
Her right hand is fine.
Can you point to my nose
with your left hand?
The paralyzed left hand-- it's
the left hand because it's a
right hemisphere stroke--
does not move at all.
Are you pointing to my nose?
Yes.
Can clearly see it pointing?
Yes, it's about two inches
from your nose.
Can you clap?
Of course I can clap.
And here's what she does.
Are you clapping?
Yes, I'm clapping.
She can't move her left side.
But in every way in this
patient's reports, she seems
to deny in a deep sense that
there's any problem in her
performance or any weakness
of any kind.
So he wanted to do a couple
little experiments to show
that it's not just that they're
saying, but they'll
follow all the way through.
So imagine that you had
injured your left
arm, was in a cast.
And somebody asked you, I'm
going to give you two choices.
I'm going to give you $5 to
screw in a light bulb--
your left arm is
in a cast now--
or $10 to tie your shoe laces.
Which would you take?
The light bulb, right?
Because it's going to be hard
to tie your shoe laces with
one arm out of action.
This person is the same way.
She's had a stroke.
Her left arm's not
functioning.
She should definitely
take the light bulb.
She takes the shoe laces.
When the physician,
Ramachandran, describes as she
sits there with one hand trying
to flop the laces
together making no progress at
all, he says finally he has to
end the exercise.
He can't take it anymore.
She'll just keep going until--
So she just doesn't process
that her left side of her
body's not working.
And then, he does another
experiment more impressive.
I can use one of
these, I think.
So imagine this was a tray of
cocktail glasses full of
water, let's say to
the very brim.
Imagine there's three here
and three-- six things.
You can see they're
right at the top.
And you're just hoping that the
person bringing it to you
doesn't spill it on you.
And the person brings it over
to you, actually filled with
water and asks a patient
to hold the tray.
OK, can I pick on you
for one second?
Imagine you had only--
how would you hold the
tray if one arm was
unavailable for you?
OK, I'm bringing this over.
You have to watch,
very exciting.
There's water.
Yes, OK.
How would you had if two hands
were available to you?
OK, thank you.
OK, right?
That's easy for you to imagine
how you would hold it.
They walk over to the patient
with all this stuff.
They hand it to her.
And what does the patient do?
She puts out her right hand
on the right side.
And the whole thing
falls over.
They're trying to demonstrate
it goes all the way through.
This person really believes
there's not a problem.
And they can be doused in water
for a moment-- and I'm
sure dried appropriately--
and still deny there's
any problem at all.
Now, one thing they can do--
and this is a weird line of
research, but there's a number
of papers that show this.
And I'm not recommending you
do this at home because
actually, it's worse
than it sounds.
They take a syringe with cold
water, and they put it into
the left ear, the
image is here.
The patient's eye
starts to move.
They get a nystagmus.
And they ask them
how they feel.
And then she says, my
ear is very cold.
But other than that, I'm fine.
But they've given her
a little bit of a
shock in the left ear.
And now, he does the interesting
experiment.
Do you feel OK?
She says her ear is cold.
Can you use your hands?
At this moment when they've done
something in the left ear
that wakes up the opposite
right hemisphere.
I can use my right arm,
but not my left arm.
I want to move it, but
it doesn't move.
This happens just in a
moment from the cold
syringe in her ear.
Whose arm is this? holding
up the paralyzed arm.
It's mine, of course.
Can you use it?
No, it's paralyzed-- like, what
kind of doctor do I have?
It's paralyzed, of course.
Now, here's something
really fun in a
Sherlock Holmesian sense.
How long has your arm
been paralyzed?
Did it start just now?
Because what he's asking is,
does she have a memory
somewhere in her mind of her
entire experience, or does she
say it just started right now?
I don't know how
this happened.
It's just not working.
And she says, it's been
paralyzed for
several days now.
About 90 minutes later when they
redo this, she's back to
just how she was.
So they can temporarily
alleviate this by this
irrigation to the ear.
So this denial of the left half
of your body, this denial
that you have any disorder
whatsoever is a
very striking thing.
In most patients,
it clears up.
You saw pictures of
it from Melissa.
You saw movies of patients
with object disorders.
Those don't clear up.
Balint's syndrome, spatial
disorders--
those don't clear up.
Anosagnosia patients
grow out of it.
Somehow, their brains
recover over time.
But again, it shows you
how much attention is
constructed, right?
Because they have the
stuff to represent
their arm, their disease.
That's all in their
mind and brain.
But the state they're in because
of the brain injury
lets them not construct
that reality.
So now, I'm going to show
you measures of neglect.
This is in your list just for
your notes, but sort of fun
just to look at the examples.
So here's a patient.
With these patients, they
typically have right sided
lesions, so the neglect is to
the left half of the world.
And here's a patient going to
the bathroom as if all you can
do is make right turns instead
of going this way, as if the
world weren't there, to
proceed on the left.
Here's another test
that happens
every day in a hospital.
The physician has drawn
these lines and says,
cross out the lines.
It's not perfect.
The patient does that one.
But look, they cross out
all these lines.
And the left half ones are
mostly left uncrossed.
It's as if they weren't there.
Here's what's called a
cancellation test.
There's lots of letters here.
And their job is to cross
out all the A's.
Now, let me start
with neglect.
You see over here,
this whole area?
Nothing is circled
or crossed out.
And you could say, well, what
would happen if instead of
neglect, you were like one of
those blindsight patients who
had a big lesion in the
cortex and you were
blind on one side?
What would you do there?
Well, it's easy for those
patients because what they do
is they don't see part
of the world.
But what do they do?
They turn their head, just
like you would do.
They turn their head.
They don't see it, but they
know they don't see it.
And they turn their head.
And a patient who's blind on one
side, loss in the visual
field, gets all the lines
because all you have to do if
you're blind on one side
is turn your head.
It's not that hard in
a practical sense.
But if you don't imagine the
left half of the world exists,
where would you turn
your head to?
And that's what these neglect
patients do, don't imagine the
left half of the world exists.
So here's an example of a
patient reading a text.
They're handed this text.
The slash lines here are where
this patient seems to think
the left side of
the page stops.
OK So they're overcoming
everything they know about how
a sentence should be and
reading this passage.
The patient says, "had to pass
the windows whom good morning
message for the ground his with
all his and he bottle."
Thank you very much.
It's right in front of them, but
the left half of the page
is just not present for
this person's mind.
Here is a person copying
a flower.
A psychologist or a neurologist
draws this flower
or has a flower ready to go,
a drawing, and says copy
everything you see.
And it's not always totally
perfect exactly how it works.
But you can see there's a lot
of the left side of this
flower missing--
right in front of them.
Here's a very simple one, too.
Copy everything you see here.
And what they see is these
three things up here.
Their job's to copy everything
down here.
They have all the
time they want.
Left side is neglected.
And all they copy
is the triangle.
That's all they draw.
And the tester will always
say, are you done?
Are you sure you're done?
The person says, I'm
sure I'm done.
Thank you very much.
Sometimes, they do something
remarkable.
They're shown a scene
like this.
Here's four trees with a
house in the middle.
And you can see this patient
starts over here.
They say, oh, there's a
tree over, draws this.
There's a house over here.
And they jump from location
to location.
Every time their attention
lands, they draw the right
half of it.
It's always as if the
left were missing.
And again, this idea of how
constructed this is.
Here's two more examples.
And the clock thing, we'll
talk a fair bit about.
Here's a patient writing
to dictation.
The first sentence, they
sort of stay--
but now, it's as if they
were running out
of room on the page.
It's like they're reading,
but it's writing.
The left half of the
page doesn't exist.
Clocks are used a lot in this
land, because it's kind of
impressive.
And we'll come back in a couple
different versions
about this.
But look at that.
They were asked to draw
the time on a clock.
And it's as if they could draw
the time on the right side,
their good side.
But it's as if the left half
of the clock didn't exist.
Here's another patient asked
to draw the time.
And you see almost what seems
like a struggle in the
patient, right?
They start on the right side.
And then here, they're
running out of space.
They've got to cram
in that 10.
Their mind knows it
goes to 12, right?
But there's no space
to put it in.
And so you put them, in a sense,
in a sense of conflict.
And that's the top version.
The bottom, they were given
numbers one at a time.
They were given, it tells
you here, 12 and 6.
So they put those in
the right spots.
Here comes 11.
Already, 11 is like,
uh-oh, right?
And then, they get 4, 9.
9 is not going to make it.
And 10, they know it has to come
after-- you can see that
they put them actually in a
struggle between what they
know, something about where the
numbers ought to go, but
the impossibility of the
left half existing.
Now, here's something-- and
we'll come back to this in a
few minutes--
what happens if you just give
them a piece of paper and say,
write down 1 o'clock.
And then, you take that
piece of paper away.
Write down 2 o'clock.
Take that piece of paper away.
Then look--
6, 7, 8, 9, 10, those
are not bad, right?
If they just do one of them, the
very same patient who had
to crowd everything on the right
is quite comfortable in
putting down a pretty good
9, 10, and 11 if
it's just one of them.
We'll come back in a little bit
to experiments that help
understand what's going on this
case because we don't
only want a scientist
to say, wow, this is
unbelievable and amazing.
We like to say something more
about how the mind is doing
this and what part of their
brain is important.
And kind of impressively, here's
a patient with eyes
open mostly crowding
on the right.
Got the 10 on the left, but
doing a better job when their
eyes are closed.
They missed the dial
altogether.
Their eyes are closed.
But they actually do it--
the same patient
does a better job.
OK, so how does that work?
And one more thing to mention is
that neglect occurs across
modalities.
That is, when these patients
have neglect, I
focused on the visual.
But these patients also don't do
very well if they're doing
things like reaching
for things.
It's not just vision.
It's pretty much everything in
the left half of the world.
And you can do these kinds of
things which, again, show not
only their neglect but the
constructed psychological
nature of the neglect.
It varies in ways that
are interesting.
So they're given a line
like this and say
mark the exact middle.
You would draw something here.
They draw here because they're
going to neglect
that part of the line.
Then, they say read the A.
So they draw the person's
attention to A. And now draw
it, and they get better.
Then, they're asked to
mark the middle.
Not too good.
Mark the middle-- but you
see the difference here.
The A is present or
the B is present.
And if the B is present, it
pulls them over here.
If the A is present, it pulls
their attention over here.
They put their hand at
the middle and say.
Now, please mark the middle.
Their hand goes over here
for the middle.
But if they start them all the
way over here, their hand will
only go this far.
So as you see, all these
different movements are
telling you that the mind
is interpreting what the
world is out there.
If you pull a little bit the
person to the left, they'll
notice a little bit
more of the left.
Where is the injury?
So almost everywhere you read
still in neurology books to
this day that it's in
the parietal cortex.
But in the last few years,
people have mostly come to
this idea that the damage
tends to be in
the temporal lobe.
And what happens when the
temporal lobe is injured, it
knocks of the balance of
attention in the left and
right parietal cortex.
And there's something about
the activity in the right
parietal cortex goes way down.
That's paying attention to the
left half of the world.
And as patients recover from
this, the balance comes back.
And that's actually been
measured now by brain imaging.
Their attention comes back
clinically, and it does in
most patients.
Then, the balance between the
two parietal cortices get
reestablished.
So even though people thought
the site of damage was here,
the interpretation's usually
here in the temporal lobe.
But the consequence of that is
reduced activity in this part
of the brain, even if it's
not physically injured.
The fantastic thing is--
think about this for a second--
in order to ignore
the left half of the flower, the
left half of a design, the
left half of a page, the left
half of a clock, what do you
have to know?
Where the left and right are.
It's not as if his
eyes were closed.
If your eyes were closed, you
wouldn't know where left and
right are on a page, right?
He has to represent in his mind
what is left and right
reasonably accurately.
And then, he extinguishes
awareness that anything in the
left could exist.
But part of his mind has to know
what is left for that to
work, right?
Otherwise, the digits would be
all over the piece of paper,
not even on the paper.
He centers on the paper.
He centers on the circle.
Centering means I know
what's left.
I know what's the center.
And then boom, the left
disappears as a place that
could exist.
So these are all tasks
in front of you.
There's been some incredibly
Sherlock Holmes like clever
experiments asking whether you
also neglect your imagination.
Not what's in front of you,
but your imagination.
So here's the way they did it.
Have any of you been in Milan?
There's a central cathedral
in part of town.
It's a big deal.
So they took Milanese patients,
people who lived in
Milan their whole lives who
had strokes in the right
hemisphere who had neglect, and
they asked them to imagine
the Piazza del Duomo, the major
church there, looking at
it from one side of the square
or from entering from the
opposite side of the square.
And I'll show you the
other experiment.
Here's the idea.
They said imagine that you're
entering the square this
direction so that the church
is behind you, or this
direction so that the church
is in front of you.
So you're entering the square
from one side or from the
other side.
Now, the square that you've been
too many times, that you
know very well, tell me
everything that's in the
square as you imagine entering
from one side.
And here's what the
patient reports.
They're imagining coming
out facing the church.
And they report these kinds
of things from this side.
If that's only on the
right side, they're
ignoring the thing.
So they say there's a cafe.
There's a bookstore or whatever
else there is here.
That's everything that's
in the square.
Everything that's in the
square is shown in red?
Everything that's
in the square.
They wait just moments.
And they say, now imagine
instead you were coming out
from the church, opposite
view of the square.
Tell me everything that's
in the square.
And here's what they tell you.
The items that are in blue--
and they don't tell you the
items they just told you, the
locations they've just told
you circled in red.
So they're sitting their
imagining their square.
And then, they will ignore
everything on the left,
whatever's their subject
of left.
And you know they know it
because all they have to do is
imagine they're on the opposite
side of the square,
and then they report.
Does that make sense?
They're ignoring the left half
of what they imagine the
square looks like when they've
been to it many times.
And here's another patient doing
exactly the same thing.
Imagine you're coming
out of the church.
What's in the square?
Well, here's some specific
places I know.
That's it?
That's it.
Wait a minute.
Imagine you come this way into
the square facing the church.
What's everything
in the square?
And they only report the
things on this side.
So they're ignoring-- yeah?
AUDIENCE: Does the patient
realize after a few seconds?
PROFESSOR: No, they never do.
It's an excellent question.
They just answered a moment
ago one side, right?
Why don't they tell you, I just
told you the stuff on the
other side?
Because it's as if it
couldn't exist.
It's a little bit analogous
to the patient
whose arm isn't moving.
And you go, do you
have any problem?
And they go, no, I don't
have any problem.
It's as if there couldn't
be a problem.
What are you talking
about, right?
So it overcomes all their
knowledge and all their
intelligence.
It's as if I forced you to guess
in detail what's in the
back of the room if something
new was there.
And you go, there's no way.
I can't see.
I have no eyes in the
back of my head.
It's sort of like that.
It's as if the left half
couldn't exist.
The contradiction they
could note--
just a moment ago I told you
the other one-- they don't
notice it because something
about this neglect swallows up
all of your judgment.
It's beautifully phrased by some
neurologist as, it's as
if the left half could
not exist.
Whenever you're thinking
left, it doesn't exist.
And ironically, you have to
think left for that to work.
That's the amazing thing.
You have to go, I'm
in the middle.
There's a left.
There's a right.
Now, the left doesn't exist.
And it couldn't exist.
And every hint I get that it
does exist, like there's food
on that side or the pages
usually go all the way here
and makes the sentences make
sense, it all disappears on
you because it couldn't
possibly exist.
And the neat thing about
that is it's striking
neurologically.
But that means in our own heads
as we go around, we're
constructing the world this way,
building up two separate
sides of our brain that are
gluing together a picture of
the world around us.
And these patients lose
that glue on one
side of their brain.
Is that OK?
Here's another version.
It's less flashy, but
it's the same idea.
Now, neglect can't
get small enough.
If you make something
very tiny, then you
don't ignore the left.
Once it gets tiny enough,
you can't do it.
So they took advantage
of that.
And they show cloud like
stimulus of these.
But they didn't show
them like this.
They only had a slit.
So you only saw the cloud
a bit at a time.
And you see one cloud, and then
you see another cloud.
Perhaps you'd see this cloud
go by, and you see
this cloud go by.
And your job was to say were
they identical clouds or not?
And if they were not identical,
on which side do
they differ?
So because of all your visual
experiences through the slit--
which is too small for
neglect to happen--
what you do is you create in
your mind's eye what does that
whole cloud look like as it
passed through the slit in
your mind's eye?
And then, you see another one.
And you put that up in
your mind's eye.
And you compare these two
things that are in your
imagination in your
mind's eyes.
And what happens is if these two
things differ on the left
side, the patients rarely can
make that distinction.
It's not because they
can't see it.
It's always in that
narrow slit.
But once they put the pieces
together, they put it up in
their mind, the left half
disappears on them in their
mind's eyes.
So here's an experimental
approach to think about what
might be going wrong
in these patients.
So they used a very simple task,
which is when a light
comes on, you push a button.
That's all the task is.
Any light comes on,
you push a button.
And sometimes, they'll
put an arrow.
And sometimes, you have
no information.
The light comes on on the
left or the right.
And sometimes, they'll put on
an arrow in the middle that
will warn you whether the light
is likely to come on in
the left or the right.
So sometimes, you have
neutral things.
You get a cross in the middle.
Then, a light comes on.
You don't have to say
left and right.
You just push a button when
one of those goes on.
Sometimes, he gets an error
that's called valid that, 80%
of the time if it's pointing
this way, it will turn out on
that side, 80% it will
turn on this side.
So 80% of the time,
it's honest.
And 20% of the time,
it's dishonest.
So here's what it looks like.
You're looking here at
a computer display.
That thing disappears.
And then, either an
x is here or here.
And you push a button.
That's all.
Or a light comes on, and
you just push a button.
That's all.
If it came on on the left or
the right, I push button.
When an arrow appears, 80% of
the time it's warning you
where that light will appear.
20%, it's dishonest and it
appears on the opposite side.
So you will know, how good an
experimental psychologist you
are right now, if I ask you
which condition do you think
you're the fastest to push the
button, when you have an arrow
that's truly telling you where
the light will come on, an
arrow that's misleading
you, or an x
that tells you nothing?
Which do you think you'll
be fastest?
PROFESSOR: Where the arrow's
pointing, right?
Like, here's the answer,
over here!
OK, thank you very much.
Which do you think you'll
be slowest on?
The dishonest arrow, right?
The arrow says, look over
here, look over here!
And you're looking over there.
And you go, oh no!
It came on the other side.
You lied to me!
And the x is the middle.
And here's the data.
And it's a very simple
experiment, right?
How fast are you?
This is reaction time just
to push a button
when it comes on.
Here's the neutral condition
in the middle.
You're a little bit faster
if it's an honest arrow.
You're a little bit
slower if it's a
dishonest, misleading arrow.
So now, you do this
exact experiment.
And I'll show you the data.
And then, I'll simplify it for
you with patients who have
right sided damage, left
sided neglect.
And you can see as you look at
these lines that the arrow can
be honest or dishonest,
and it can be on the
left or right side.
Now, if you were always bad on
the neglected side, you go,
well, that's not
a big surprise.
But here's a surprise.
Patients were only bad--
the times were way up here only
when they had a dishonest
arrow that sent them into
their good side.
That's when they were
really bad.
So let's take a look
at this again.
So here's the bad side.
Here's the good side.
When that arrow comes on
that's honest, good.
When an arrow comes on that's
honest this way, they do fine.
That's their bad field,
but they do fine.
Tiny bit slower, but
just a tiny bit.
Arrow comes on that moves them
into their bad field but
really the light is on
here, they do fine.
But if an arrow sends them into
their good field, then
they're really, really slow
to get back here.
So Posner argued that when you
move your attention in the
world, you have three steps
you have to do.
You have to disengage your
attention from where you're
paying attention,
just logically.
I'm paying attention
here right now.
I'm going to pay attention
over here.
I have to pull myself up from
here, move my attention over
here, and then focus here.
So you disengage, get out from
where you are, move to where
you need to go, and land
and then focus
what you want to do.
And the only condition where
they're bad is where they have
to get their attention out of
the good field as if once
they're in that good field, once
their mind is landed in
that good field, they're
in quicksand.
And it's going to be really hard
to get their attention to
move into the bad field.
So think about this.
The clocks are perfect for this
because when you draw a
clock mostly--
think about that as
intuitively--
if I was to ask you to draw the
numbers on a clock, you
start with a 12 typically.
Then, what's the next
one you would draw?
One, because that's how we're
taught to do clocks.
Disaster if you have neglect.
You're in the good field.
Now, the left half of the clock
has disappeared on you
because the clock has made you
land your attention on the
good field.
And now, you can't
pull out of it.
But what happens if you only
have to draw 8 o'clock?
Your attention never got moved
into the good field.
It's just starting from
middle, so to speak.
And this very same patient can
draw the 8 o'clock or 10
o'clock pretty well.
Does that makes sense?
Because they never got stuck
in the good field.
They only moved into
the bad field.
They can move into
the bad field.
And so if their eyes are
closed, that's better.
They get less stuck.
And now, we understand
this thing.
Why is it these patients, if
both fingers are moving--
because once their attention is
drawn into the good field,
it's as if the bad field
disappeared on them.
But if they only get stimulated
in the bad field,
so right side here, then they're
OK because they never
paid that much attention
to the good field.
So this is a nice experiment.
It shows you what
is the problem.
The problem is once you're
paying attention to the good
field, the normal, healthy
field, it's so powerful
compared to the weakened
representation here, that you
never leave it because it just
seems like everything.
Now, here's a clever one.
Again, this shows you how much
of attention is created by our
minds as opposed to just
simply defined by the
environment.
So what if you show a display
to somebody with neglect and
then rotate the display right
in front of them?
So initially, the neglect is
going to be on the left side.
But imagine the thing is turning
over like this, right
in front of them.
Will the neglect travel with
the initial assignment?
So this is from Marlene
Behrmann, a very clever
experiment.
They have to pay attention
if the light
comes on here or here.
But what they do is while the
experiment's going on, right
in front of you, it slowly
rotates over to here.
And sure enough, then
the light comes on.
Sure enough, the neglect now
moves into the good field
because once you've assigned
left and right, you
know this is left.
So OK, you turn it over.
That's still really left.
But think how weird that is.
The mind is deciding that.
In an absolute sense, this
thing is on the right.
But the mind said, this
is the leftward one.
And you can flip it over, but
you're not tricking me.
I know it's on the left, and
I'm considering it the
leftward one.
The mind is deciding what
counts as left and
right, not the world.
And what other kinds of
information is being processed
that's not reaching
attention levels?
So here's a cute experiment.
They would say to these
patients, any difference
between these two things?
No.
But if you had to live in one of
these houses, which one do
you think you'd live?
Well, I don't know.
They're pretty much the same.
Why would I pick one?
Well, pick one!
They go, ah, this looks like a
little better place to live if
I have to pick one.
Which vase do you want?
I don't know.
They look the same.
You have to pick.
I pick this one.
Which glass to drink from?
You have to pick.
Pick this one.
So they consciously are not
aware of what's going on here
when there's information to
the opposite side to draw
their attention.
But something in their mind
somewhere is picking up
information.
So the last question-- and I'll
show you a final video--
is this.
What kind of information is
picked up in the neglected
field as you decide, some part
of your mind, to neglect it?
So imagine if I showed
you two forks versus
a fork and a spoon.
In order for that to make a
difference whether you report
both are present-- so again,
if you have a right sided
lesion, you might tend not to
report this fork or not to
report this key.
If you just don't report either
one, OK, left is left
and you're bad at reporting
that one.
There's something competing
in the good field.
Your attention gets drawn
here, hard to disengage.
But if it makes a difference
what this thing is, that means
that your mind kind of
knows what it is.
And your mind is saying, well,
if it's a key, that's
different enough that I can
still pay attention to it.
But if it's another fork, those
are really similar.
And now, my mind is really
sucked into this fork.
But in order for that to make a
difference, do you see that
you have to know somewhere in
your mind what's different on
the left for that to affect
your performance?
So now, we'll see a video of
a patient, the last one.
This is a neurologist, Bob
Rafal, and a patient.
It's a hugely nice thing of the
patients, most of all, but
also the physicians to make
these tapes available for
teaching purposes.
So you understand--
just review for one month
and we're done--
that when the same object came
up, did he pretty much notice
the one on the bad side and
the right side for him?
No.
Same object, he almost
always said it's one.
If they're different objects, he
typically reported slightly
sluggishly the one
on his bad side.
That means part of his mind has
to know what the object is
so that he ignores it if it's
identical and he reports it if
it's different.
Well, you have to know
what it is to base
your answer on that.
Yet, the logic of neglect is
that if they're identical,
then he's going to ignore the
one that he spotted on the
left in part of his mind but
squashed from his awareness on
the other side.
OK, thanks very much.
