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ELIZABETH SPELKE: I want to start with an observation
about this summer school.
There's a lot of development in this summer school.
You've got two full mornings devoted to it-- today
and on Thursday.
It also came up pretty majorly in Josh Tenenbaum's class
last Friday and I learned early this morning
also in Shimon Ullman's class that I couldn't be here
for yesterday afternoon.
And the issues have come up in many other classes as well,
including Nancy's, Winrich Freiwald's, and so forth.
Now, what's come up is not only the general questions
about development, but specific questions about human cognitive
development.
Questions that have been addressed primarily
through behavioral experiments, not
experiments using neural methods or computational models.
And the topic that I'm going to be trying to--
that Allie and I will try to get you to think about
for this morning is even narrower than that.
It's about the cognitive capacities of human infants.
And I think a fair initial question would be,
why so much focus on early human development?
And that question will get sharper
if you look at where major organizations are
putting their research money.
They are not putting it into the kind of work
that I'm going to be talking about today.
There is no-- in the Obama BRAIN Initiative,
where they're looking for new technologies,
there's no call for new technologies
to figure out what human knowledge is
like at or near the initial state
and how it grows over the course of infancy.
And the European Human Brain Project
doesn't have development as a major area in it, either.
So I think it's fair to ask, why is CBMM
taking such a different approach and putting so much emphasis
on trying to get you guys to think about and learn
about human development?
And two general reasons, I think.
One is, it's intrinsically fascinating.
Come on.
We are the most cognitively interesting creatures
on the planet.
And we're extremely flexible.
At the very least, we know that a human infant can grow up
to be a competent adult in any human culture of the world
today and any human culture that existed in prehistory.
And that means extremely varied--
they've had to learn extremely different things
under different circumstances and have
succeeded at doing that.
We also know that by the time they start school,
if they go to school at all, the really hard work
of developing a common-sense understanding of the world
is done.
That is, it's not explicitly taught to children.
Most of it isn't even very strongly
implicitly taught to them in the form of other people trying
to get them to learn things.
What you're trying to do when you have a young kid,
as those of you who have them know, or have had them know,
is you're trying to get them not to climb off cliffs or explore
the hot pots on the stove and so forth.
You're really not spending very much of your time trying
to get them to learn new stuff.
They're doing that on their own.
So it's I think a really interesting question,
how do we do that?
Intrinsically interesting in its own right,
even if it were of no other use to us.
But historically it's also been recognized
as being really important for efforts
to understand the human mind, understand the human brain,
and build intelligent machines.
So Helmholtz, who came up in Eero's talk last night,
was not only a brilliant neurophysiologist
and a physicist, he was extremely interested
in perception and cognition.
And he wrote about fundamental questions
about human perceptual knowledge and experience.
How is it that we experience the world as three-dimensional?
He concluded that we didn't know the answer
and never could know the answer, unless we
could find ways to do systematic experiments on infants
of the sort that could already be done to reveal mechanisms
of color vision, for example, as were described
last night on adults--
systematic psychophysical experiments on infants.
But he looked at infants and said,
I don't see any way to do that.
We can't train them to make psychophysical judgments and so
forth.
But he was aware of their centrality.
So was Turing, who in thinking ahead
to how one might build intelligent machines,
suggested that one aim to build a machine that
could learn about the world the way children do.
And a side of the work that's come up
so many times in the whole Hubel-Wiesel tradition that
started in the late '50s, I think
one of the most exciting and important developments
within that field, we're not just
focusing on the response properties of neurons
in mature visual systems, but rather
on the development of those neurons
and the effects of experience on them.
When you discover that you get these gorgeous stripes
of monocularly-driven cells in V1,
it then immediately became really interesting to ask,
suppose an animal were only looking at the world
through one eye?
Or suppose they could look at the world through the two eyes,
but not at the same time, or not at the same things
at the same time?
What would happen to those cells?
And there was gorgeous work addressing those questions
from the beginning.
Now, that work has somewhat receded from attention.
I think that's a mistake.
I think that there's a great deal
to be learned from those kinds of studies now.
And if I get nothing else across over this time,
I hope you'll at least get the idea
that this is a field worth following, looking
at development in humans, looking at development
of perceptual and cognitive capacities
in animal models of human intelligence as well.
So more specifically, I think there
are three questions about human cognition
for which studies of early development
in general and in human infants in particular
can shed light on.
Two of them I'm not going to really be talking about today,
except indirectly.
One is the question, what distinguishes us
from other animals?
We come into the world with very similar equipment.
But look what we do with it.
We create these utterly different systems of knowledge
that no other animal seems to share.
What is it about us that sets us on a different path
from other animals?
That's question one.
And the other question I won't talk about is--
well, I'll talk about it a tiny bit, but not
directly-- is, where do abstract ideas come from?
It seems like we not only develop systems of knowledge,
but those systems center on concepts
that refer to things that could never in principle
be seen or acted on.
Like the concept "seven," or the concept "triangle,"
or the concept "belief," or ethical concepts and so forth.
Abstract concepts organize our knowledge.
But since they can't be seen or touched or produced
through our actions, how do we come to know them?
I think studies of early development
can shed light on that as well.
But the question I want to focus on today is the third question,
and it's the one that Josh raised on Friday.
How do we get so much from so little as adults?
As adults, you look at one of the photographs
he showed of just an ordinary scene
and you can immediately make predictions about,
if you were to bang it, what would happen?
What would fall?
What would roll?
We seem to get this very, very rich knowledge
from this very, very limited body of information
at any given time.
And what that suggests is that we
are able to bring to bear in interpreting
that scene a whole body of knowledge
that we already have about the world and how it behaves.
But that raises the question, what is it that we know
and how is our knowledge organized?
What aspects of the world do we represent most fundamentally?
Which of our concepts are most important to us
and generate the other concepts and so forth?
How can we carve human knowledge at its joints?
And now this can be studied in adults
and you've seen a number of examples of this.
You saw it in Nancy's talk last Tuesday, right?
Anyway, last week sometime.
Studies using functional brain imaging
to get at our representations of human faces.
You saw it in Josh's talk.
He was mostly using data from adults
to be probing the knowledge of intuitive physics
that he was focused on and that his computational models are
trying to capture.
You're going to see it on Thursday in--
no, tomorrow in Rebecca Saxe's talk,
where she'll talk about human adults' attributions of beliefs
and desires and other mental states to people.
It's certainly studyable in adults,
but it's difficult to answer these questions.
It's difficult to answer these questions in any creature,
but I think it's especially difficult
to answer these questions in adults for a couple of reasons.
One is that our knowledge is simply too rich.
By the time we get to be adults, we know so much
and we have so many alternative ways
of solving any particular problem,
that it's a real challenge to try
to sift through all our abilities
and figure out what the really fundamental, most fundamental
concepts that we have are.
And the second problem with adults
is we not only know too much, we're too flexible.
We can essentially relate anything to anything.
We can use information from the face
to answer all sorts of questions about the world.
And here, I think, infants are useful for a maybe seemingly
paradoxical reason.
They're much less cognitively capable.
They know much less about the world and they're
far less flexible--
I'll show you examples of this--
far less flexible in the kinds of things
that they can do with the knowledge that they do have.
Nevertheless, they seem to come into the world equipped
with knowledge that supports later learning.
And because it's supporting later learning,
it's being preserved over that learning.
It's being incorporated in all of the later things
that we learn.
So it remains fundamental to us as adults.
And I think this can help us, to think
about how our own knowledge of the world is organized.
OK.
So that's a general overview.
How do we study infants?
Now here's where the tables turn radically.
We have way better methods for studying cognition in adults
than we do in infants, just as Helmholtz thought.
They can't talk to us.
They don't understand us when we talk to them,
so we can't give them structure.
Oh, and unlike willing trained animals,
you can't train them to do things,
at least not in any extended sense.
They can't do much.
I'm most interested in infants in the first four
months of life before they even start reaching for things,
much less sitting up by themselves or moving around.
The interesting thing is, from day one, from the moment
that they're born, they're observing the world.
They're looking at things and they're getting information
from what they see.
Now, their observations-- we've learned over the last half
century or so that their observations are systematic
and they're reflected in very simple exploratory behaviors,
like when a sound happens somewhere in the visual field,
turning the head and orienting it toward the sound.
Even newborn infants will do that.
Or if something new or interesting is presented,
infants will tend to look at it.
And these behaviors I think can tell us
something about what infants perceive and know.
And before getting to the real substance of what
I want to focus on today, let me give you
a few examples of this.
What kinds of things do infants look at?
Well, if you present even a newborn infant--
infants at any age, really--
with two displays side by side, and vary
properties of those displays and the relation between them,
you'll see that they look at some things more than others.
So they'll look at black-and-white stripes
more than they'll look at a homogeneous gray field.
That's useful.
It allowed people to get initial measures
of the development of visual acuity which infants--
it actually overturned a somewhat popular view
that at birth, infants couldn't see at all.
We know from these simple studies that they can.
And we also know that their acuity starts out very low
but gets pretty good by the time they're
four to six months of age.
It doesn't reach full adult levels until about two years.
We also know that they look at moving arrays
more than stationary arrays, and they
look at three-dimensional objects
more than two-dimensional objects.
In addition to having intrinsic preferences
between different things, they also
have a preference for looking at displays that change
or displays that present something new.
So jumping from the '50s when those first studies were
done up to the '80s, there was a whole flurry
of studies showing babies pairs of cats on a series of trials
and then switching to a cat and a dog.
And the babies would look longer--
these are three-month-olds-- would
look longer at the dog than at a new example of a cat.
So they're able to orient to novelty.
And they also look longer at a visual array
that connects in some way to something they can hear.
Now, one of the things I spend a lot of my time studying
is foundations of mathematics-- numerical and spatial cognition
in infants.
I'm not going to talk about it at all today.
But I kind of couldn't resist giving just one example
of looking at what you hear that connects to infant sensitivity
to a number.
This is a study that was conducted in France
by Veronique Izard and her colleagues
with newborn infants in a maternity hospital.
She played infants sequences of sounds,
and each sequence involved repetitions of a syllable.
For half the infants, each syllable appeared four times.
For the others, it appeared 12 times.
And for the ones for which it appeared four times,
each syllable was three times as long.
So the total duration of a sequence
was the same for the two groups, but one
involved four syllables and one involved 12.
And after they heard that for a minute,
the sound continued to play and now she showed,
side by side, an array of four objects
versus an array of 12 objects.
And the babies tended to look at the array that
corresponded in number to what they were hearing.
Now, all of this gives us something to work with,
but it raises a nasty problem.
And the problem is, what are babies
perceiving or understanding?
Today we're not going to be asking,
how can babies classify things?
What do they respond to similarly?
What do they respond to differently?
We're going to be asking, what sense do they make of them?
What are they representing?
What the content of the representations
that they're forming in each of these cases?
And these studies as I've just described them don't tell us.
Let's take the case of the sphere versus the disk.
When this study was first conducted,
the author concluded that babies have depth perception,
that they perceive three-dimensional solid
objects.
Is that a justifiable conclusion?
AUDIENCE: Not necessarily.
ELIZABETH SPELKE: Why not?
AUDIENCE: Because they are not [INAUDIBLE]..
ELIZABETH SPELKE: Yeah.
OK.
So when you present things that differ in depth,
you're presenting a host of different visual features
that for us as adults are cues to depth.
The question is, are they cues to depth for the infant?
And the fact that the infant is looking longer
at something we would call a sphere than at something we
would call a disk, doesn't tell us whether they're looking
longer because they're thinking, "sphere,"
or "3D," or "solid," or something like that,
or whether they're looking longer because they're seeing
a more interesting pattern of motion
as they move their head around, or because as they converge
on one part of the array they're getting interesting differences
in how in-focus different parts of it are, and so forth.
All of the different cues to depth
could-- what we want to know is, what's
the basis of this preference?
And the existence of the preference
doesn't tell us that.
Similarly for the cats, and similarly
for this single isolated experiment
that I gave you on number, right?
Does this say anything whatsoever about number,
or could there be some sensory variable
where there's just more going on in a stream of 12 sounds
and there's more going on in an array of 12 objects,
and babies are matching more with more, independently
of number?
These studies in themselves don't tell us.
In order to find out, what we need to do
is take these methods and do systematic experiments.
And these experiments work best under the following conditions.
When you're studying a function that exists in adults
and whose properties have been explored in adults in detail
systematically, when you have a body of psychophysical data
that you can rest on in your understanding of what's
happening in adults, and you can then apply that to infants.
So one example of that took as its point of-- this
is work by Richard Held, a wonderful perception
psychologist who worked at MIT.
Still is active, actually.
He's retired but still active.
And he did these beautiful experiments
that started with the sphere-versus-disk phenomenon.
And first of all, he tried to take it apart
and say, let's just focus on one cue today, OK?
Binocular disparity at the basis of stereo vision.
So he put stereo goggles on babies.
These were babies ranging in age up to about from birth
to about four months, I think.
He put stereo goggles on them and showed them, side
by side, two arrays of stripes.
In one of the arrays, the same image went to both eyes.
In the other arrays, the edges of the stripes
were offset in a way that leads an adult
to see them as organized in depth-- some stripes in front
of others.
And he showed that infants looked longer at the array with
the disparity-specified differences in depth than
the array where it didn't.
He did not conclude from that that they
have depth perception, but it gave him
a basis for doing a whole series of experiments that asked,
in effect, do you see this effect
under all and only the conditions in which adults
have functional stereopsis?
So he showed, for example, that if you rotate the array
sideways 45 degrees so that you still
have double images on the stereo side,
but we wouldn't see depth because our eyes are
side by side, not one above the other, the effect goes away.
He varied the degree of disparity
and showed that you only get this preference
within this narrow range where we have functional stereopsis.
And he was able to show the striking continuity between all
of the properties of stereo vision
in adults and in these infants.
So that study and a bunch of others using other methods,
I think have resolved this question of whether depth--
when depth perception begins.
Its beginning very early.
Stereopsis comes in around two to three months of age.
Other depth cues come in at birth.
It's beginning very, very early.
But it didn't come from single experiments.
It came from systematic patterns of experiments.
In the case of cats versus dogs, we don't really
have a psychophysics of cat perception,
but steps have been taken to try to get to what the basis is
of infants' distinction between dogs
and cats in those experiments.
And interestingly, what's popped out are faces.
Turns out, you can occlude the cat and the dog's whole bodies,
and if you leave their faces, you get these effects.
If you occlude their faces and leave their bodies,
you mostly do not, unless you cheat and give
other obvious features, like all the dogs are standing
and all the cats are sitting, or something like that.
But in the normal case, faces are coming out
as an important ingredient of that distinction.
In the case of abstract number, there's
also a lot of work in adults on our ability
to apprehend at a glance approximate numerical value
of sounds in a sequence or visual arrays.
We've learned a lot about the conditions under which we can
do that and the conditions under which we can't.
That's not my topic for today, but Izard and her collaborators
have been testing for all of those conditions
in newborn infants.
And so far, so good.
It looks like there is a similar alignment
between the patterns of--
the factors that influence infants' responses
in those studies where they hear sounds
and see arrays of objects and the factors
that influence our abilities to apprehend approximate number.
OK.
So this gives us some good news and some bad news.
The good news is that I think questions
about the content of infants' perception and understanding
of the world can be addressed.
The bad news is that we can't do it very fast.
You can't do it with a single silver-bullet experiment.
You have to do it with a long and extensive pattern
of research.
In the past, research on infants has gone extremely slowly.
Basically, the methods that we have
allow you to ask each baby who comes into the lab maybe one,
or if you're lucky, a couple of questions,
but not more than that.
So it takes a long time to do a single experiment.
I do think, though, that this work is
poised to accelerate dramatically
and that we're poised to--
this is a good time to be thinking about infant cognition
because I think we're soon going to be in a different world,
where we can start asking these questions at a much more
rapid pace.
That's for at least two reasons, both of which, by the way,
are being fostered by the Center for Brains, Minds and Machines
and undertaken by people who are part of that center.
One is, there are now efforts underway to be able to test
infants on the web.
These basic simple behavioral studies, you
can assess looking time using the webcam
in an iPad or a laptop, and you can test babies that way.
And there's attempts to do that, which
would make it possible to collect data doing
the same kinds of experiments that
have been done in the past, but much more quickly.
Two, as Nancy already mentioned and Rebecca
may talk about tomorrow, there are
efforts underway to use functional brain imaging
to get at not only what infants look at,
but what regions of the brain are activated when they look
at those things, which will give us
a more specific signal of what infants are attending
to and processing, someday, hopefully, in the near future.
And we just had a retreat of CBMM,
where there was a lot of brainstorming
about new technologies to try to get
more than just simple looking time out of young babies.
So maybe some of that will work as well.
But what I want to focus on today
is that even this slow, plodding research
has gone on for long enough at this point
that I think we've learned something about what infants
perceive and what they know.
And I tried to put what I think we learned into two slides.
Here's the first one.
I think that very early in development,
baby in the newborn period, but anyway,
before babies are starting to reach for things
and move around on their own, they already
have a set of functioning cognitive systems,
each specific to a different domain.
One is a system for representing objects and their motions,
collisions, and other interactions.
Another is a system for representing people
as agents who act on objects, and in doing so,
pursue goals and cause changes in the world.
A third is a system for perceiving people
as social beings who can communicate with, engage
with other social beings and share mental states.
And then three other systems that I won't talk about today.
One system of number, which I think
is being tapped in that first Izard experiment.
And two systems capturing aspects of geometry,
one supporting navigation of the sort that Matt Wilson studies,
the other supporting visual form perception of the sort that IT
and occipital cortex represent.
I think each of these systems operates as a whole.
In Josh's terms from last Friday,
it's internally compositional.
Infants don't just come equipped with a set
of local facts about how objects behave, they come equipped
with a set of more general rules or principles that allow them
to deal with objects in novel situations
and make productive inferences about their interactions
and behavior.
Each of these systems is partially
distinct from the other systems.
It's distinct in three ways.
First, each of them operates on different information.
It's elicited under different conditions.
Second, it gives rise to different representations
with different content.
And third, most deeply, it answers different questions.
So for example, we have two-- infants
have two systems for reasoning about people,
but each system is answering a different question.
The agent system is answering the question,
what is this guy's goal?
What is he trying to accomplish?
What changes is he affecting in the world?
The social system is asking, who is this guy related to?
Who is he connected to?
Who is he communicating with?
Each of the systems are limited, extremely limited relative
to what we find in adults.
Each captures only a tiny part of what
we as adults know about objects or agents
or social interactions.
Each of them, I think, interestingly,
is shared by other animals.
I didn't expect that to be true when
we started doing this research.
But as far as we can see so far, it's hard to find anything that
a young human infant can do that a non-human animal can't.
And I'll give you examples of that, too.
And finally-- and I won't talk about this much, unfortunately.
I think each of these systems continues
to function throughout life and supports the development
of new systems of knowledge.
So when we think thoughts that only humans think,
we engage these fundamental systems
that we've had since infancy and other animals share.
I also think this research tells us
something about how we do that.
I think that in addition to having
these basic early developing systems,
we have a uniquely human capacity
to productively combine information
across these systems, and through those combinations,
to construct new concepts.
I think these new concepts underlie,
or they tend to be abstract, and they
underlie a set of very important later-developing systems
of knowledge, including knowledge
that allow us to form taxonomies of objects, of tools,
of natural kinds like animals and plants,
and to reason about their behavior,
such that when we encounter some new thing,
we already know a lot about the kind of thing
that it is and can use that to infer many
of its specific properties, and also
to direct our learning very explicitly to fill
in the gaps in our knowledge.
Another is the systems of natural number
in Euclidean geometry.
Natural number, children seem to construct over the first three
to five years of life.
Euclidean geometry seems to take much longer, much, much later.
Molly Dillon, who's also here, has been trying to work
on understanding-- and so has Veronique Izard--
how children go from six years of age,
where they seem absolutely clueless about the simplest
properties of Euclidean geometry, to 12-year-olds who,
whether they're in the Amazon and have never been to school,
or studying geometry in school, seem
to have a basic rudimentary understanding of points
and lines and figures on the Euclidean plane.
A third is a system of persons and mental states.
And I won't talk about it, but I'm only
talking for the first half or so of this time,
then Alia Martin's going to take over.
And you'll touch on--
you'll get to some of those issues.
Now, as Nancy said last week, I have this out-there hypothesis
that I don't think anybody else in the world believes,
but I still believe it.
That this productive combinatorial capacity
either is or is intimately tied to what's
the most obvious cognitive difference between us
and other animals, namely our faculty of natural language.
In particular, I think that there
are two general properties of natural language
that make it an ideal medium for forming combinations
of new concepts.
One is that the words and the rules of--
well, three properties, actually.
One is that the syntactic and semantic rules
of natural languages are combinatorial and
compositional.
That is, if you learn the meanings of words
and you learn how to combine them,
you get the meanings of the expressions for free.
You don't need to go out and learn
what a brown cow is if you know what brown is
and you know what a cow is.
Second, the words and the rules of natural language
apply across all domains.
They're not restricted to one domain or another the way
infants' other cognitive capacities seem to be.
So if you learn how "cow" behaves
in the expression "brown cow," and then you hear "brown ball,"
or something that a different domain of core knowledge
would be capturing, you can immediately
interpret that combination as well.
And then the last thing about natural language that I think
makes it so useful for cognitive development is that it's
learned from other people.
And other people talk about the things
that they find useful to think about, right?
Word frequency is a really good proxy
for what the useful concepts out there are.
So a child who has a very powerful combinatorial system
that can create a huge set of concepts
is going to have a search problem when they try to apply
those concepts to the world.
Something will happen in the world.
And if they now have a million concepts
that they could bring to bear, which one are they
going to use?
Are they to test them all out?
Having too many concepts, too many innate concepts,
would not necessarily be a blessing.
But if you use language to guide you to the useful concepts,
I think you'll do better.
The ones people are going to talk about around
you most frequently are going to be the ones that it's
going to be most useful for you to be learning at that point.
So let's go back to that first set of questions, which is what
I want to be focusing on today.
And as I said, I'll talk particularly
about three domains where infants
seem to develop knowledge quite rapidly
over the course of infancy.
And I'll spend most of my time on the first one, objects.
So object cognition is really interesting
and it seems to span this really big range.
It seems to involve many different kinds of processes.
If you're going to figure out what the objects are,
what the bodies are in a scene, then you
need segmentation abilities.
You need to be able to take an array like this
and break it down into units, figuring out
what different parts of that array lie on the same object
and what parts lie on different ones.
So early mechanisms for doing that
can participate in object representation.
But also to perceive objects, arrays are cluttered
and objects tend to be opaque.
And when they are, it's never the case
that all of the surfaces of one object
are in view at the same time.
And it's often the case that you're only
seeing a little bit of any given object at a time.
Yet somehow we're able to see this
as a continuous table that's extending behind everything
that's sitting on it, and even sort of as a continuous plate,
a single plate that's partly--
that's on the table behind the vase, and so forth.
So to represent objects, we've got
to be able to take these visual fragments
and put them together in the right sorts of ways.
Something that's harder to show in a static image,
but that of course is radically true about the world
is that our perceptual encounters with objects
are intermittent.
We can look away and then look back,
or an object can move out of view
and then come back into view, yet
what we experience is a world of persisting objects that
are existing and moving on connected paths,
whether we're looking at them or not.
And finally, objects interact with other objects
and we need to work out those interactions.
And the working out that I'm interested in
is not what this little boy is doing,
but what his younger sister is doing
as she's sitting in her infant seat
and observing him acting on these towers
and wondering what's going to happen next.
OK?
At least that's the problem on the table for today.
OK, so a standard view for a very long time
has been that different mechanisms solve
these different aspects of the problem of representing
objects.
That segmentation depends on relatively
low-level mechanisms.
Completion and identity through time,
it's going to depend on how much time we're talking about
and how complicated the transformations are.
They're sort of in the middle.
And this is all about reasoning, about concepts
that go beyond perception altogether,
like the mass of an object, which we can't
see directly, and so forth.
And I kind of believed that that was true when
we started doing this work.
And because I did and wanted to know where the boundaries were
of what infants could do, I started
by working on these problems here.
And that's what I'm going to talk about today.
But let me flag at the outset that I no longer
believe that the real representations of objects that
organize infants' learning about the physical world, I
no longer believe that they're embodied
in a set of diverse systems.
I think there's a single system that's ultimately at work here.
Of course it has multiple levels to it,
including low-level of edge detection, and so forth.
But that there's a single system at work that both--
that tells us what's connected to what
and where the boundaries of things
are in arrays like this, how things continue
where and when they're hidden, and how they interact
with other things.
That's one unitary system, and I'll
try to show you what evidence supports
that view, though, of course, jump
in with questions or criticisms or alternative accounts.
OK, so here's an intermediate case to start with.
You present a-- it was studied a lot by Belgian psychologist
Elvin Meshot back in the 1950s, I think-- '50s or early '60s.
Take a triangle, present it behind an occluder,
and ask babies, in effect, what do you see in that triangle?
Do you see a connected object or do you see
two separate visible fragments?
We did these studies with four-month-olds
because they're not yet reaching for things
and manipulating objects.
We used the fact that they tend to like
to look at things that are new.
So we presented this display repeatedly-- we, by the way,
is Phil Kellman, now at UCLA and studying
all this stuff in adults primarily, also
studying mathematics now.
Anyhow, so we presented displays like this repeatedly
to babies until they got bored with them.
And then we took the occluder away and in alternation,
presented them with a complete triangle
and with a triangle that had a gap in the center.
And we reasoned that there were two possible outcomes
of the study.
Possibility one is that as empiricists and the then-very
influential child psychologist--
developmental psychologist Jean Piaget
argued, for a four-month-old infant who isn't yet
reaching for things, the world is
an array of visible fragments.
So they will see this thing as ending
at this edge where the occluder begins, and this display will
look more similar to them than this display,
so they'll be more interested in that one.
There was also the theory from Gestalt psychologists
and others that predicted the opposite, that there would
be automatic completion processes that
would lead any creature, whether they were experienced or not,
to perceive the simpler arrangement, which is this one.
Those, it seemed to us, were the only two options.
Baby research is really fun because it
can surprise you even when you think
you've covered all the bases.
Neither of those turned out to be true.
What happened instead was that when we took the occluder away,
you still saw an increase in looking
both to the connected object and to the separate object,
and those two increases were equal.
Now, this could have been for an extremely boring reason.
Maybe babies were only paying attention
to the thing that was closest to them in the array.
So we very quickly tested for that in the following way.
Instead of contrasting an array with a small gap to an array
that had it filled in, we contrasted an array
with a small gap to an array with a larger gap,
too large to have fit behind the occluder.
And there, babies looked longer at the array
with the larger gap.
So we know it's not that they're not
seeing this back form and its visible surfaces,
but they seem to be uncommitted as to whether those surfaces
are connected behind the occluder or not.
They don't see them as ending where the occluder begins,
but they don't clearly see them as connected, either.
And we showed that this was quite generally true,
both for simpler arrays and for more complicated-- well,
for richer ones, like a sphere.
We did this with a bunch of different arrays.
And under these conditions, where
the arrays are stationary, that's what we found.
But there was one condition where
we got a different finding, and that's
when we took one of these arrays and moved it
behind the occluder, never moving it enough to bring
the center into view, but moving it enough such
that the top and bottom were moving together.
And when we did that, now babies looked
longer at the display that had the gap.
That raised the question, why is motion having this effect?
And the immediate possibility, we thought,
is motion is calling their attention to the rod,
so they're tending to it more than they otherwise
would, and it's leading them to see its other properties,
like the alignment of its edges.
So to test that, we gave them misaligned objects differing
in color, differing in texture.
All of the edges-- none of the edges
were aligned with each other.
If motion was just calling attention to alignment,
it shouldn't do that in this case.
But in fact, we found that after getting bored with that,
infants expected something like this, not something like that.
They looked longer at the display with the gap.
So it looks like the motion is actually
providing the information for the connectedness,
and the alignment is not playing much of a role at all.
Now, what could be going on here?
This is the kind of thing I think
that Josh likes to call a suspicious coincidence, right?
That an infant is looking at this array,
and isn't it odd that we're seeing this--
I'm seeing the same pattern of motion
below the occluder as I'm seeing above it?
Now that could be two separate objects that
just happen to be moving together,
but that would be rather unlikely.
You're much more likely to see a pattern like that
if in fact there's a between it and it's just one object that's
in motion.
I think that's probably the right way
to think about what's going on in these experiments.
But if it is, notice that not all coincidences
that are suspicious for us are suspicious for infants.
For us, it's a suspicious coincidence
that this edge is aligned with that edge.
For infants, it's not.
I think this is a case where we can
see infants can be useful for thinking
about our own cognitive abilities
because they seem to share some of our picture of the world,
but not all of our picture of the world.
And that can be a hint as to how that picture gets put together
and how it's organized.
So what kind of motion?
We've tried a bunch of different ones.
One of them is vertical motion.
That's interesting because it's also a rigid displacement
or motion in depth.
They're both rigid displacements in three-dimensional space.
Actually, all of these three are.
But in this case, you don't get any side-to-side changes
in the visual field.
I think I animated this.
Yeah.
So this is kind of what the baby is seeing.
By the way, all of these studies were done with real 3D objects
and they had textures on them, and so forth.
They've also all since been replicated
in other labs using computer animated displays, which
we didn't have--
which weren't available back in the day.
And you get the same result. So I'm just
doing cartoon versions of them here,
but actually babies showed these effects
across a range of different displays.
So there's vertical motion.
Here is motion in depth.
Oh, and by the way, we're not restraining babies' heads,
so it's not going to be anything near as, like,
simple uniform as what's at their eye,
is what I'm showing here.
And then rotational motion, like that, around the midpoint.
And what we found is that babies used both vertical motion
and motion in depth about as well as they
used horizontal motion to perceive the connectedness
of the object.
They did not use rotary motion.
So I know there's a lot of interest and projects focused
on perceptual invariance.
And I think there's an interesting puzzle here,
and it's one that Molly is very interested in, in the work
that she's doing on geometry.
These are all rigid motions.
But somehow, rotation seems to be a whole lot harder
for young intelligent beings to wrap their heads around
than translation is--
including translation in depth or vertical translation.
There's something hard about orientation changes.
And in fact, I think they remain hard for us as adults.
If you think of things like how the shape of a square
seems to change if you rotate it 45 degrees so it's a diamond.
It's no longer obvious that it's got four right angles.
There's something about orientation that's
harder than these other things.
And I think we were seeing that here.
When an object-- when a baby is sitting still and a rod
is moving behind an occluder, it's
moving both relative to the baby and relative
to the surroundings, which of those things
matters to the baby?
So Phil Kellman did the ambitious experiment
of putting a baby in a movable chair
and moving the baby back and forth.
In one condition, the baby is looking at a stationary rod,
but his own motion is such that if you put a camera where
the baby's head is, you'll see the image of that rod moving
back and forth behind the block.
In the other condition, the motion of the rod
is tied to the motion of the baby,
so it's always staying in the middle of the baby's
visual field, but it's actually moving through the array.
And it turned out that it's--
OK, so whether the baby was still or moving
didn't matter at all.
So if the object is-- sorry, I did these wrong.
This should be still, that should be moving.
If the object is still, and whether the baby is still
or moving, it doesn't work.
If the object is moving--
the diagram is right.
It was just my label that's wrong.
If the object is moving, it doesn't
matter whether it's being displaced in the infant's
visual field or not.
It's seen as moving.
Now, this isn't magic.
The studies are not being done in a dark room
with a single luminous object where the baby wouldn't
be able to tell.
There's lots of surround-- it's in a puppet stage
and that is stationary.
So there's lots of information for the object moving
relative to its surroundings in all
of the conditions of this study, and I'm sure that's critical.
But for the point of view of the infant's connecting
of the visible ends of the object,
the question he's trying to answer
is, is that thing moving?
Not, am I experiencing movement in this changing scene?
Retinal movement.
So if it's the case that--
what those last findings suggest is
that the input representations to the system that's
forming objects out of arrays of visual surfaces
already capture a lot of the 3D spatial structure of the world.
This is a relatively late process.
And it allows us to ask, is it even specific to vision?
Would we see the same process at work
if we presented babies with the task of asking, am I feeling--
are two things that are moving in the world connected?
Or are they not, in areas that I'm not perceiving?
We can ask that in other modalities.
So we did a series of studies-- this is with Arlette Streri.
We did a series of studies looking at perception
of objects by active touch.
By taking four-month-old babies and putting a bib over them.
Now I said they can't reach for objects,
but if you put a ring in a baby's hand, even a newborn's
hand, they'll grasp it.
So we put rings in their two hands.
And in one condition, the rings were rigidly attached,
although the array was set up so that they couldn't actually
feel that attachment and they couldn't see anything,
about the object, anyway, because they
had the screen blocking them.
But as they moved one, the other would move rigidly with it.
In the other condition, the two were unconnected,
so they would move independently.
And after babies explored that for-- over a series of trials,
and as in the other studies, we then
presented visual arrays in alternation
where the two rings were connected or not.
And found that in the condition where they had moved rigidly
together, infants extrapolated a connection
and looked longer at the arrays that were not connected.
In the case where they moved independently,
they did the opposite.
Now, that doesn't tell us that there is
a single system at work here.
It could be that there are, as Shimon, I believe,
was saying yesterday afternoon, there
are redundancies in the system.
You have different systems that are
capturing the same property.
That's still true.
But here's a reason to--
we went on to ask not only what infants can do,
but what they can't do.
And I think it gives us reason to take seriously
the possibility that there's actually
a single system at work here.
What we did-- I haven't pictured it here--
is, instead of varying the motion of the things, we did
vary their motion, but we also varied their other properties.
So their rigidity.
We contrasted a ring that was made out
of wood with a ring that was made out
of some kind of spongy, foam-rubbery material--
their shape, their surface texture.
Asking, do infants take account of those properties
in extrapolating a connection?
Are they more likely to think two things
are connected to each other if they're both
made of foam rubber than if one of them
is made of foam rubber and the other is made of wood?
We never found any effect of those properties,
just as we didn't in the visual case.
So we see not only the same abilities, but the same limits.
And while that's not conclusive, I
think it adds weight to the idea that what
we could be studying here-- we started in the visual modality.
But what we could be studying here
is something that's more general and more abstract.
Basic notions about how objects behave that apply not only
when you're looking at things, but when you're actively--
when you're feeling them, actively manipulating them,
exploring them in other modalities.
So I put a question mark because it's not absolutely conclusive,
but I think we should take seriously that possibility.
OK.
Only motion.
Is motion the only thing that works?
Or will other changes work, so if an object changes in color?
We created a particularly exciting color change
by embedding colored lights within a glass rod
so it's flashing on and off.
Succeeded in eliciting very high interest in that array.
Babies looked at it for a long time,
but only the motion array was seen as connected
behind the occluder.
So it looks like not all changes elicit this perception.
It's an open question what the class of effective changes is.
Maybe it's broader than just motions,
but it doesn't seem like all changes work.
Finally, is motion the only variable
that influences infants' perception
of-- the only property of surfaces that influences
infants' perception of objects?
The answer to that seems to be no.
So we studied that in a different situation
for which this is just a very impoverished cartoon.
We took two block-like objects--
of different colors and textures in some studies,
same color and texture in others.
It didn't matter.
And put one on top of the other and either presented
them moving together or moving separately.
And then tested whether babies represented them as connected
in either of two ways.
Some of the studies were done with babies
who were old enough to reach.
And then we could ask, are they reaching for it
as if it were a single body or as if there
were two distinct bodies there?
I could give you more information about that
if you're interested.
The other was with looking time, where
we had a hand come out and grasp the top of the top object
and lift it.
And the question is, what should come with it?
Will the bottom object come with it as well
or will the top object on its own?
When the things had previously moved together,
they expected it all to move together.
When they'd moved separately, they
expected only the top object would move by itself.
And when there was no motion at all,
findings vary somewhat from one lab to another,
but mostly they tend to be ambiguous in the case where
there's no motion.
So there it looks like motion is doing all the work.
But if you make one simple change to this array
that you can't do in the occlusion studies,
you simply change the size of this object
and present it such that there's a gap between the two objects.
And you can either do it with this guy floating magically
in midair, or you can do it with two objects side
by side, both stably supported by a surface.
If there's a visible gap between them,
the motion no longer matters.
They will be treated as two distinct objects,
no matter what.
So what I think is going on here is
that babies have a system that's seeking
to find the connected, the solid connected bodies.
The bodies that are internally connected and will
remain so over motion.
And that's what's leading them to see
these patterns of relative motion or these visible gaps
as indicating a place where one object ends and the next object
begins.
I did want to get on to the problem of tracking objects
over time, perceiving not what's connected to what over space,
but what's connected to what over time.
Under what conditions are the thing that I'm seeing now
the same thing that I was seeing at some place
or time in the past?
So conceptually, it feels like continuity of motion over time
is related to connectedness of motion over space.
And it's been tested for in a variety of ways.
Here's one set of studies that we
did, where we have an object that moves behind
a single screen, and then either is-- and it starts here,
ends up here.
And either is seen to move between the two screens
or is not.
And we ask babies in effect, how many
objects do they think are in this display,
by boring half the babies with this,
half the babies with that, and then presenting them
in alternation with arrays of one
versus two objects, neither of which
ever passes through the center, but the arrays
differ in number.
In the one case, it's either moving over here
or it's moving over there on different trials.
And what we find is that in this case,
they expect to see one object and look longer at two.
In this case, they expect to see two objects
and look somewhat longer at one.
There's actually an overall preference for looking at two,
but you get that interaction and there's
a slight preference for looking at one in that condition.
Providing evidence, I think, that babies
are tracking objects over time by analyzing information
for the continuity of--
or discontinuity of their object motion.
Now, Lisa Feigenson has conducted
stronger tests of this, I think, with somewhat older babies.
When babies get older and they do more,
you can do stronger tests.
So these are babies who are old enough
to crawl, old enough to eat, and old enough
to like graham crackers.
So she puts the baby back here, and in one set of studies,
she takes a single graham cracker, puts it in one box,
and then takes two graham crackers, one at a time,
and puts them in the other box.
And then the baby, who's being restrained by a parent,
is let loose.
And the question is, which box will they go to?
And they go to the box with the two graham crackers.
My favorite study, though, in this whole series
was one that she and Susan Carey ran as a boring control
condition.
I think it's the most interesting of the findings,
though.
In the boring control condition, they
were worried about the fact that maybe babies are
going to the box with two because they
see a hand around that box for a longer period of time,
doing more interesting stuff.
So they did the following boring control.
The two condition was the same as before.
So a hand comes out with a single graham cracker,
puts it in the box, comes out empty,
takes a second graham cracker, returns with a second graham
cracker, puts it in the box.
In the other condition, the hand comes out
with one graham cracker, puts it in the box,
comes out again with the graham cracker,
and then goes back into the box with that graham cracker.
So you've got more graham cracker sightings on the left.
You've got a same amount of hand activity on the two sides,
but the babies go to the box with two.
They're tracking the graham crackers, not the graham
cracker visual encounters.
They're tracking a continuous object over time.
Finally, objects.
Scenes don't usually just contain
a single object that's either connected, continuously visible
or not, or connected or not.
They contain multiple objects and those objects interact
with each other.
Shimon talked yesterday afternoon about the evidence
that babies are sensitive to these interactions,
at least down to about six months of age in the conditions
he was talking about.
In slightly different conditions,
the sensitivity has been shown as young
as three months of age.
Basically, here's a paradigm that will show that,
if you have a single object that's moving toward a screen.
Another object is stationary behind the screen.
But at the right time, the time at which this object,
if it continued moving at the same rate, at the point
where it would contact that object,
this object starts to move in the same direction.
And now, after seeing that repeatedly,
the screen is taken away and babies either
see the first object contacting the second and the second one
immediately starting to move, or they
see the first object stopping short
of the second an appropriate gap in time,
and then the second object starts to move.
And they look longer at this display,
providing evidence that they inferred
that the first object contacted the second at the point
at which it started to move.
Interestingly, as in the case of the occluded object studies,
if instead of having the second object move,
you have it change color and make a sound,
so it undergoes a change in state, but no motion,
the babies no longer infer contact in this condition.
They are attentive to those events.
They watch them a lot, but they're
uncommitted as to whether that first
object-- this is work of Paul Muentener and Susan Carey
relatively recently.
It wasn't done with cylinders, it
was done with a toy car that hits a block,
I think, or doesn't hit the block.
They're uncommitted as to whether the car contacted
the second object or not, if the second object
changes state but doesn't move.
Returning to the case where they succeed--
namely, this thing went behind a screen, the other thing started
to move, infants inferred that they came into contact--
that begins to suggest that maybe babies have some notion
that objects are solid, that two things can't
be in the same place at the same time,
that when one moving thing hits another thing, one
or the other of them or both, their motion has to change,
because they're not going to simply interpenetrate
each other.
And Josh already very briefly pointed
to some very old studies suggesting that babies have--
make some assumption that objects are solid as early as--
I think in the earliest studies done
with babies it's about two and a half months of age.
These are these studies that Renee Baillargeon did
that start with simply a screen, a flat screen,
rotating on a table, rotating 180 degrees back and forth
on a table.
Then she places an object behind this wall.
The screen is lying on the table with its back edge
right here at the middle.
She places an object behind it, and then the screen
starts to rotate up around the back edge
and the question to the infants in effect is,
what should happen to that screen?
And the two options she presents to them
is it either gets to the point where it would contact
this object which is now fully out of view,
and stops, and then returns to its first position, which
is a novel motion, but consistent
with the existence, location, and solidity
of that hidden object.
Or it continues merrily on its way and the same pattern
of rotation as before.
When it does that, of course, it's
going to come back flat on the screen
and there's not going to be any object there.
If there had been an object, it would
have had to be compressed.
Or what I think actually went on in those studies,
it was quickly and surreptitiously knocked out
of the way.
And infants looked less at this event than at this one--
this one, sorry-- providing some evidence
that they were representing these objects, both as
existing when they were out of sight, and as solid.
So this is just a summary, not a claim about knowledge
development, about--
I'm attempting to characterize here
with motion over just one dimension of space and time,
how infants seem--
what infants seem to represent about the behavior of objects.
Namely that each object moves on a continuous path
through space and over time.
That it moves cohesively.
It doesn't split into pieces as it's moving.
So if you've seen something move like this,
then you find it unlikely that if this were lifted,
it would go on its own, and you look longer at that.
There is no merging, where two things that
previously moved independently now move together.
So after looking at this, it would also
be unlikely, if you lifted this, for the whole thing
to jump up at once.
They move without gaps.
They move without intersecting other objects
other objects on their paths of motion, such that two things
are in the same place at the same time.
And they move on contact with other objects
and not at a distance from them.
So that's just a summary of what I
think these studies show about four-month-old infants, not
newborns.
They also show that infants' perception of objects
is really limited.
There's all these situations under which we see unitary,
connected, bounded objects when they don't.
And interestingly, research by Fei Xu and Susan Carey
shows that even when you present really quite surprisingly
old infants, 10-month-olds, with objects that should be really
familiar to them, like toy ducks and trucks,
they don't assume that these two objects will be distinct
if they undergo no common motion.
If they're simply presented stationary,
the babies seem uncommitted as to whether there's
a boundary between them or not.
So they're using very limited information
to be making these basic--
building these basic representations
of what's connected to what, where one thing ends
and the next begins.
Now, this changes very abruptly between about 10
and 12 months of age.
They start treating those as two separate objects,
whether they're moving together or stationary or not.
Now, infants' tracking of objects
shows very similar limits.
So I told you they succeed in perceiving--
representing two distinct objects
in a situation like this.
But up until and including 10 months of age,
they fail in this situation.
If a truck comes out on one side of a single large screen,
so you're not getting information
for the motion behind that screen,
and a duck comes out on the other side,
and you ask babies, in effect, how many things are there?
One or two?
By removing the screen and alternately presenting
those two possibilities, they are uncommitted
between those two alternatives.
In this situation as in the previous one,
there's this very abrupt change between about 10
and 12 months of age.
And I can't resist saying, even though I'm way over time,
that Fei Xu has shown that that change is interestingly related
to the child's developing mastery of expressions
that name kinds of objects.
So she's been able to show, for example, that if you simply
ask for individual infants, when did they start succeeding here,
their success is predicted by their vocabulary
as reported by parents.
She's also shown that if you take a younger
infant who would be slated--
destined to fail this study, but as you bring objects
out on the two sides, either familiar ones or novel ones,
starting at about nine months of age,
if you name them and you give them distinct object names,
they now infer two objects.
And in fact, they'll even do it if the two
things you bring out from behind a single wide screen
look the same.
If you bring one thing out and say, look, a blicket,
and put it back in, and then bring something out and say,
look, a toma, even if it looks the same,
they'll infer two objects.
So there seems to be this change that's
occurring at the end of the first year
quite dramatically that's overcoming this basically meant
that we're seeing earlier on.