Lecture 04 | Origins of Mind (Warwick 2020)

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Origins of Mind : 04

[email protected]

question

The question for this course is ... We are going to approach this question by examining the evidence from developmental science, and identifying philosophical problems created by the evidence.

a challenge

A key challenge concerns the nature of mental states and actions in children who developing capacities to know simple facts about of the world. Last week I illustrated this by discussing knowledge of physical objects ...

plan

objects

causes

colours

words

non-verbal communications

minds

actions

When do humans first come to know facts about the locations of objects they are not perceiving?

look: by 4 months of age or earlier (Baillargeon 1987).

look: by around 2.5 months of age or earlier(Aguiar & Baillargeon 1999, Experiment 2)

search: not until after 7 months of age (Shinskey & Munakata 2001)

‘action demands are not the only cause of failures on occlusion tasks’

Shinskey (2012, p. 291)

‘the tip of an iceberg’ Charles & Rivera (2009, p. 994)

Suppose we ask, When do humans first come to know facts about the locations of objects they are not perceiving? Some evidence points to an early age, perhaps 2.5 months or earlier. But other evidence points to a much later age, 7 months at the earliest.

You might think, this is just an issue about measuring age. But I want to argue that it points to a deeper problem. The problem is how to characterise the mental states and actions of typically developing infants in their first months of life, when they can perform some actions for the reason that there is an object behind a screen but when this ability is strictly limited.

Uncomplicated Account of Knowledge

If I’m right, we need to rethink fundamental claims about mental states. These are coded in the Uncomplicated Account of Minds and Actions.

But faced with this, we should try to hold on to the Uncomplicated Account for as long as possible. There are two ways to do this.

One possibility is to insist that infants, despite failures to search, really can have beliefs about, and knowlegde of, the locations of unseen objects. For all we have seen so far, it might be that this is right. Perhaps, for example, there is something especially tricky about searching. Or perhaps there are other studies which show, contra Shinskey and Munakata, that four months olds really can search for unperceived objects. This deserves careful investigation.

Another possibility is to insist that infants, despite apparently demonstrating intelligent responses to unperceived objects in their looking behaviours, just can’t ever act for the reason that there is an object behind a screen. Their responses are not really intelligent but driven by some more basic process.

I want to consider this possibility first.

lots of evidence

We’re going to consider lots of evidence. The gist will be that we cannot reject the idea that infants just can’t ever act for the reason that there is an object behind a screen.

As you’ll see, different researchers have quite different theories. Why? I could just tell you what I think the balance of scientific evidence allows us to conclude. But I want you to learn to evaluate the scientific evidence for yourself. More importantly, there is uncertainty about what the balance of scientific evidence allows us to conclude. If you look at the research carefully, I thin you’ll find that no one yet has a fully adequate answer to the question, When do humans first come to know facts about the locations of objects they are not perceiving? So this question presents a significant challenge for us.

Three Abilities to Underpin Knowledge of Objects

\section{Three Abilities to Underpin Knowledge of Objects}

The question for this lecture concerns knowledge of physical objects. When do humans first come to know simple facts about particular physical objects? To illustrate, consider the fact that this telephone is located here, or the fact that this telephone is square. I take it that no one is born knowing any such facts. So there was a time when you knew no facts about particular physical objects at all, and then, sometime later, you came to know some such facts. How did you make this transition? How do humans first come to know facts about particular objects?

(For the rest of this lecture I'll drop the qualifier `physical' since this is all about physical objects as opposed to, say, abstract objects like numbers or forms.)

knowledge of physical objects

objects

have boundaries

persist through time

causally interact

[ducks picture] The way objects are ordinarily arranged in space, so that one occludes parts of another, prevents us from doing this in any simple way.

objects

have boundaries

persist through time

causally interact

knowledge of objects
involves

segmenting them

representing them as perstising

tracking their causal interactions

When Hannah hides behind the logs and a girl later pops up, we can ask whether it is Hannah again or another girl. That is, we know that objects can persist despite disappering from view---and despite becoming entirely imperceptible.

objects

have boundaries

persist through time

causally interact

knowledge of objects
involves

segmenting them

representing them as perstising

tracking their causal interactions

Objects causally interact with each other; one pan supports another, two people collide and bounce off each other. Relatedly, objects have counterfactual lives: sometimes you can say, truly, that if that barrier had not been there, the car would be at the bottom of the valley now.

objects

have boundaries

persist through time

causally interact

knowledge of objects
involves

segmenting them

representing them as perstising

tracking their causal interactions

the question

As mentioned, the question we'd like to answer is how humans first come to know any facts about particular physical objects. Before you know any such facts you live in something like a world of mere features. In this feature world, nothing persists and there are no causal interactions only patterns. And nothing exists except in your perceptual fields.

Now the question of how humans make this transition to knowing some facts about particular physical objects is too hard to face head on. But we can approach it by asking,

The question for this lecture is,

How do humans come to meet the three requirements on knowledge of objects?

Segmentation and the Principles of Object Perception

\section{Segmentation and the Principles of Object Perception}

How do humans segment objects?

first requirement: segmentation

Recall that the way objects are ordinarily arranged in space, so that one occludes parts of another, prevents us from doing this in any simple way.

Infants from 4.5 months of age can use featural information to segment objects.

using featural information

Needham (1998)

In Amy Needham's 1998 study, 4.5 months old infants were shown a display like this. Featural information---the difference in textures of the objects---suggests that these are two separate objects. But can infants use this information to detect that there are two objects?

Some infants were then shown the object being moved like this, so that it is clearly two separate objects.

Other infants where shown the object being moved like this. If infants think there is one object, they should expect the second kind of movement. But if infants think there are two objects---if, that is, they can use the featural information to segment objects---then they should expect the former kind of movement. What were the results? ...

Needham (1998, figure 4)

Needham's results are evidence that infants from 4.5 months of age can use featural information to segment objects.

method

violation-of-expectations

[I need to explain the method used in violation-of-expectations, and to compare it with the method of habituation.] A violation-of-expectations experiment involves a pair of events. Infants are divided into two groups; one group sees one event, the other sees the other event. (This is the between-subject version; it might also be done within subjects.) The experimenter measures how long the infants look at each event. Of interest is whether infants reliably look longer at one of the two events. If they do, this is interpreted as evidence that this event---the one infants reliably look longer at---is in some way interesting to them. And, if the events are well chosen, their interest indicates that the event violates an expectation they have. In the experiment we are considering, the expectation violated is the expectation that the two objects should move separately.

At this point you might well ask, What is an expectation? This is an important question but let me postpone it for now.

To return to Needham's experiment, interestingly, 4.5 month old infants were able to succeed even when the point of contact between the two objects was occluded, as in this diagram.

Needham (1998, figure 6)

These are the results for 4.5 month old infants.

One further thing: infants can also use shape information in segmenting objects, and shape information appears to trump featural information \citep{needham:1999_role}.

Needham (1998, figure 7)

Can we fully explain how infants segment objects just by appeal to features? To see why it couldn't be just features that we use to segment objects, consider some more cases ...

Could it all be features?

`infants perceive the boundaries of a partly hidden object by analyzing the movements of its surfaces: infants perceived a connected object when its ends moved in a common translation behind the occluder. Infants do not appear to perceive a connected object by analyzing the colors and forms of surfaces: they did not perceive a connected object when its visible parts were stationary, its color was homogeneous, its edges were aligned, and its shape was simple and regular' \citep{kellman:1983_perception}.

Here is an occluded object---a stick behind a box.

The movement is enough to convince 4-month-old infants that there is just one stick even though they never see its middle \citep{kellman:1983_perception}. We can discover this by measuring how different displayes cause them to dishabituate.

Spelke (1990, figure 2)

After being habituated to this this, 3-month-old infants were shown one of two displays.

Kellman & Spelke (1983, figure 3)

And here are the results (subjects were 3-month-old infants).

Kellman & Spelke (1983, figure 4)

The fact that infants can correctly segment partially occluded objects based on their movements already indicates that they can't be thinking about features only.

For more evidence, consider this display. The two parts of the moving object are featurally different. Despite this, infants expect to see a single connected object behind the block (\citealp{kellman:1983_perception}, Experiment 6; \citealp{Spelke:1990jn}).

Kellman & Spelke (1983, figure 13)

Here are the test stimuli (each groups is shown one or the other).

Kellman & Spelke (1983, figure 13)

And here are the results.

Subjects in this experiment were 4-month-old infants.

So we saw that infants can use featural information to segment objects, but the principle of cohension can trump featural indicators of difference.

So infants' abilities to segment objects are not based entirely on recognising features.

Kellman & Spelke (1983, figure 14)

If infants do not rely only on features to do this, then how do infants segment the objects in the displays we've just been seeing?

If not by features, then how? Principles!\citet{Spelke:1990jn} suggests that infants rely on a set of principles to segment objects. But what are the principles?

Recall this diplay with on object moving behind a stationary block. What kind of principle could be used to identify that the occluded thing is a single object?

Kellman & Spelke (1983, figure 13)

rigidity—‘objects are interpreted as moving rigidly if such an interpretation exists’

\citet{Spelke:1990jn} suggests the principle of rigidity. This principle says that ‘objects are interpreted as moving rigidly if such an interpretation exists’ The hypothesis that this principle describes in part how infants segment objects correctly predicts that they will treat the moving occluded stick as a single object.

But rigidity is not the only principle we need to explain how infants segment objects ...

What justifies us in supposing that a rigidly moving object needs to be joined up?

... to answer this question, consider the Principle of Cohension

cohesion—‘two surface points lie on the same object only if the points are linked by a path of connected surface points’

(Spelke 1990)

cohesion:

‘two surface points lie on the same object only if the points are linked by a path of connected surface points’

(Spelke 1990)

Another principle which seems to be involved in segmenting objects is the principle of cohension. According to this principle, ‘two surface points lie on the same object only if the points are linked by a path of connected surface points’ \citep{Spelke:1990jn}.

Spelke (1990, figure 4)

For example, objects arranged as on your left were percevied by 3-month-olds as two objects, whereas infants treated the displays like that on your right as if they were one object. (This was measured using a habituation paradigm \citep{kestenbaum:1987_perception}. Infants were habituated to the display. Then either one object's position changed, or both objects' positions changed but in such a way as to preserve the overall configuration of the two objects. Infants could show that they perceived the configuration as a single object by looking longer when just one object's position changed.)

Here's a second example using moving rather than static stimuli and a different method: reaching rather than looking. Let me explain the stimuli first.

How does the principle of cohension apply to this moving display? As we just formulated it, it doesn't seem to. After all, in both cases all points on the stimuli are lnked by a path of connected surface points. However, the principle should be read as saying more implying that: ‘When two surfaces are separated by a spatial gap (as in Figure 4a) or undergo relative motions that alter the adjacency relations among points at their border (as in Figure 4i), the surfaces lie on distinct objects’ \citep[p.\ 49]{Spelke:1990jn}.

The question is, Do infants segment these objects in accordance with the Principle of Cohesion? \citet[Experiment 2]{spelke:1989_reaching} used a reaching experiment with 5-month-old infants. The smaller of the two objects was always closer to the infants. Infants should reach more often for the smaller, nearer object when they represent the simuli as two separate objects than when they represent it as a single object. (This is not obvious, but the researchers do justify this claim carefully \citep[p.\ 186]{spelke:1989_reaching}.) So the idea is that by comparing how often 5-month-olds reach for the smaller object, we can see whether they treat it as a separate object in one case but not the other. To make this vivid, let me show you their apparatus ...

Spelke et al 1989 figure 1.

Here you can see the infant sitting in front of the two objects which could be made to move together or separately.

Spelke et al 1989 table 2.

And here are the results. You don't need to read the table, I put it here just to mention that this is a within-subject design.

[*explain within- vs between-subject].

Overall, infants reached to the smaller, top object more often when they moved in opposite directions than when they moved together. Given the background assumption, this is evidence that infants segmented the objects differently depending on their motions, and did so in just the way that adults would \citep[Experiment 2]{spelke:1989_reaching}.

\citet{Spelke:1990jn} proposes that our ability to segment objects depends on four principles. We've already seen two of these in action (rigidy and cohesion), and we will shortly see that a further principle is needed, too.

Principles of Object Perception

\textbf{Principles of Object Perception \citep{Spelke:1990jn}}

cohesion—‘two surface points lie on the same object only if the points are linked by a path of connected surface points’
boundedness—‘two surface points lie on distinct objects only if no path of connected surface points links them’
rigidity—‘objects are interpreted as moving rigidly if such an interpretation exists’
no action at a distance—‘separated objects are interpreted as moving independently of one another if such an interpretation exists’

(Spelke 1990)

We've already seen this principle in action.

Boundedness is just the converse of cohesion. Strictly speaking, cohension allows us to infer that we have two distinct objects, but not to infer that we have a single object---for that, we need boundedness. So when I was talking a moment ago about the Principle of Cohesion, strictly speaking I was also appealing to the Principle of Boundedness.

We saw an example of the principle of rigidity in action earlier, with the moving stick experiment.

The final Principle, no action at a distance, is a converse to rigidity.

I don't want to obsess too much about the details of these principles. It isn't important that there are exactly four, nor are their precise formulations. (Surely the principles as stated here are not exactly the principles we need to characterise how infants segment objects.) What I want us to focus on is just the fact that we can use a small number of principles to characterise how infants segment objects in a way that generates testable predictions, and these principles have been confirmed. This motivates us to ask ...

What is the status of these principles?

Spelke’s position might be put like this:

\begin{enumerate} \item We (as perceivers) start with a cross-modal representation of three-dimensional perceptual features which includes their locations and trajectories. \item Our task is to get from these representations of features to representations of objects. \item \emph{Descriptive component} We do this as if in accordance with certain principles (cohesion, boundedness, rigidity, and no action at a distance). \item \emph{Explanatory component} We acquire representations of objects because we apply the principles to representations of features and draw appropriate inferences. \end{enumerate}

The key point for our purposes is the explanatory component. The principles are not supposed to be merely heuristics for describing and predicting infants’ performance on preferential looking tasks. Rather, these principles are supposed to explain why infants look longer at some things than at others. This what motivates the hypothesis that infants know these principles and use them in reasoning about objects: unless this hypothesis is true, it’s hard to understand how the principles could have explanatory relevance.

1. How do four-month-old infants model physical objects?

2. What is the relation between the model and the infants?

3. What is the relation between the model and the things modelled (physical objects)?

The conjecture that someone can segment and represent physical objects does not by itself generate readily testable predictions. Everything depends on which model of physical objects characterises her phyiscal cognition.

So we should ask ...

1. How do four-month-old infants model physical objects?

In asking how infants model physical objects, we are seeking to understand not how physical objects in fact are but how they appear from the point of view of an individual or system.

The model need not be thought of as something used by the system: it is a tool the theorist uses in describing what the system is for and broadly how it works. This therefore leads us to a second question ...

2. What is the relation between the model and the infants?

3. What is the relation between the model and the things modelled (physical objects)?

Marr & Chomsky

The Simple View is inspired by two famous cognitive scientists, Marr and Chomsky. Marr showed that many visual processes can be described as inferences. And Chomsky pioneered the idea that humans’ knowledge of language depends on their knowing of a small number of principles. Similarly, Spelke’s suggestion is that human infants (and adults) come to know facts about particular physical objects by virtue of making inferences from a small number of principles which they know or believe.

What unites these three cases, Spelke on object segmentation, Marr on vision and Chomsky on syntax? It’s that they are straightforwardly cognitivist in appeal to knowledge and inference. Principles are known, and they are used via a process of inference. (There’s a nice quote from Fodor underlining this point.)

‘... the vocabulary in which Chomsky frames linguistic issues is explicitly epistemological. Thus, the grammar of a language specifies what its speaker/hearers have to know ... and the goal of the child’s language acquisition process is to construct a theory of the language that correctly expresses this grammatical knowledge.’

Fodor 2000, p. 11

‘Chomsky’s nativism is primarily a thesis about knowledge and belief; it aligns problems in the theory of language with those in the theory of knowledge. Indeed, as often as not, the vocabulary in which Chomsky frames linguistic issues is explicitly epistemological. Thus, the grammar of a language specifies what its speaker/hearers have to know qua speakers and hearers; and the goal of the child’s language acquisition process is to construct a theory of the language that correctly expresses this grammatical knowledge.’

\citep[p.\ 11]{Fodor:2000cj}

the simple view

So what is the status of Spelke’s principles of object perception? Consider what I shall call the Simple View ...

\textit{The simple view} The principles of object perception are things that we know or believe, and we generate expectations from these principles by a process of inference.

The simple view is that the Spelke principles are just known in whatever sense anything is known or believed. (We can't say the principles are known because strictly speaking they are not truths but only heuristics.) The simple view isn’t exactly Spelke’s, but it’s a useful starting point for discussion.

The Simple View is worth considering in its own right because it is so, well, simple. But our interest in it may be piqued by the fact that Spelke herself appears to have accepted the Simple View at one point in her thinking:

‘objects are conceived: Humans come to know about an object’s unity, boundaries, and persistence in ways like those by which we come to know about its material composition or its market value’

\citep[p.\ 198]{Spelke:1988xc}.

Spelke (1988, p. 198)

Now you might think that the case for these principles is not yet very strong. In that case, asking hard questions about their status would hardly be necessary. So let’s consider further evidence for these principles. We can do this by turning from segmentation (which was our first requirement on knowledge of objects) to representing objects as permanent.

Uncomplicated Account of Knowledge

So I’m arguing that infants act for reasons which involve particular physical objects well before they are 7 months old. This is what is pushing us in the direction of ascribing beliefs about those objects to the infants.

Permanence

\section{Permanence}

objects

have boundaries

persist through time

causally interact

knowledge of objects
involves

segmenting them

representing them as perstising

tracking their causal interactions

[*TODO*] Integrate converging findings on anticipatory (predictive) looking \citep{rosander:2004_infants}: `The obtained results are in general agreement with the numerous habituation studies that have investigated infants' emerging ability to represent temporarily occluded moving objects. The individual data show that 9–12-week-old infants begin to predict the reappearance of the object towards the end of the centrally occluded trials.'

[*TODO*] integrate this on reaching: \citep{vanwermeskerken:2011_anticipatory} (Interpretation is a bit out there, but it nicely illustrates how occlusion duration can affect reaching at around 7 months of age.)

[*TODO*] integrate this ERP measure of permanence: \citep{kaufman:2005_oscillatory}

\textit{Object permanence}:

Object permanence:

the ability to know things about, or represent, objects you aren't currently perceiving.

Permanence is a matter of living in a world where things don't go out of existence when unperceived.

You may not be perceiving your keys now, but there is a fact of the matter about where they are and you know this. (If not where they are, then at least you know that there is a fact about where they are.)

‘young infants’ physical world, like adults’, includes both visible [perceived] and hidden objects’

(Wang et al 2004, p. 194)

Although segmentation and permanence are conceptually distinct, they are closely related because movement is a clue to segmentation and movement sometimes invovles occlusion.

This becomes evident if we think about one more principle of object perception, the principle of continuity.

principle of continuity---

an object traces exactly one connected path over space and time

\emph{Principle of continuity} An object traces exactly one connected path over space and time \citep[p.\ 113]{spelke:1995_spatiotemporal}.

We easily understand this principle by considering cases that accord with, and violate, it.

Here is motion in accord with it.

Spelke et al (1995, figure 1)

Here is one violation of continuity.

And here is another violation of continuity.

\citet{spelke:1995_spatiotemporal} tested sensitivity to the principle of continuity in 4-month-old infants.

The infants were habituated to one of two displays.

Spelke et al (1995, figure 2)

Now in the continuous event we should perceive one object whereas in the discontinous event we should perceive two objects. But is this about segmentation or persistence? Segmentation since it's about distinguishing one object from another; and persistence since it's about representing temporarily unperceived objects.

They were then shown one of two test stimuli.

The measure was the degree of dishabituation as measured by looking time.

Spelke et al (1995, figure 3)

What's beautiful about these results is that the two groups show opposite patterns of dishabituation.

Recall that the continuity principle could be violated in two ways.

We've just seen a `continuity violation'. Next I want to show you a solidity violation.

Further evidence that infants represent unperceived objects from around four months includes Baillargeon's famous drawbridge study.

These are the test events from Experiment 1 of Baillargeon et al's 1987 study.

\begin{center} \citealp{baillargeon:1987_object} figure 1 \end{center}

Baillargeon et al (1987, figure 1)

'The habituation event was exactly the same as the impossible event, except that the yellow box was absent.' (Baillargeon et al 1985, 200)

These are the results from Experiment 1 of Baillargeon et al's 1987 study.

\begin{center} \citealp{baillargeon:1987_object} figure 2 \end{center}

source: Baillargeon et al (1987, figure 2)

I'm presenting this experiment as showing that infants represent objects as persisting, and do so in accordance with the Principle of Continuity. However, the experiment is also about causal interactions between objects. After all, infants are demonstrating sensitivity to the fact that a solid object must stop the drawbridge from rotating all the way back.

fail?

Some have been critical of the methods used in this experiment.

Sirois & Jackson 2012, figure 3

‘The lack of interaction between rotation angle and presence of a box in the looking time data is inconsistent with the suggestion of object permanence in our sample.’ \citep[p.~73]{sirois:2012_pupil}

‘our use of a factorial design as opposed to collapsing rotation angle and box in a single pair of test events clarifies the picture.’ \citep[p.~74]{sirois:2012_pupil}

So Baillargeon’s drawbridge study doesn’t demonstrate object permanence?

Sirois & Jackson 2012, figure 1

Things are rarely so straightforward. \citeauthor{sirois:2012_pupil} used computer generated stimuli whereas Baillargeon had a physical set-up, they studied 10-month-olds rather than 4-month-olds, and they used a different method (‘ children were ... not habituated by the time testing began’). So what can we conclude from the fact that \citeauthor{sirois:2012_pupil} did not find evidence for an ability to represent objects as persisting? This certainly justifies caution in relying on any single experiment. Taken alone, \citeauthor{baillargeon:1987_object}’s (\citeyear{baillargeon:1987_object}) studies are inspiring but not fully convincing. However many further experiments involving different groups of researchers, different scenarios and different methods provide converging evidence for the same conclusion: even four-month-olds can represent objects as persisting (for reviews see \citealp{Spelke:2001pg} or \citealp{Baillargeon:2002hb}). The initial, groundbreaking studies are probably methodologically imperfect, but the balance of evidence from subsequent experiments suggests that the discovery they illuminate is probably real.% \footnote{ For an opposing view see \citet{schoner:2006_using}; for critical discussion of measures involving looking times generally, see \citet{aslin:2007_whats}. }

Whatever your views on this experiment, not everything hangs on it. Fortunately there are at least a hundred further experiments which provide evidence pointing in the same direction. Here we'll look at just one more experiment.

Here is another way of demonstrating object permanence.

This experiment will suggest, incidentally, that the principles we have seen---continuity, rigidity and the rest---don't fully explain how infants succeed in representing objects as persisting.

The subjects were 4 month old infants.

They were shown a large object disappearing inside a small conatiner, or behind a narrow screen.

Wang et al (2004, figure 1)

The experiment was very simple.

All the experimenters did was measure how long infants looked in at the two events.

Infants looked longer at the narrow-occulder event.

Wang et al (2004, figure 2)

There was also a control condition.

In the control condition, infants saw a small rather than a large object.

Control condition

Wang et al (2004, figure 1)

Here’s the experimental condition again for comparison.

Experimental condition

Wang et al (2004, figure 1)

And here's the control condition again.

Control condition

Wang et al (2004, figure 1)

As you can see, there was a difference in looking times only in the experimental condition.

Wang et al (2004, figure 2)

By the way, this experiment is interesting partly because it doesn't use habituation, as Baillargeon's earlier drawbridge experiment did. It is also hard to explain the result by appeal only to the Principle of Object Perception that we have so far listed.

Lots of converging evidence for persistence ...

4- and 5-month-olds can track briefly occluded objects

scenario method source
1 vs 2 objects habituation Spelke et al 1995
one unperceived object constrains another’s movement habituation Baillargeon 1987
where did I hide it? violation-of-expectations Wilcox et al 1996
wide objects can’t disappear behind a narrow occluder violation-of-expectations Wang et al 2004
when and where will it reappear? anticipatory looking Rosander et al 2004

scenario	method	source
1 vs 2 objects	habituation	Spelke et al 1995
one unperceived object constrains another’s movement	habituation	Baillargeon 1987
where did I hide it?	violation-of-expectations	Wilcox et al 1996
wide objects can’t disappear behind a narrow occluder	violation-of-expectations	Wang et al 2004
when and where will it reappear?	anticipatory looking	Rosander et al 2004

We're considering abilities to represent objects as persisting even when not perceived. Where are we? We've seen that characteristing these abilities in terms of Principles of Object Perception enables us to make testable predictions, many of which have been confirmed. Importantly, we made the same claim about these Principles for abilities to segment objects. The abilities to segment objects and to represent them as persisting are conceptually distinct. However it may be that beliefs about a single set of principles underlies both abilities. This is one of Spelke's brilliant insights.

Where does this leave us? We still want to know about the status of the principles of object perception. As I said before, it is one thing to say they are descriptively adequate and another thing to understand how the Princples relate to cognitive mechanisms (processes and representations). But now the question about the status of these Principles is more pressing because the claim that these principles of object perception explain infants' (and adults', and other primates') performance is now harder to reject. It's harder to reject because we have converging evidence for the psychological reality of the principles from both segmentation and permanence.

principles of object perception

{

segmentation

permanence

... (?)

1. How do four-month-old infants model physical objects?

2. What is the relation between the model and the infants?

3. What is the relation between the model and the things modelled (physical objects)?

On the status of the Principles, consider this claim about the interpretation of the results of a violation-of-expectation experiment:

‘evidence that infants look reliably longer at the unexpected than at the expected event is taken to indicate that they (1) possess the expectation under investigation; (2) detect the violation in the unexpected event; and (3) are surprised by this violation. The term surprise is used here simply as a short-hand descriptor, to denote a state of heightened attention or interest caused by an expectation violation.’ \citep[p.\ 168]{wang:2004_young}

‘evidence that infants look reliably longer at the unexpected than at the expected event is taken to indicate that they

‘(1) possess the expectation under investigation;

‘(2) detect the violation in the unexpected event; and

‘(3) are surprised by this violation.’

(Wang et al 2004, p. 168)

What does ‘surprise’ mean here?

So this is not surprise in a sense that requires awareness of a change in one's own beliefs. It is rather that there is a particular way in which the detection of the violation is manifested.

Note that we are talking about expectations. This raises two questions: How do we arrive at these expectations? and What is an expectation? Spelke's claim is that we arrive at these expectations by inference from the Principles of Object Perception, including the principle of contintuity. So what is an expectation? On the simple view we are adopting for now, an expectation is just a belief. The attraction of this simple view is it allows us to take literally the claim that we know the principles of object perception and arrive at expectations by a process of inference.

Here is an illustration of the Simple View ...

‘To make sense of such results [i.e. the results from violation-of-expectation tasks], we … must assume that infants, like older learners, formulate … hypotheses about physical events and revise and elaborate these hypotheses in light of additional input.’

\citep[p.\ 329]{Aguiar:2002ob}

(Aguiar and Baillargeon 2002: 329).

So infants formulate hypotheses

And infants revise and elaborate these hypotheses in light of additional input. Now you might suggest that these researchers in talking about formulating and revising hypotheses do not mean to suggest that infants are doing this in the sense that you or I might, and so do not mean to imply that they have beliefs or knowledge. But ...

... they explicitly specify that infants do this ‘like older learners’.

So our current working hypothesis about the Principles is the Simple View. But before we go any further, let me say a little more about the third thing on our list, causal interactions ...

principles of object perception

{

segmentation

permanence

... (?)

We are far from fully understanding how humans are first able to represent objects as persisting. However, the fact that the ability appears so early in development entails that it does not demand language, nor much conceptual sophistication. This view is supported by the fact that the ability to represent objects as persisting is found in a wide variety of nonhuman animal including monkeys \citep{santos:2006_cotton-top}, lemurs \citep{deppe:2009_object}, dogs \citep{kundey:2010_domesticated}, % replication of Baillargeon’s drawbridge with dogs wolves \citep{fiset:2013_object}, %this is actually dogs and wolves cats \citep{triana:1981_object}, crows \citep{hoffmann:2011_ontogeny}, chicks \citep{chiandetti:2011_chicks_op}, and dolphins \citep{jaakkola:2010_what}.% \footnote{ If you read these studies you will find that some of the authors talk about Piaget's stages of object permanence, and about visible and invisible displacements. For our purposes few of these details matter; % $glossary:object permanence the main thing you need to know is just that having \emph{\index{$object permanence$}object permanence} is being able to represent objects as persisting even when they are briefly hidden from your view. } It is possible that humans’ abilities to represent objects as persisting are unrelated to some or all of these animals’, of course. Nevertheless, the fact that chicks can represent objects as persisting does show that doing this is not necessary something that requires much cognitive effort or conceptual sophistication.

Object permanence is found in nonhuman animals including

\begin{enumerate}

monkeys (Santos et al 2006)
\item monkeys \citep{santos:2006_cotton-top}
lemurs (Deppe et al 2009)
\item lemurs \citep{deppe:2009_object}
crows (Hoffmann et al 2011)
\item crows \citep{hoffmann:2011_ontogeny}
dogs and wolves (Fiset et al 2013)
\item dogs and wolves \citep{fiset:2013_object}
cats (Triana & Pasnak 1981)
\item cats \citep{triana:1981_object}
chicks (Chiandetti et al 2011)
\item chicks \citep{chiandetti:2011_chicks_op}
dolphins (Jaakkola et al 2010)
\item dolphins \citep{jaakkola:2010_what}
...

\item ...

\end{enumerate}

(Wolves matter because their performing similarly to dogs that show dogs' performance probably isn't a consequence of domestication, as \citet{fiset:2013_object} argue.)

Most of these animals have been tested using search as the measure, rather than looking times. (This will be important later.)

Note also that many of these studies contrast visible with invisible displacements, or talk about Piaget's stages of object permanence. For simplicity, that's not something I'm covering.

[Aside] Comparative research is hard.

‘The real difficulty is that there is no reward for the great majority of cats in retrieving an unmoving, silent, odor-free, covered-up object from which their attention has been distracted, and hence the cats will not show that they know where it is.’

(Triana & Pasnak 1981, p. 138)

Causal Interactions

\section{Causal Interactions}

objects

have boundaries

persist through time

causally interact

knowledge of objects
involves

segmenting them

representing them as perstising

tracking their causal interactions

The third requirement on knowledge of objects is an ability to track objects through causal interactions.

Here we're interested in very simple causal interactions, such as the collision of two balls or the interaction of a ball with a barrier.

Consider this case where a ball falls and lands on a bench. Suppose that there was a barrier in front of the bench, like the dotted line. Because the bench protrudes from the barrier, you could easily see where the ball will land. But of course you can only see this if you know that barriers stop solid balls. Spelke used this observation to provide evidence that 4-month-old infants can track objects' causal interactions.

Spelke et al 1992, figure 2

Infants were habituated to a display in which a ball fell behind a screen, the screen came forwards and the ball was revealed to be on the ground, just where you'd expect it to be. After habituation infants were shown one of two displays. Infants in the 'consistent group' were shown this.

Whereas infants in the 'inconsistent group' were shown this.

What should we predict? If infants were only paying attention to the shapes and ignoring properties like solid, they should have dishabituated more to the consistent than to the inconsistent stimlus. After all, that stimlus is more different from the habituation stimulus in terms of the surfaces. But if infants were are to track some simple causal interactions, then they might dishabituate to the 'inconsistent' stimulus more than to the 'consistent' stimulus because that one involves an apparent violation of a physical laws.

Here are the results.

(Recall that the subjects are 4-month-old infants.)

Spelke et al 1992, figure 3

This is evidence that infants can track causal interactions among objects, even when those causal interactions are occluded.

Chimpanzees also understand something of phyiscal interactions insofar as their looking times show sensitivity to support relations \citep{cacchione:2004_recognizing}.

Cacchione & Krist 2004, figure 2

Here are the results.

Cacchione & Krist 2004, figure 3

Lots of studies like this have been done with infants in their first six months of life.

Dogs can do this too.

This experiment used a search measure rather than a looking time measure.

Dogs had to retrieve a treat. The right location to search depended on whether the barrier was present or absent.

Kundey et al 2010, figure 1

The results show brilliant performance.

'Dogs correctly searched the near location when the barrier was present and the far location when the barrier was absent. They displayed this behavior from the first trial' \citep{kundey:2010_domesticated} (from the abstract).

Kundey et al 2010, figure 2

How do infants, adult humans and nonhumans track causal interactions among objects (including causal relations like support)?

Spelke suggests that the principles of object perception can explain this.

how?

For example, the position of an object falling onto a bench is predicted by the principle of continuity mentioned earlier.

\emph{Principle of continuity} An object traces exactly one connected path over space and time \citep[p.\ 113]{spelke:1995_spatiotemporal}.

Spelke et al (1995, figure 1)

(The other principles of object perception are on your handout.)

Spelke et al 1992, figure 2

Spelke et al (1995, figure 1)

This is Spelke's brilliant insight.

‘object perception reflects basic constraints on the motions of physical bodies …’

(Spelke 1990: 51)

\citep[p.\ 51]{Spelke:1990jn}

‘A single system of knowledge … appears to underlie object perception and physical reasoning’

\citep[p.\ 175]{Carey:1994bh}

(Carey and Spelke 1994: 175)

I think there's something here that should be uncontroversial, and something that's more controversial.

But first let me recap ...

Recap and Questions

\section{Recap and Questions}

As I said at the start, knowledge of objects depends on abilities to (i) segment objects, (ii) represent them as persisting and (iii) track their interactions.

\emph{Question 1} How do humans come to meet the three requirements on knowledge of objects?

Until quite recently it was held, following Piaget and others, that these three abilities appeared relatively late in development.

However, as we saw last week, more recent investigations provide strong evidence that all three abilities are present in humans from around four months of age or earlier.

Infants' looking behaviours indicate that they have expectations concerning segmentation, persistence and causal interactions.

\emph{Discovery 1} Infants manfiest all three abilities from around four months of age or earlier.

Three requirements

segment objects
represent objects as persisting (‘permanence’)
track objects’ interactions

The second discovery concerned how infants meet these three requirements this.

Principles of Object Perception

cohesion—‘two surface points lie on the same object only if the points are linked by a path of connected surface points’
boundedness—‘two surface points lie on distinct objects only if no path of connected surface points links them’
rigidity—‘objects are interpreted as moving rigidly if such an interpretation exists’
no action at a distance—‘separated objects are interpreted as moving independently of one another if such an interpretation exists’

Spelke, 1990

We've seen that infants' abilities to segement objects, represent them as persisting and track their causal interactions can be described by appeal to a single set of principles, the principles of cohension, boundedness, rigidity and no action at a distance.

This suggests that

\emph{Discovery 2} Although abilities to segment objects, to represent them as persisting through occlusion and to track their causal interactions are conceptually distinct, they may all be consequences of a single mechanism (in humans and perhaps in other animals).

Spelke suggests, further, that these principles of object perception explain infants' looking behaviours.

This means we must ask

\emph{Question 2} What is the relation between the principles of object perception and infants’ looking behaviours?

three requirements, one set of principles

three requirements, one set of principles: this suggests us that infants’ capacities are characterised by a model of the physical.

1. How do four-month-old infants model physical objects?

2. What is the relation between the model and the infants?

3. What is the relation between the model and the things modelled (physical objects)?

formal adequacy:

Let's suppose that Spelke is right that the principles are \emph{formally adequate}. That is, someone who knew the principles and had unlimited cognitive resources could use the principles to infer the track physical objects through simple causal interactions like those we've been considering. (So formal adequacy is a question of what is possible in principle.) I don't think we should question this.

descriptive adequacy

I also want to allow that Spelke's principles are \emph{descriptively adeqaute}. That is, they successfully describe how infants, adults and nonhumans deal with various situations. We can think of this in terms of \emph{as if}: it is as if these individuals are using the principles. But we have yet to come to what really matters to Spelke and to us. For accepting formal and descriptive adequacy is consistent with denying that Carey and Spelke's claim that ‘A single system of knowledge … appears to [does] underlie object perception and physical reasoning’ \citep[p.\ 175]{Carey:1994bh}.

That's because formal and descriptive adequacy leave open the question of what mechanisms are involved in tracking physical objects' causal interactions.

mechansim: Finally, we might claim that these principles are realised in the cognitive mechansisms invovled in object tracking. It just here that we have to face the second question, What is the relation between the principles of object perception and infants’ looking behaviours?. (e.g. the simple view) In answer to Q2, I suggested that we start with the simple view. The \emph{simple view} is the view that the principles of object perception are things that we know or believe, and we generate expectations from these principles by a process of inference. The attraction of the Simple View is that it promises to explain infants' sensitivity to objects' boundaries, their persistence and their causal interactions as manifested in a variety of looking behaviours. But, as we're about to see, the Simple View is completely wrong.

Keyboard Shortcuts?

Three Abilities to Underpin Knowledge of Objects

Segmentation and the Principles of Object Perception

Permanence

Causal Interactions

Recap and Questions

Keyboard Shortcuts`?`