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have boundaries

persist through time

causally interact

knowledge of objects

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.


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

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




... (?)

Three Questions

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.’

‘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.’

(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, , 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




... (?)

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

  • 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 ...
(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)