Permanence
[email protected]
objects
have boundaries
persist through time
causally interact
knowledge of objects
involves
segmenting them
representing them as perstising
tracking their causal interactions
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.
Spelke et al. (1995) 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)
They were then shown one of two test stimuli.
Spelke et al (1995, figure 3)
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} Baillargeon, 1987 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} Baillargeon, 1987 figure 2 \end{center}
source: Baillargeon et al (1987, figure 2)
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.’
(Sirois & Jackson, 2012, p. 73)
‘our use of a factorial design as opposed to collapsing rotation angle and
box in a single pair of test events clarifies the picture.’
(Sirois & Jackson, 2012, p. 74)
Sirois & Jackson 2012, figure 1
Things are rarely so straightforward.
Sirois and Jackson 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 Sirois and Jackson
did not find evidence for an ability to represent objects as persisting?
This certainly justifies caution in relying on any single experiment.
Taken alone, Baillargeon’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 Spelke & Hespos, 2001 or
Baillargeon, 2002).
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 Schöner & Thelen (2006); for critical
discussion of measures involving looking times generally, see
Aslin (2007).
}
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.
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)