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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.

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)?

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.