Object Indexes and the Principles of Object Perception

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This is a lecture about the origins of our knowledge of causal interactions, but I want to return to the topic of objects and the problem we encountered in the last lecture.

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

Three requirements

segment objects
represent objects as persisting
track objects’ interactions

When we asked how infants meet these three requirements, we found that a single set of principles, the Principles of Object Perception, seemed to underlie all three abilities.

Principles of Object Perception

cohesion
boundedness
rigidity
no action at a distance

(Spelke 1990)

We were then led to the question, What is the status of these principles? It's one thing to say that they describe how infants perform; but what we want is some understanding of the mechanisms.

the Simple View

The Simple View is one way to get a mechanism out of the principles. Recall that the \emph{simple view} is the view that the principles of object perception are things that we know, and we generate expectations from these principles by a process of inference..

Unfortunately, as we saw, the Simple View is wrong. We know it is wrong because it makes systematically incorrect predictions about infants' actions. These arise from a discrepancy between measures that involve looking times or eye movements and measures that involve other kinds of action, such as searching and pulling.

At the end of the last lecture (on objects), I said that the failure of the Simple View leaves us with a problem. We are now, at least, in a position to take a step towards solving that problem.

The principles of object perception

are not items of knowledge

instead

they characterise the operation of

object-indexes (aka FINSTs, mid-level object files)

Their upshot is not knowledge about particular objects and their movements but rather a perceptual representation involving an object index.

Leslie et al (1989); Scholl and Leslie (1999); Carey and Xu (2001)

\citep{Leslie:1998zk,Scholl:1999mi,Carey:2001ue}.

This amazing discovery is going to take us a while to fully digest. As a first step, note its significance for Davidson's challenge about characterising what is going on in the head of the child who has a few words, or even no words.

We saw this quote in the first lecture ...

‘if you want to describe what is going on in the head of the child when it has a few words which it utters in appropriate situations, you will fail for lack of the right sort of words of your own.

‘We have many vocabularies for describing nature when we regard it as mindless, and we have a mentalistic vocabulary for describing thought and intentional action; what we lack is a way of describing what is in between’

(Davidson 1999, p. 11)

The discovery that the principles of object perception characterise the operation of object-indexes doesn't mean we have met the challenge exactly. We haven't found a way of describing the processes and representations that underpin infants' abilities to deal with objects and causes. However, we have reduced the problem of doing this to the problem of characterising how some perceptual mechanisms work. And this shows, importantly, that understanding infants' minds is not something different from understanding adults' minds, contrary to what Davidson assumes. The problem is not that their cognition is half-formed or in an intermediate state. The problem is just that understanding perception requires science and not just intuition.

Return to this amazing discovery.

The principles of object perception

are not items of knowledge

instead

they characterise the operation of

object-indexes (aka FINSTs, mid-level object files)

Leslie et al (1989); Scholl and Leslie (1999); Carey and Xu (2001)

Let me make some more points about it.

First, it doesn't fully answer our question about the relation between the Principles of Object Perception and mechanisms in infants. It tells us that the Principles characterise a certain kind of perceptual process. This is progress; but we can still ask about the nature of the procesess and representations involved. This will become important when we consider knowledge in other domains.

Second, we haven't fully explained the discrepancy between looking and action-based measures for representing objects as persisting and tracking their causal interactions. After all, why do these perceptual representations of objects--the object indexes--not guide purposive actions like reaching and pulling? This is an issue we shall return to.

Third, it leaves us with a question we didn't have before. What is the relation between these abilities to segment objects, represent them as persisting and track their causal interactions and knowledge about objects? Clearly having an object-index stuck to an object is not the same thing as having knowledge about the object's location and movements. (If it were, we'd face just the problems that are fatal for the Simple View.) What then is the relation between these things?

This third point is related to an issue about the relation between infant and adult capacities, one that I raised at the start of this lecture ...

What is the relation between infants' competencies with objects and adults'? Is it that infants' competencies grow into more sophisticated adult competencies? Or is it that they remain constant throught development, and are supplemented by quite separate abilities?

infant

adult

social interaction

language

time --->

The identification of the Principles of Object Perception with object-indexes suggests that infants' abilities are constant throughout development. They do not become adult conceptual abilities; rather they remain as perceptual systems that somehow underlie later-developing abilities to acquire knowledge.

Confirmation for this view comes from considering that there are discrepancies in adults' performances which resemble the discrepancies in infants between looking and action-based measures of competence ... [This links to unit 271 on perceptual expectations ...]