Indexing and the object concept: developing `what' and `where' systems

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Abstract

The study of object cognition over the past 25 years has proceeded in two largely non-interacting camps. One camp has studied object-based visual attention in adults, while the other has studied the object concept in infants. We briefly review both sets of literature and distill from the adult research a theoretical model that we apply to findings from the infant studies. The key notion in our model of object representation is the `sticky' index, a mechanism of selective attention that points at a physical object in a location. An object index does not represent any of the properties of the entity at which it points. However, once an index is pointing to an object, the properties of that object can be examined and featural information can be associated with, or `bound' to, its index. The distinction between indexing and feature binding underwrites the distinction between object individuation and object identification, a distinction that turns out to be crucial in both the adult attention and the infant object-concept literature. By developing the indexing model, we draw together two disparate sets of literature and suggest new ways to study object-based attention in infancy.

Section snippets

Objects and indexes

Although making best use of our limited processing resources demands selective attention9, 10, it is likely that attention can span more than a single object at a time. Without this, it would be hard to compare, or grasp a relation between, two or more objects. Our cognitive design may allow a compromise in which a small set of objects can be simultaneously attended to. In fact, we will suggest that our object indexing mechanism is limited to four indexes.

Indexing forms the basis for the

Object indexing

The central idea in our framework is the notion of an `object index'. We hypothesize a number of properties.

First, an object index is a mental token that functions as a pointer to an object.

Second, an index does not inherently represent any of the properties or features of the object pointed at. A finger can point at an object but the finger itself does not say whether the object is red or green, what shape it has, or what kind of object it is. Likewise, an object index is an entirely abstract

A model of infant object indexing

We align hitherto separate theoretical frameworks by distilling key ideas from adult object-based attention into a model of the infant object concept. Our model's basic claim (Fig. 2) is that the individuation of a physical object entails the assignment of a mental index that points at the object. Assignment is primarily determined on spatiotemporal grounds (`individuation by location'). Featural and, more generally, property information influences the indexing process in two distinct ways:

Key findings on infants' object cognition

We now discuss some recent studies of infants from the point of view of indexing theory. All the studies used measures of infant looking-times to expected and unexpected outcomes.

A seminal study by Spelke4, 37found that young infants' individuation judgments were influenced by spatiotemporal continuity (Fig. 3). We can interpret these findings as indexing by location. Take Spelke's first condition: as the first object appears, it is assigned an index. The index sticks to the object as it moves

Conclusions

We have constructed a set of theoretical notions, each of which is independently grounded in adult visual attention, and have fashioned a model of the infant `object concept'. Although we make specific proposals, our intention is not to take up a cast-iron stance on details. It is much too early for that. Instead, we have outlined a theoretical framework that can cast existing data in a new light and suggest new approaches to old questions. The classical idea of object representations as

Acknowledgements

We are particularly grateful to Susan Carey for stimulating our interest in these questions over the years, to Zenon Pylyshyn for helpful comments on an earlier draft, and to these and other members of the Princeton–Rutgers–NYU Object Group; especially Bela Julesz, Anne Treisman, Eileen Kowler, Thomas Papathomas, and Jacob Feldman for helpful discussions. This work was supported by NSF project grant SBR-9616342 awarded to A.M.L.

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