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The basic idea (illustrated in figure 1 below) of the visual indexing and binding mechanism is can be summarized as follows: Certain proximal events (e.g., the appearance of a new visual object) causes an index to be grabbed (since there is only a small pool of such indexes this may sometimes resulting in an existing binding being lost). As new properties of the inducing element are detected they are associated with the index that points to that object. This, in effect, provides a mechanism for connecting elements of an evolving representation with elements (i.e., objects) in the world. By virtue of this causal connection, the cognitive system can refer to any of a small number of primitive visual objects.

To have this sense of reference is to be able to access the referents in certain ways: to interrogate them in order to determine some of their properties, to evaluate multi-place predicates over them, to move focal attention to them, and in general to bind cognitive arguments to them, as would have to be done in order to execute a motor command towards them. The important thing here is that the inward arrows are purely causal and are instantiated by the non-conceptual apparatus of what's been called early vision. 

Figure 1: Sketch of the types of connections established by visual indexes between the primitive visual objects or proto-objects projecting from parts of a scene, and parts of conceptual structures, depicted here as a network. (Taken with permission from Pylyshyn's VISUAL INDEXES, PRECONCEPTUAL OBJECTS, AND SITUATED VISION, to appear in special issue of Cognition on Objects and Attention)