Introduction

This chapter will review what is known about the development of perceptual organization and categorization of objects in preverbal infants less thanl year of age, with emphasis placed on research conducted in the author's laboratory. A number of difficult and related questions will guide the discussion. First, how does the infant begin to decompose a complex configuration of visual pattern information into elements that can be used as building blocks (i.e., units of processing) for purposes of representing objects? Second, how are the surface fragments (i.e., edge segments) of a visual scene spontaneously grouped into more complex structures (i.e., shapes) that serve as the basis for the representation of objects? Third, what visual properties of objects mediate a common categorization response? Fourth, what factors control infant visual attention during presentation of complex stimulus patterns that contain multiple visual features? Fifth, what is the contribution of previously acquired knowledge to on-line, within-task performance?

Before turning to a review of the relevant evidence, it needs to be acknowledged that there has been much recent debate over the appropriate "richness" of interpretation of the performance of infants participating in looking time studies (Aslin, 2000; Baillargeon, 1999; Haith, 1998; Smith, 1999). What kinds of skills and knowledge can be attributed to infants based on visual preference outcomes? In accord with traditional constructivist views of development, some theorists argue that infants may detect low-level stimulus variables, and gradually learn to organize them by means of maturation and experience into more complex mental structures that eventually attain the status of representations (e.g., Cohen, Chaput, & Cashon, 2002). From a more nativist perspective, other theorists propose that infants may be innately possessive of deep cognitive constraints that represent core knowledge, which in time take the form of theories that organize broad domains of experience (Carey, 2000;

Spelke, 2000). The question becomes whether one should characterize the infant as being primarily perceptual or intelligent.

The position taken in this chapter represents a third position about infants, which is to consider them both perceptual and intelligent (Kellman & Arterberry, 1998; Quinn & Bhatt, 2001; Quinn, 2002a). According to this view, in the extremes of the nativist versus empiricist debate, a point which may get lost is that basic processes when put into operation in the developing infant can begin to yield functional knowledge in a fairly short period of time. This view thus emphasizes core processes that quickly give rise to acquired knowledge which can in turn influence subsequent processing. For example, much of the experimental work reported in the present chapter was conducted with infants between 3 and 7 months of age. Infants in this age range may utilize sufficiently sensitive perceptual systems and a general learning mechanism to build up a set of representations for objects, their appearance, and their behavior. The representations may then be accessed to guide on-line performance occurring within experiments. The evidence that provides support for this position in the domains of perceptual organization and categorization will now be reviewed.

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