The Development of Categorization

Article excerpt

Categorization is indubitably an important cognitive process for humans (as well as other animals, Murai, Kosugi, Tomonaga, Tanaka, Matsuzawa, & Itakura, 2005), one that we constantly engage in to adapt to a very rich environment. We have a powerful impulse to interpret our world. This act of interpretation is fundamentally an act of categorization. We can go back in history at least to Aristotle (see his work on Categories, 350 B.C.E.) and along this way we find discussions of categories often appearing in philosophers' books. The issue of categorization is also an historically early topic in psychology (see Hull's experiment in 1920), and a considerable amount of research has been continuously dedicated to it up until the present. One could ask then: Why a special issue on categorization at this point in time?

Although the general topic of categorization is venerable, relatively recently we cognitive scientists have changed our view about categorization. We have moved from considering taxonomies (or categories based in logic) as the "real," mature kind of categorization to understanding that there are multiple kinds of similarities that are taken into account when one groups items (Barsalou, 1993, 2003; Medin, Goldstone, & Gentner, 1993; Ross & Murphy, 1999). More than this, we know now that children, like adults, are able to take into account multiple types of similarity in categorization (e.g., Deak & Bauer, 1995; Waxman & Namy, 1997). We do not know, though, the precise course along which this ability develops: what triggers it; whether internal mechanisms or external cues are more powerful in shaping it; how concepts are "born" in our heads; or how do we end up, as adults, to flexibly shift between several possible interpretations for one stimulus in accordance with contextual demands. This is why we have endeavored to gather some of the leading researchers who struggle to solve these problems, and to put together a special issue on the development of categorization.

A timely topic in research on the development of categorization is the debate over perceptual versus conceptual influences on categorization. Are our categories based on perceptual features that cumulatively ground concepts? Or, are our categories based on some underlying conceptual knowledge? Some authors consider that it is mainly through perceptual learning that we end up with abstract concepts, and that we need to look at categorization as a dynamic process that takes place in the physical world (Goldstone, 2004; Smith, 2005). Others argue that our categories have at their core some kind of hidden, essential knowledge which goes beyond the perceptual information that is extracted from the interaction with stimuli (Gelman, 2003). The first group of articles in this issue offer answers to this question. Many of the articles argue that the influence of perceptual and attentional processes on conceptual development has been underemphasized. For example, Fisher argues for the importance of considering attentional and perceptional factors in conceptual development. Her argument is that views in which children's categories are constructed on the basis of their theories place implausibly high demands on children's very limited executive control of attention. Similarly, Namy, Gentner, and Clepper underline the role that comparing perceptually similar items has for observing the conceptual relations they have, and develop systematic experiments to show how much perceptual similarity is needed for this. Oakes and Kovack-Lesh describe the role that memory and perceptual processes (such as presenting items in pairs or singly) play in infants' categorization. Also, Quinn, Lee, Pascalis, and Slater use inverted human stimuli to show that infants' pattern of categorization is well explained in terms of perceptual expertise rather than humans being an a priori specialized domain. All of these articles bring evidence that perception is an important process that influences categorization, which may ultimately lead to conceptual knowledge. …