Simplicity and generalization: Short-cutting abstraction in children’s object categorizations

Abstract

Development in any domain is often characterized by increasingly abstract representations. Recent evidence in the domain of shape recognition provides one example; between 18 and 24 months children appear to build increasingly abstract representations of object shape [Smith, L. B. (2003). Learning to recognize objects. Psychological Science, 14, 244–250]. Abstraction is in part simplification because it requires the removal of irrelevant information. At the same time, part of generalization is ignoring irrelevant differences. The resulting prediction is this: simplification may enable generalization. Four experiments asked whether simple training instances could shortcut the process of abstraction and directly promote appropriate generalization. Toddlers were taught novel object categories with either simple or complex training exemplars. We found that children who learned with simple objects were able to generalize according to shape similarity, typically relevant for early object categories, better than those who learned with complex objects. Abstraction is the product of learning; using simplified – already abstracted instances – can short-cut that learning, leading to robust generalization.

Introduction

The adaptive application of past experience to new circumstances requires the recognition of similarities between those past experiences and the present. The similarities that are relevant to useful generalizations are often embedded within many task irrelevant similarities and differences. Thus, processes of abstraction – of finding the right similarities – are crucial to theories of generalization in a variety of cognitive domains, including vision, language, social behavior, and higher level reasoning (Harnad, 2005, Macrae et al., 1994). Abstraction and generalization are also crucial to understanding the differences between immature and mature learners and between novices and experts; mature learners generally and experts more specifically seem to know the right similarities over which to generalize past experiences. This paper reports new findings on the relation between abstraction and generalization that derive from an experimental attempt to shortcut the learners’ needs to find the right similarities for themselves. The domain is the generalization of 3-dimensional object categories by 1½ to 2-year-old children.

One way or another, all theories of categorization are about abstraction. This is explicit in theories of prototype formation which propose summary descriptions of the commonalities across instances, thereby decreasing the influence of irrelevant, within-category variance on generalization (Homa et al., 1981, Posner and Keele, 1968, Rosch, 1973, Smith and Minda, 1998). Abstraction is implicit in theories of exemplar learning which use mechanisms such as selective attention to simplify available information by deemphasizing uninformative dimensions and emphasizing diagnostic ones (Nosofsky, 1984, Palmeri and Gauthier, 2004). By many accounts, young learners are deficient in these selective processes, failing to generalize what they have learned because they attend to too much information or to the wrong information (Gentner, 1988, Hartshorn et al., 1998, Keil and Batterman, 1984, Piaget, 1969). These same deficiencies also mark adult performance in domains in which they have had little experience. Like children, adult novice generalizations overly rely on immediately perceptible and salient features while experts are able to use subtle features that have been important in past experience (Barnett and Ceci, 2002, Gentner and Markman, 1997, Gick and Holyoak, 1987, Newell and Simon, 1972).

All this suggests that proper generalization requires forming the right abstraction. Considerable experimental and theoretical work suggests that forming such minimalist abstractions is best achieved by experiencing many diverse instances (Dixon and Bangert, 2004, O’Reilly and Munakata, 2000, Reeves and Weisberg, 1994). But could not just one instance also produce robust generalization, if that instance were simple in the right way with just the right properties for abstraction? That is, one might be able to short-cut training with diverse exemplars by directly teaching the relevant abstraction and, as a consequence, get broad and appropriate transfer. This is the hypothesis for the present experiment.

We test this hypothesis in the context of young children’s learning of object names. By 2½ years of age, children are skilled at generalizing object names, so skilled that they only need experience with one exemplar to generalize the name systematically to new instances by overall shape, ignoring other properties (Gershkoff-Stowe and Smith, 2004, Golinkoff et al., 1994, Heibeck and Markman, 1987, Landau et al., 1988). This ability to “fast map” (Heibeck & Markman, 1987) names of to novel objects of the same global shape occurs around the time children begin to recognize known object categories from highly abstract versions of their 3-dimensional shapes (Smith, 2003; see also Jones and Smith, 2005, Pereira and Smith, in press). The minimalist versions used in these studies were derived from a specific theory (Biederman, 1989) about the abstract internal representations of object shape that underlie adult object recognition. These objects consisted of 2–4 geometric volumes (“geons”) in a spatial arrangement that evoked common object categories (e.g., chair, cat, hat).

While recognizing geon-like versions of cats and chairs directly result from a process of abstraction over many instances, “fast mapping” – generalizing by shape after just one instance – is not as clearly connected to abstraction. One hypothesis tying these two developmental achievements together is that these shape-sensitive children are able to abstract structural information from texture and color-rich stimuli even after one training exemplar. In order to abstract shape information, a child must deemphasize differences on other dimensions and highlight shape. However, children with very little category experience may have trouble doing this for themselves and are thus unable to fast-map or identify abstract versions of known objects. This provides the basis for testing our hypothesis: by providing the learner with the right simplification, we can simulate abstraction and thus promote generalization. To this end, our participants are young children, who do not yet systematically generalize object names by shape (Gershkoff-Stowe & Smith, 2004) and are not expected to recognize simplified abstractions of common objects (Smith, 2003). Can we bolster children’s generalizations by providing them with simplified abstractions as the training exemplars?