Caricatures and Prototypes 1 Conceptual Interrelatedness and Caricatures Isolated and Interrelated Concepts

Concepts are interrelated to the extent that the characterization of one concept is influenced by another concept, and isolated to the extent that the characterization of one concept is independent of other concepts. The relative categorization accuracy of the prototype and caricature of a concept can be used as a measure of concept interrelatedness. The prototype is the central tendency of a concept, whereas a caricature deviates from the concept’s central tendency in the direction opposite to the central tendency of other acquired concepts. The prototype is predicted to be relatively well categorized when a concept is relatively independent of other concepts, but the caricature is predicted to be relatively well categorized when a concept is highly related to other concepts. Support for these predictions comes from manipulations of the labels given to simultaneously acquired concepts (Experiment 1) and the order of categories during learning (Experiment 2). Caricatures and Prototypes 3 Conceptual Interrelatedness and Caricatures Concepts seem to be simultaneously connected to each other and to the external world. On the one hand, concepts seem to gain their meaning by the role that they play within a network of concepts (Collins & Quillian, 1969; Field, 1977). The notion of a “conceptual web” by which concepts all mutually define one another has been highly influential in all of the major fields that comprise cognitive science, including linguistics (Saussure, 1915/1959), computer science (Lenat & Feigenbaum, 1991), psychology (Landauer & Dumais, 1997), and philosophy (Block, 1999). However, there is also dissatisfaction in some quarters with the circularity of this conceptual web account. Researchers have argued that concepts must be grounded in the external world rather than merely related to each other (Harnad, 1990). The British empiricists argued that our conceptual ideas originate in recombinations of sensory impressions (Hume, 1740/1973). More recently, Barsalou (1999; Goldstone & Barsalou, 1998; Solomon & Barsalou, 2001) has argued that concepts are not amodal, completely abstracted symbols, but rather are intrinsically perceptually based. In an attempt to reconcile arguments for a conceptual web and externally grounded concepts, Goldstone (1996) described a continuum between purely isolated and purely interrelated concepts, arguing that a concept is interrelated to the extent that its characterization is influenced by other concepts. Goldstone’s empirical basis for the continuum was the convergence of a set of experimental manipulations and measures of conceptual interrelatedness. A set of manipulations was designed to influence the degree of interrelatedness between simultaneously acquired concepts, and the influence of these manipulations was gauged by a set of measures of interrelatedness. These experiments gave support to the hypothesis that fairly minimal experimental manipulations were capable of changing how influential one concept was on another concept’s representation and processing. The goal of the current experiments is to further test the claim for a continuum between isolated and interrelated concepts, using rich and naturalistic stimuli, and new manipulations and measures of interrelatedness. Caricatures and Prototypes 4 Isolated and Interrelated Concepts In evaluating the claim for a continuum between isolated and interrelated concepts, it is helpful to consider theories at the two poles of the continuum. We will consider representative models of isolated and interrelated concepts, leaving a fuller description to Goldstone (1996). Conceptual interrelatedness is a component of many linguistic treatments of concepts. Ferdinand de Saussure (1915/1959) argued that all concepts are completely “negatively defined,” that is, defined solely in terms of other concepts. He contended that “language is a system of interdependent terms in which the value of each term results solely from the simultaneous presence of the others” (p. 114) and that “concepts are purely differential and defined not in terms of their positive content but negatively by their relations with other terms in the system” (p. 117). This notion has evolved into the modern treatment of semantic networks (Collins & Quillian, 1969; Quillian, 1967). In these networks, concepts are represented by nodes in a network, and gain their functionality by their links to other concept nodes. Often times, these links are labeled, in which case different links refer to different kinds of relations between nodes. Dog would be connected to Animal by an Is-a link, to Bone by an Eats link, and to Paw by a Has-a link. Lenat and Feigenbaum have argued (1991) that interconceptual linkages are sufficient for establishing conceptual meanings even without any external grounding of the concepts. A computational approach to word meaning that has received considerable recent attention has been to base word meanings solely on the patterns of co-occurrence between a large number of words in an extremely large text corpus (Burgess, Livesay, & Lund, 1998; Burgess & Lund, 2000; Landauer & Dumais, 1997). Mathematical techniques are used to create vector encodings of words that efficiently capture their co-occurrences. If two words, such as “cocoon” and “butterfly” frequently co-occur in an encyclopedia or enter into similar patterns of cooccurrence with other words, then their vector representations will be highly similar. The meaning of a word, its vector in a high dimensional space, is completely based on the contextual similarity of the word to other words. Finally, researchers have argued that concepts are frequently characterized by their associative relations to other concepts. Barr and Caplan (1987) provide evidence, by having subjects list features associated with words, that many concepts are characterized by what they call “extrinsic features,” features that are “represented as the relationship between two or more entities” (p. 398). Caricatures and Prototypes 5 From the theories above, one might conclude that concepts cannot stand alone, and there could not be such a thing as a system with only one concept (Stich, 1983). However, if one looks at the field of pattern recognition rather than theories inspired by linguistics, then examples of isolated concepts become apparent. One way to conceive of an isolated concept is as a feature detector. A feature detector can become active when an input with a particular perceptual feature is present. Ascending in complexity, a concept can also be represented as a template in a physical or more abstract space (Edelman, 1999). If patterns are categorized by comparing them with stored templates for categories, the representation of the categories do not depend on the other categories. A category’s representation is simply the image that best matches the members of the category. It is possible to have a feature detector or template for a concept without having any other concepts in the system. Categorizing an object may require comparing the relative degrees of match of the object to the representations for the candidate categories (Nosofsky, 1986), but if the categories themselves are represented by templates or feature detectors, then each can exist independently of the other categories. A comparison of these representative examples of interrelated and isolated concepts suggests a useful heuristic for assessing degree of interrelatedness. A Concept X is dependent on Concept Y to the extent that Concept X cannot exist without Concept Y. If the concept Vermicelli is represented as “thinner pasta than spaghetti” then no system could possess Vermicelli without also possessing Spaghetti. However, if the concept Vermicelli is represented by “a long pasta with a typical diameter of 6 mm” then possession of the concept does not depend upon possession of Spaghetti. Partial degrees of dependency owe to the multi-faceted nature of conceptual representations. A person’s concept of Vermicelli may incorporate both characterizations given above, and the relative importance of these characterizations determines how much Vermicelli’s representation is affected by the presence or absence of a Spaghetti concept. Prototypes and Caricatures Consider the example of two categories shown in Figure 1. Categories A and B each have 6 members, and each member has a unique combination of values on Dimensions 1 and 2. We will define the prototype of a category as the central tendency of the category along each of dimensions (Posner & Keele, 1968; Reed, 1972). The prototype of Category A has a Dimension 1 value of 2, while Category B’s Caricatures and Prototypes 6 prototype has a value of 4. In the experiments that follow, we use uniform distributions of dimension values in constructing categories, and consequently our description of a category prototype remains the same if we define central tendency as the average or median. -----------------------------INSERT FIGURE 1 ABOUT HERE ------------------------------We will define a caricature of a category as an object that assumes dimension values that depart from the central tendency of the category in the opposite direction of the central tendency of other simultaneously acquired concepts. In Figure 1, “X” represents the prototype of Category B, and “Y” represents a caricature of Category B. Y has a value of 5 on Dimension 1, and this value is a distortion of Category B’s central tendency in the direction opposite of Category A. This definition of caricature captures the intuitive notion of a caricature as an exaggeration. If Category B has a large value on Dimension 1 (relative to Category A), then the caricature of Category B exaggerates this large value, in the same way that a newspaper caricature exaggerates distinctive facial features of a politician. The current experiments investigate the conditions under which the prototype or caricature of a category is more easily categorized. On the