Trim Size: 7in x 10in Wixted-Vol3k c08.tex V1 - 09/30/2017 9:13 P.M. Page 275 CHAPTER 8 Categorization and Concepts ROBERT L. GOLDSTONE, ALAN KERSTEN, AND PAULO F. CARVALHO INTRODUCTION Issues related to concepts and catego- rization are nearly ubiquitous in psychology Concepts are the building blocks of thought. because of people’s natural tendency to They are critically involved when we rea- perceive a thing as something. We have a son, make inferences, and try to generalize powerful impulse to interpret our world. our previous experiences to new situations. This act of interpretation, an act of “seeing Behind every word in every language lies something as X” rather than simply seeing it a concept, although there are concepts, like (Wittgenstein, 1953), is fundamentally an act the small plastic tubes attached to the ends of categorization. of shoelaces, that we are familiar with and The attraction of research on concepts is k k can think about even if we do not know that an extremely wide variety of cognitive that they are called aglets. Concepts are acts can be understood as categorizations indispensable to human cognition because (Kurtz, 2015; Murphy, 2002). Identifying the they take the “blooming, buzzing confu- person sitting across from you at the breakfast sion” (James, 1890, p. 488) of disorganized table involves categorizing something as your sensory experiences and establish order spouse. Diagnosing the cause of someone’s through mental categories. These mental illness involves a disease categorization. categories allow us to make sense of the Interpreting a painting as a Picasso, an arti- world and predict how worldly entities will fact as Mayan, a geometry as non-Euclidean, behave. We see, hear, interpret, remember, a fugue as baroque, a conversationalist as understand, and talk about our world through charming, a wine as a Bordeaux, and a gov- our concepts, and so it is worthy of reflec- ernment as socialist are categorizations at tion time to establish where concepts come various levels of abstraction. The typically from, how they work, and how they can unspoken assumption of research on concepts best be learned and deployed to suit our is that these cognitive acts have something cognitive needs. in common. That is, there are principles that explain many or all acts of categorization. AQ1 We are grateful to Brian Rogosky, Robert Nosofsky, John This assumption is controversial (see Medin, Kruschke, Linda Smith, and David Landy for helpful Lynch, & Solomon, 2000), but is perhaps comments on earlier drafts of this chapter. This research justified by the potential payoff of discover- was funded by National Science Foundation REESE grant DRL-0910218, and Department of Education IES ing common principles governing concepts grant R305A1100060. in their diverse manifestations. 275 k Trim Size: 7in x 10in Wixted-Vol3k c08.tex V1 - 09/30/2017 9:13 P.M. Page 276 276 Categorization and Concepts The desirability of a general account of each other, and assigning values of 0 and 1 to concept learning has led the field to focus a dimension is arbitrary. For example, for a its energy on what might be called generic color dimension, red may be assigned a value concepts. Experiments typically involve arti- of 0 and blue a value 1. The exact category ficial categories that are hopefully unfamiliar structure of Table 8.1 has been used in at least to the subject. Formal models of concept 30 studies (reviewed by J. D. Smith & Minda, learning and use are constructed to be able to 2000) and instantiated by stimuli as diverse handle any kind of concept irrespective of its as geometric forms, yearbook photographs, content. Although there are exceptions to this cartoons of faces (Medin & Schaffer, 1978), general trend (Malt, 1994; Ross & Murphy, and line drawings of rocket ships. These 1999), much of the mainstream empirical researchers are not particularly interested and theoretical work on concept learning is in the category structure of Table 8.1 and concerned not with explaining how particular are certainly not interested in the catego- concepts are created, but with how concepts rization of rocket ships per se. Instead, they in general are represented and processed. choose their structures and stimuli so as to be One manifestation of this approach is that (a) unfamiliar (so that learning is required), the members of a concept are often given (b) well controlled (dimensions are approx- an abstract symbolic representation. For imately equally salient and independent), example, Table 8.1 shows a typical notation (c) diagnostic with respect to theories of used to describe the stimuli seen by a subject category learning, and (d) potentially gen- in a psychological experiment or presented eralizable to natural categories that people to a formal model of concept learning. Nine learn. Work on generic concepts is valuable k objects belong to two categories, and each if it turns out that there are domain-general k object is defined by its value along four principles underlying human concepts that binary dimensions. In this notation, objects can be discovered. Still, there is no a pri- from Category A typically have values of 1 ori reason to assume that all concepts will on each of the four dimensions and objects follow the same principles, or that we can from Category B usually have values of 0. generalize from generic concepts to naturally The dimensions are typically unrelated to occurring concepts. Table 8.1 A Common Category Structure WHAT ARE CONCEPTS? Dimension Concepts, Categories, and Internal Category Stimulus D1 D2 D3 D4 Representations A11110 A21010A good starting place is Edward Smith’s Category A A31011(1989) characterization that a concept is “a A41101mental representation of a class or individual A50111and deals with what is being represented and B11100how that information is typically used during Category B B20110 B30001the categorization” (p. 502). It is common to B40000distinguish between a concept and a category. A concept refers to a mentally possessed idea Source: From Medin and Schaffer (1978). Copy- right 1978 by the American Psychological Association. or notion, whereas a category refers to a Reprinted with permission. set of entities that are grouped together. k Trim Size: 7in x 10in Wixted-Vol3k c08.tex V1 - 09/30/2017 9:13 P.M. Page 277 What Are Concepts? 277 The concept dog is whatever psychological particular objects belong, and how well, to state signifies thoughts of dogs. The category the concept’s extension. dog consists of all the entities in the real world that are appropriately categorized as Equivalence Classes dogs. The question of whether concepts determine categories or vice versa is an Another important aspect of concepts is that important foundational controversy. On the they are equivalence classes. In the classical one hand, if one assumes the primacy of notion of an equivalence class, distinguish- external categories of entities, then one will able stimuli come to be treated as the same tend to view concept learning as the enter- thing once they have been placed in the prise of inductively creating mental structures same category (Sidman, 1994). This kind of that predict these categories. One extreme equivalence is too strong when it comes to version of this view is the exemplar model human concepts because even when we place of concept learning (Estes, 1994; Medin & two objects into the same category, we do not Schaffer, 1978; Nosofsky, 1984), in which treat them as the same thing for all purposes. one’s internal representation of a concept is Some researchers have stressed the intrinsic nothing more than the set of all of the exter- variability of human concepts—variability nally supplied examples of the concept to that makes it unlikely that a concept has the which one has been exposed. If, on the other same sense or meaning each time it is used hand, one assumes the primacy of internal (Barsalou, 1987; Connell & Lynott, 2014; mental concepts, then one tends to view exter- Thelen & Smith, 1994). Still, the extent to nal categories as the end product of using which perceptually dissimilar things can k these internal concepts to organize observed be treated equivalently given the appropri- k entities. Some practitioners of a “concepts ate conceptualization is impressive. To the first” approach argue that the external world biologist armed with a strong “mammal” does not inherently consist of rocks, dogs, concept, even whales and dogs may be and tables; these are mental concepts that treated as commensurate in many situations organize an otherwise unstructured exter- related to biochemistry, child rearing, and nal world (Lakoff, 1987). Recent research thermoregulation. indicates that concepts’ extensions (the class Equivalence classes are relatively imper- of items to which the concept applies) and vious to superficial similarities. Once one intensions (the features that distinguish that has formed a concept that treats all skunks class of items) do not always cohere with as equivalent for some purposes, irrelevant each other (Hampton & Passanisi, 2016). variations among skunks can be greatly For example, dolphins and whales are often de-emphasized. When people are told a story judged to have many of the features charac- in which scientists discover that an animal teristic of an internal representation of fish that looks exactly like a raccoon actually con- (e.g., swims, lives in oceans, and has fins), tains the internal organs of a skunk and has but are still placed in the extensional set of skunk parents and skunk children, they often mammals rather than fish. The implication categorize the animal as a skunk (Keil, 1989; is that a complete model of concepts may Rips, 1989). When people classify objects require at least partially separate represen- into familiar, labeled categories such as chair, tations for intensions and extensions, rather then their memory for the individuating infor- than a more parsimonious model in which mation about the objects is markedly worse a concept’s intension determines whether (Lupyan, 2008a).