A new investigation of the nature of abstract categories

A New Investigation of the Nature of Abstract Categories Loes Stukken (Loes.Stukken@student.kuleuven.be) Steven Verheyen (Steven.Verheyen@psy.kuleuven.be) Matthew J. Dry (Matt.Dry@psy.kuleuven.be) Gert Storms (Gert.Storms@psy.kuleuven.be) University of Leuven, Department of Psychology Tiensestraat 102, B-3000, Leuven Belgium Abstract Concrete and abstract categories are alike in that they show graded structure. They are also said to differ in that the degree of feature overlap between a category and its exemplars can predict the graded structure of the former, but not of the latter kind of category. We show how one can improve upon this prediction by taking distinctive features into consideration and argue that concrete and abstract categories might not be that differently structured after all. Keywords: abstract categories; graded structure; typicality; characteristic features; polymorphous concept; familiarity. Introduction Well-defined categories (e.g., odd numbers, plane geometry figures, Armstrong, Gleitman, & Gleitman, 1983), ad hoc categories (e.g., ways to make friends, things that could fall on your head, Barsalou, 1983), abstract categories (e.g., beliefs, crimes, Hampton, 1981), and well-established, concrete categories (e.g., fruit, vehicles, Rosch, 1973) are alike in that they all present with graded structure. That is, some of their exemplars are consistently judged to be more typical of or representative for the category than others. Graded category structure also becomes apparent in category verification where the more typical an exemplar is, the faster it will be judged a true category member. Rosch (1973) was among the first to demonstrate this relationship in concrete categories. Armstrong et al. (1983) and Hough and Pierce (1989) showed it also holds in well-defined and ad hoc categories, respectively. In addition, typical exemplars are generally among the first to be generated in response to the category label and across participants they are generated more often than less typical category members (for early demonstrations in concrete and ad hoc categories see Mervis, Catlin, & Rosch, 1976 and Barsalou, 1985, respectively). Other processing advantages of typical over atypical category members have been shown in concrete categories, but attempts to demonstrate similar effects in well-defined or ad hoc categories have generally not been undertaken. Studies pertaining to the internal structure of abstract categories are even rarer. The presence of graded structure in a varied range of categories need not necessarily indicate that these are all represented in the same manner. The most generally accepted account of graded structure to have arisen from the study of concrete categories is probably the one in which category members are represented by characteristic features. The more of these features an exemplar shares with the category as a whole, the more typical the exemplar is of the category (Hampton, 1979; Rosch & Mervis, 1975). As penguins do not have the features and in common with most other birds, they are considered to be among the atypical category members. The internal structure of many ad hoc and well-defined categories does not adhere to this shared feature account, however. Barsalou (1985) illustrates how participants’ estimates of the number of times they had previously encountered an item as a category member and the item’s ability to fulfill the goal served by its ad hoc category, provide a better account of the item’s judged typicality. Those food items that are often thought of as diet products and those that are ideally suited for minimizing one’s intake of calories, Barsalou found to be the worst examples of the ad hoc category foods not to eat on a diet for instance. Larochelle, Richard, and Soulieres (2000) ascribe well- defined categories’ apparent graded structure in category verification to the exemplars’ familiarity and category dominance. When the influences of these variables are controlled for, reliable categorization time differences no longer come about. With categories considered the building blocks of cognition (Pinker, 1997) the question of which categories constitute truly distinct kinds (and which ones do not) becomes one of central importance in cognitive science. In what follows, we will review evidence that pertains to the possibly different nature of concrete and abstract categories. As we already indicated, studies addressing the internal structure of abstract categories are scarce, but nevertheless seem to suggest its origin differs from that of concrete categories. Especially a study by Hampton (1981) favours this conclusion. Hampton found that the polymorphous concept - a measure of the number of characteristic features shared by category and exemplar, originating from the concrete categories literature - did not prove adequate in predicting the graded structure of a number of abstract categories. We will show how one can improve upon this prediction by taking distinctive features into consideration and argue that concrete and abstract categories might not be that differently structured after all.