Expertise and category-based induction.

The authors examined inductive reasoning among experts in a domain. Three types of tree experts (landscapers, taxonomists, and parks maintenance personnel) completed 3 reasoning tasks. In Experiment 1, participants inferred which of 2 novel diseases would affect "more other kinds of trees" and provided justifications for their choices. In Experiment 2, the authors used modified instructions and asked which disease would be more likely to affect "all trees." In Experiment 3, the conclusion category was eliminated altogether, and participants were asked to generate a list of other affected trees. Among these populations, typicality and diversity effects were weak to nonexistent. Instead, experts' reasoning was influenced by "local" coverage (extension of the property to members of the same folk family) and causal-ecological factors. The authors concluded that domain knowledge leads to the use of a variety of reasoning strategies not captured by current models of category-based induction.

On the importance of comparative research: the case of folkbiology.

If our goal as researchers is to understand the range and complexity of human conceptual development, increased attention to comparative research is essential. I draw on research in the domain of folkbiology-commonsense understandings of plants and animals--to argue that several lines of comparative research are needed to understand the acquisition of folkbiology in particular and conceptual development in general. First, comparisons are needed between children and adults within a given society. It is impossible to understand the process of conceptual development without a detailed look at adult endstates in a domain. Second, comparisons are needed between adult endstates in different contexts. For a complete understanding of conceptual development we must understand the range of variability of adult conceptual systems. Finally, comparisons are needed among children developing in different contexts. Such research complements comparative work on adults and would serve to distinguish between universal and particular patterns of development and thus to inform and constrain accounts of conceptual development.

Tall is typical: central tendency, ideal dimensions, and graded category structure among tree experts and novices.

Many accounts of categorization equate goodness-of-example with central tendency for common taxonomic categories; the best examples of a category are average members--those that are most similar to most other category members. In the present study, we asked 24 tree experts and 20 novices to rate goodness-of-example for a sample of 48 trees and found (1) that the internal structure of the category tree differed between novices and experts and (2) that central tendency did not determine goodness-of-example ratings for either group. For novices, familiarity determined goodness-of-example ratings. For experts, the "ideal" dimensions of height and weediness, rather than average similarity to other trees, were the primary predictors of goodness-of-example ratings for experts. The best examples of tree were not species of average height, but of extreme height. The worst examples were the weediest trees. We also found systematic differences in predictors of goodness-of-example as a function of type of expertise. We argue that the internal structure of taxonomic categories can be shaped by goal-related experience and is not necessarily a reflection of the attributional structure of the environment. Implications for models of category structure and category learning are discussed.

Beyond labeling: the role of maternal input in the acquisition of richly structured categories.

Recent research shows that preschool children are skilled classifiers, using categories both to organize information efficiently and to extend knowledge beyond what is already known. Moreover, by 2 1/2 years of age, children are sensitive to nonobvious properties of categories and assume that category members share underlying similarities. Why do children expect categories to have this rich structure, and how do children appropriately limit this expectation to certain domains (i.e., animals vs. artifacts)? The present studies explore the role of maternal input, providing one of the first detailed looks at how mothers convey information about category structure during naturalistic interactions. Forty-six mothers and their 20- or 35-month-old children read picture books together. Sessions were videotaped, and the resulting transcripts were coded for explicit and implicit discussion of animal and artifact categories. Sequences of gestures toward pictures were also examined in order to reveal the focus of attention and implicit links. drawn between items. Results indicate that mothers provided a rich array of information beyond simple labeling routines. Taxonomic categories were stressed in subtle and indirect ways, in both speech and gesture, especially for animals. Statements and gestures that linked two pictures were more frequent for taxonomically related animal pictures than for other picture pairs. Mothers also generalized category information using generic noun phrases, again more for animals than for artifacts. However, mothers provided little explicit discussion of nonobvious similarities, underlying properties, or inductive potential among category members. These data suggest possible mechanisms by which a notion of kind is conveyed in the absence of detailed information about category essences.

Categorization and reasoning among tree experts: do all roads lead to Rome?

To what degree do conceptual systems reflect universal patterns of featural covariation in the world (similarity) or universal organizing principles of mind, and to what degree do they reflect specific goals, theories, and beliefs of the categorizer? This question was addressed in experiments concerned with categorization and reasoning among different types of tree experts (e.g., taxonomists, landscape workers, parks maintenance personnel). The results show an intriguing pattern of similarities and differences. Differences in sorting between taxonomists and maintenance workers reflect differences in weighting of morphological features. Landscape workers, in contrast, sort trees into goal-derived categories based on utilitarian concerns. These sorting patterns carry over into category-based reasoning for the taxonomists and maintenance personnel but not the landscape workers. These generalizations interact with taxonomic rank and suggest that the genus (or folk generic) level is relatively and in some cases absolutely privileged. Implications of these findings for theories of categorization are discussed.

Emerging differentiation of folkbiology and folkpsychology: attributions of biological and psychological properties to living things.

Research suggests that for adults, "folkpsychology" and "folkbiology" represent distinct conceptual domains for reasoning about living things. However, it is not clear whether these domains are distinct for children; past work suggests that the 2 systems are confused until age 10, and that radical theory change accounts for eventual differentiation. To examine this claim, 16 subjects each at ages 6, 8, and adult were shown pictures of predatory and domestic animals and asked whether each animal displayed a variety of biological properties (e.g., has blood) and psychological properties (e.g., can think, can feel angry). Subjects at all ages showed clearly different attribution patterns for biological versus psychological properties. This dissociation of attribution patterns provides evidence that by kindergarten, notions of folkpsychology and folkbiology are sufficiently differentiated to constitute distinct and independent conceptual domains. This in turn suggests that radical theory change regarding living things either occurs prior to the beginning of formal education, or does not explain the development of folkbiological knowledge.

The effects of object orientation and object type on children's interpretation of the word big.

Previous research indicates that preschool children have persistent difficulty interpreting big: 4-5-year-olds typically interpret big to mean tall, and 3-year-olds fail to use any consistent interpretation. We propose that children's interpretation may vary depending on 2 contextual factors: type of object and orientation of object. 40 children (ages 3 and 5) each saw 35 pairs of items and, for each pair, were asked to point to "the big one." Type of object was varied by showing each child 3 kinds of objects: "people," "brownies," and rectangles. Orientation of object was varied by presenting objects either standing perpendicular to the tabletop (vertical condition) or lying flat on the tabletop (horizontal condition). Older children relied on height more consistently than younger children, all subjects relied on area more often in the horizontal condition than in the vertical condition, and 3-year-olds relied on height more when judging the bigness of people than of rectangles matched for size. Taken together, these results demonstrate that contextual factors clearly influence children's responses. These results demonstrate the interplay of cognitive and semantic factors in the process of semantic development.