Emergence of Hierarchical Versus Similarity Relations in Known Categories

The structure of organized categories is argued to be hierarchical and is suggestive of the taxonomy of the “superordinate-basic-subordinate” categorization schema (Rosch, 1978). In contrast, the similarity of a member to its category may also be indicative of the extent of transitivity that exists within a category. To investigate the role that hierarchical and similarity relations contribute to categorization [adapted from Sloman (1998)], we asked 49 participants to evaluate the probability of a conclusion statement based on the given fact. In condition 1, participants were only provided a fact and conclusion, while in condition 2 participants were also provided with a hierarchical relation (e.g., All pines are wood; Fact: All 'wood' is fibrous; Conclusion: All 'pine' is fibrous). Condition 1 can be solved using hierarchical relations, while condition 2, an inductive reasoning task, can be solved with similarity or hierarchical relations. We used 20 natural and 20 artificial categories validated by Gruenenfelder (1984), with typical and atypical examples in each category. A factorial ANOVA revealed a main effect of condition, F(1,48) = 69.53, p < 0.001, indicating that providing hierarchical relations increased overall agreement between fact and conclusion. We also found the expected main effect of typicality, F(1,48) = 45.39, p < 0.001. An interaction between condition and typicality was also detected, F(1,48) = 4.79, p = 0.034, however, a metric multidimensional scaling of average ratings per category for conditions 1 and 2 showed that agreement between the fact and conclusion might rely on the type of category rather than typicality.