The role of functional form in causal-based categorization

Two experiments tested how the functional form of the causal relations that link features of categories affects category-based inferences. Whereas independent causes can each bring about an effect by themselves, conjunctive causes all need to be present for an effect to occur. The causal model view of category representations is extended to include a representation of conjunctive causes and then predictions are derived for 3 category-based judgments: classification, conditional feature predictions, and feature likelihoods. Experiment 1 revealed that subjects' judgments on all 3 tasks were not only sensitive to whether causes were independent or conjunctive but also conformed to the causal model predictions, albeit with an important exception. Experiment 2 revealed that inferences with independent and conjunctive causes were affected quite differently by a manipulation of the strengths of the causal relations (and in the manner predicted by the model). This is the 1st study to show how a single representation of a category's causal knowledge can account for 3 category-based judgments with the same model parameters. Other models of causal-based categories are unable to account for the observed effects.