Learning of role-governed and thematic categories.

Natural categories are often based on intrinsic characteristics, such as shared features, but they can also be based on extrinsic relationships to items outside the categories. Examples of relational categories include items that share a thematic relation or items that share a common role. Five experiments used an artificial category learning paradigm to investigate whether people can learn role-governed and thematic categories without explicit instruction or linguistic support.

Concept formation and categorization of complex, asymmetric, and impossible figures.

Impossible figures are striking examples of inconsistencies between global and local perceptual structures, in which the overall spatial configuration of the depicted image does not yield a coherent three-dimensional object. In order to investigate whether structural "impossibility" is an important perceptual property of depicted objects, we used a category formation task in which subjects were asked to divide pictures of shapes into groups that seemed most natural to them. Category formation is usually unidimensional, such that sorting is dominated by a single perceptual property, so this task can serve as a measure of which dimensions are most salient.