Categorization is one of the most fascinating aspects of human cognition. It refers to the process of organizing sensory experience into groups. This is an ability we share to some extent with other animals (e.g. Herrnstein & Loveland, 1964), and is key to our understanding of the world. Humans seem particularly adept at the systematic and productive combination of elementary concepts to develop complex thought. All in all, it is hard to envisage much of cognition without concepts.
The study of categorization has a long history (e.g. Hull, 1920). It is usually considered a particular research theme of cognitive psychology, cognitive science, and cognitive neuroscience. Categorization relates intimately to many other cognitive processes, such as learning, language acquisition and production, decision making, and inductive reasoning. What all these processes have in common is that they are inductive. That is, the cognitive system is asked to process some experience and subsequently extrapolate to novel experience.
A formal model of categorization is taken to correspond to any description of categorization processes in a principled, lawful way. Formal models of categorization are theories that allow quantitative predictions regarding the categorization behaviour of participants. Some formal models also make predictions about the underlying neuroscience.
Selecting the models to be discussed in this volume was difficult. Our goal was to create an accessible volume with a reasonably small number of models. As a result, there are many excellent models which we were not able to include.