Keywords: User model, Perceptual Control Theory (PCT)

Conventional behavioral models can be broadly classed as stimulus-driven (bottom-up, S?R) and brain-driven (top-down, cognitive). Perceptual control theory (PCT) uses a model that has features of both classes, and so can be difficult to distinguish from either one. The difference in PCT is not just in the model of the organism, but in the assumed properties of the world in which the organism behaves. We discuss and experimentally demonstrate the basic models, and the worlds in which they can operate properly. The results show, we believe, that PCT employs the only kind of model that can work in a realistic model of the world. Copyright 1999 Academic Press