Several authors have distinguished automatic behaviour of routine or well-learnt action sequences from controlled behaviour of novel actions. Tn this paper we present an interactive activation model of routine action selection based on the Contention Scheduling theory of Norman & Shallice (1986). The model, developed in the specific domain of coffee preparation, provides a good account of normal behaviour in a complex yet routine task. In addition, we report lesioning studies which show breakdown of action selection qualitatively similar to that seen in a variety of neurological patients (action disorganisation syndrome, utilisation behaviour, and Parkinson's disease). These lesioning studies are based on the systematic variation of critical system parameters. Such parameters, which are implicit in all interactive activation models, raise complex methodological issues relating to the criticality of their values. We address these issues by reporting results of a detailed exploration of the parameter space.
