The research will investigate how human operators interact with automated manufacturing systems, with a view to developing models to support the rational design of the role of human operators in such systems. In particular, it will investigate the conditions which lead to human intervention in the control of automated systems. A real time interactive simulation will allow operators to experiment with different modes and strategies of intervention, and discover when to take control and when to hand it back. Particular attention will be paid to the human role under two system control policies. The first is hierarchical, where the human interacts with the system through one central controller. The second, which has not been empirically investigated in this context before, is heterarchical, where control is distributed among all the machines in the manufacturing cell and the human is just one of many entities. This research will further our understanding of human-machine symbiosis, and will lead to improvements in advanced manufacturing systems which, having a sound scientific basis, will help to make such systems more productive and competitive.