Training to break the barriers of habit in reasoning about unusual faults.

Two studies of experienced operators in a process-control plant aimed to improve diagnosis of unusual multiple faults through training. A process-tracing methodology analyzed operators' concurrent verbalizations and actions during simulated fault scenarios. In Study 1, training increased awareness of multiple faults and provided a heuristic for switching to a representation that included multiple-fault hypotheses. Training had no effect on diagnostic accuracy, although fewer incorrect single-fault hypotheses were regenerated. In Study 2, operators practiced identifying the inconsistencies between a single-fault hypothesis and fault symptoms and modifying this hypothesis into a consistent multiple-fault hypothesis. Training improved diagnostic accuracy because of improved hypothesis modification processes.