In P.A. Hancock and P.A. Desmond (Eds.). Stress Workload and Fatigue. Hillsdale, NJ: Lawrence Erlbaum Associates. How Unexpected Events Produce An Escalation Of Cognitive And Coordinative Demands David D. Woods Emily S. Patterson Institute for Ergonomics The Ohio State University In Stress Workload and Fatigue. P. A. Hancock and P. Desmond (eds.) Lawrence Erlbaum, Hillsdale NJ, 2000. Explaining the Clumsy Use of Technology Each round of technological development promises to aid the people engaged in various fields of practice. After these promises result in the development of prototypes and fielded systems, those researchers who examine the reverberations of technology change have observed a mixed bag of effects, most quite different from the expectations of the technology advocates. Often the message practitioners send with their performance, their errors, and their adaptations is one of technology-induced complexity. In these cases, technological possibilities are used clumsily so that systems intended to serve the user turn out to add new burdens that congregate at the busiest times or during the most critical phases of the task (e.g., Woods, Johannesen, Cook, & Sarter, 1994, chapter 5, Woods & Watts, 1997). Although this pattern has been well documented in a variety of areas such as cockpit automation (Sarter, Woods & Billings, 1997) and many principles for more effective human-machine and human-human cooperation have been developed (e.g., Norman, 1988), we have a gaping explanatory problem. There is a striking contrast between the persistence of the optimism of developers who before the fact expect each technological development to produce significant performance improvements and the new operational complexities that are observed after the fact. It seems difficult for all kinds of people in design teams to predict or anticipate operational complexities. Yet operational complexities are easy to see when the right scenarios are examined e.g., through using prototypes in appropriate scenarios or through incidents during practice. Ultimately, we need to explain why this technology-induced complexity occurs so often when designers fully expect these systems to produce major benefits for the practitioners. There are many factors that could be invoked to explain this observation. Some may fall into hoary cliches about the need for human factors in the design process. Others may examine the pressures on development and developers. Here we explore one factor that contributes in part -- a fundamental