Introduction Th e increasing complexity of advanced human-machine systems makes it necessary for system designers to consider human capabilities and limitations as early as possible in system design. In order to reduce risks associated with poor task design with appropriate tools and methods for task analysis and function allocation, it is important to develop models of human performance and human-system interaction that are comprehensive, computational, science-driven, and

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... Models of human performance and humansystem interaction should be comprehensive to capture the whole range of concurrent perceptual, cognitive, motor, and communication activities of human-system performance (also see Byrne, this handbook). Th ese models should be computational and computerized to allow quantitative and rigorous simulation and analysis of design alternatives and scenarios. Th ese models should be science-driven, with deep roots in and strong connections with cognitive science theories and principles. Th ese 30 Abstract Comprehensive and computational models of human performance have both scientific and practical importance to human-machine system design and human-centered computing. This chapter describes human performance models that are based on queuing and network theories. Queuing-based models and network-based models were initially developed as two separate schools of models, as summarized in the first part of the chapter. Recent work based on queuing networks not only integrates the two schools of models into a unified framework but also allows integration of several other schools of approaches such as symbolic models, as described in the second part of this chapter. Historically, the fi rst groups of computational models that examine human performance and the 31_JohnDLee_Ch30.indd 451 31_JohnDLee_Ch30.indd 451