ill-defined goals, and rapid change" (Klein, 1997:287). These studies span the theoretical-to-applied spectrum and cover many domains. Klein and colleagues (Klein, 1989, 1994, 1997; Klein et al., 1986) have proposed a particular type of decision making model for these situations, the recognition-primed decision (RPD) model, which incorporates three levels of decisions: (1) "matching," or a simple mapping of a recognized situation to a prescribed decision or action; (2) "diagnosing,'' or iterative probing of the environment until the situation is recognized, followed by a triggering of the prescribed decision or action; and (3) "evaluating" or mapping of a recognized situation to a set of prescribed decisions, followed by selection of the most appropriate decision through a mental simulation. At all these levels, situation assessment (recognition in the RPD nomenclature) plays a critical role, central to all subsequent decisions or actions.

One aspect of situation awareness, which has been referred to as crew awareness, is the extent to which the personnel involved have a common mental image of what is happening and an understanding of how others are perceiving the same situation. The ideas of distributed cognition, shared mental models, and common frame of reference play a role in understanding how groups can be aware of a situation and thus act upon it. Research in distributed cognition (Hutchins, 1990; Sperry, 1995) suggests that as groups solve problems, a group cognition emerges that enables the group to find a solution; however, that group cognition does not reside entirely within the mind of any one individual. Research on shared mental models and common frames of reference suggests that over time, groups come to have a more common image of a problem, and this common image is more or less shared by all participants. What is not known is how much of a common image is needed to enhance performance and what knowledge or processes need to be held in common.

There is currently a great deal of interest in individual and team mental models (Reger and Huff, 1993; Johnson-Laird, 1983; Klimoski and Mohammed, 1994; Eden et al., 1979; Carley, 1986a, 1986b; Roberts, 1989; Weick and Roberts, 1993; Walsh, 1995). Common team or group mental models are arguably critical for team learning and performance (Hutchins, 1990, 1991a, 1991b; Fiol, 1994). However, the relationship between individual and team mental models and the importance of shared cognition to team and organizational performance is a matter requiring extensive research. Although many problems are currently solved by teams, little is known about the conditions for team success.

MODELS OF SITUATION AWARENESS

A variety of situation awareness models have been hypothesized and developed by psychologists and human factors researchers, primarily through empirical studies in the field, but increasingly with computational modeling tools. Because of the critical role of situation awareness in air combat, the U.S. Air Force



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