the programmer/modeler must explicitly code all its aspects. Some of the architectures, however, have the capability of inferring details of the situation from other information. This capability obviously reduces the programmer's burden, provided the mechanism is suitable for the application.

Planning

HOS and Micro Saint do not provide a planning function (though presumably the programmer can implement it). Several of the architectures (e.g., MIDAS) have the capability of instantiating general plans based on the specifics of a given situation. ACT-R and Soar models can create new plans. This capability is obviously valuable for some applications; however, for those applications not requiring planning (i.e., where procedures can be initiated in a prespecified way), the development and computational overhead may be undesirable.

Decision Making

HOS does not provide decision making capability, except to account for the time required for the operator to make a decision given certain characteristics of the decision problem. Most of the other architectures provide for knowledge-based decision making, with a few offering Bayesian techniques. Some form of decision making capability seems essential for most military simulations, and architectures such as ACT-R, OMAR, and Soar seem most capable in this regard.

Multitasking

All the architectures permit multitasking in some sense, though ACT-R enforces strict serial execution of tasks with no interruptions allowed. The degree of multitasking varies from that of HOS, which allows only a single cognitive task (with parallel, ballistic body motion possible) to EPIC, which permits any number of concurrent tasks provided resource requirements are not exceeded. From the standpoint of multitasking flexibility, then, architectures such as EPIC and MIDAS appear to offer the greatest potential. However, there is disagreement over the psychological validity of such systems, and architectures such as OMAR that limit the operator to only one task requiring conscious thought may be more realistic. It is clear, however, that interruptability is an important feature; all architectures, except ACT-R, have this feature.

Multiple Human Modeling

In principle, multiple copies of any of the architectures could be integrated to allow modeling of multiple operators. However, only about half of the architectures



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