which can be added in modular fashion to the basic ACT-R system. Both ACT-R and ACT-R/PM are currently available only for the Macintosh, but there are plans to port them to the Windows platform or to some platform-independent format, such as CLIM.

The basic system and the additional tools are fully documented, and manuals are available both in MS Word and over the World Wide Web. The Web manuals are integrated using a concept-based system called Interbook, with a tutorial guiding beginners through the theory and practice of ACT-R modeling in 10 lessons. The Web-based tutorial is used every year for teaching ACT-R modeling to students and researchers as part of classes at Carnegie Mellon University (CMU) and other universities, as well as summer schools at CMU and in Europe. The yearly summer school at CMU is coupled with a workshop in which ACT-R researchers can present their work and discuss future developments. The ACT-R community also uses an electronic mailing list to announce new software releases and papers and discuss related issues. Finally, the ACT-R Web site (http://act.psy.cmu.edu) acts as a centralized source of information, allowing users to download the software, access the Web-based tutorial and manuals, consult papers, search the mailing list archive, exchange models, and even run ACT-R models over the Web. The latter capacity is provided by the ACT-R-on-the-Web server, which can run any number of independent ACT-R models in parallel, allowing even beginners to run ACT-R models over the Web without downloading or installing ACT-R.

Validation

ACT-R has been evaluated extensively as a cognitive architecture against human behavior and learning in a wide variety of tasks. Although a comprehensive list of ACT-R models and their validation is beyond the scope of this chapter, the most complete sources of validation data and references to archival publications are Anderson's series of books on the successive versions of ACT (Anderson, 1983, 1990, 1993; Anderson and Lebiere, 1998). The latter reference also contains a detailed comparison of four cognitive architectures: ACT-R, executive-process interactive control (EPIC), Soar, and CAPS (a less well-known neural-cognitive architecture not reviewed here).

Applicability for Military Simulations

The vast majority of ACT-R models have been for relatively small problem solving or memory tasks. However, there is nothing in principle that prevents ACT-R from being applicable to military simulations. There may be some problems associated with scaling up the current implementation to extremely large tasks that require extensive knowledge (only because the architecture has not been pushed in this manner), but any efficiency problems could presumably be



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