Running Head: Milliseconds Matter MILLISECONDS MATTER: AN INTRODUCTION TO MICROSTRATEGIES AND TO THEIR USE IN DESCRIBING AND PREDICTING INTERACTIVE BEHAVIOR Wayne D. Gray & Deborah A. Boehm-Davis Human Factors and Applied Cognitive Program George Mason University Manuscript re-submitted 05/12/00 Last Changed: 05/17/00 13:17 Author Notes Thanks to Wai-tat Fu for constructing and running the button study. Thanks to Franz Hatfield and Eric Jenkins for making the data collected on the target acquisition task available for publication. Thanks to Erik M. Altmann for feedback on earlier versions of this manuscript. The work on this project at George Mason University was supported by a grant to the authors from the Department of Defense (through the Air Force Office of Scientific Research, F49620- 97-1-0353). Additional support to the first author was provided by a grant from the National Science Foundation (IRI-9618833). The data collected for the target acquisition task were collected at Synthetic Environments, Incorporated as part of a Phase II Small Business Innovative Research (SBIR) project under contract F41624-95-C-6012 to the USAF Armstrong Laboratory, Crew Systems Directorate. Correspondence concerning this article should be address to Wayne D. Gray; Human Factors and Applied Cognition Program, George Mason University, MSN 3F5, Fairfax, VA 22030, USA. E-Mail: gray@gmu.edu. 1-703-993-1357. The complete set of models for each participant in the target acquisition task can be found at http://hfac.gmu.edu/~mm. Also available at that site are the CPM-GOMS models for the KEYPRESS-MOVE and CLICK-KEYPRESS families of microstrategies.