Acknowledgments
My interest in man-machine communication was awakened while working on the PLATO project at the
University of Illinois, to which I owe many insights. The experimental systems XS-0 and XS-1 served as
test beds for evaluating the design techniques presented in this paper. I am indebted to my co-workers on
these projects, in particular to G. Beretta, H. Burkhart, P. Fink, B. Plattner, J. Stelovsky, H. Sugaya, A.
Ventura, and J.Weydert. This is a revised version of a paper presented at the 1982 International Zurich
Seminar on Digital Communications, MAN-MACHINE INTERACTION, March 9-11, 1982.