ABSTRACT
Our purpose in this chapter is to convey a version of the existing psychological science base in a form suitable for analyzing human-computer interaction. To be practical to use and easy to grasp, the description must necessarily be an oversimplification of the complex and untidy state of present knowledge. Many current results are robust, but second-order phenomena are almost always known that reveal an underlying complexity; and alternative explanations usually exist for specific effects. An uncontroversial presentation in these circumstances would consist largely of purely experimental results. Such an approach would not only abandon the possibility of calculating parameters of human performance from the analysis of a task, but would also fail in the primary purpose of giving the reader knowledge in a form relatively easy to assimilate.
