One goal for the discipline of human-computer interaction is to go beyond the
specifics of guidelines and build on the breadth of principles to develop tested,
reliable, and broadly useful theories. Of course, for a topic as large as user-interface
design, many theories are needed. Some theories are descriptive and
explanatory; these theories are helpful in developing consistent terminology for
objects and actions, thereby supporting collaboration and training. Some theories
are predictive; these theories enable designers to compare proposed designs
for execution time or error rates.
Another way to group theories is according to motor-task performance (pointing
with a mouse), perceptual activities (finding an item on a display), or cognitive
aspects (planning the conversion of a boldfaced character to an italic one).
Motor-task performance predictions are well established and accurate for predicting
keystroking or pointing times (see Fitts's Law, Section 9.3.5). Perceptual
theories have been successful in predicting reading times for free text, lists, for