MAKING MARKS SELF-REVEALING

A good interface is easy to use for both a novice and an expert user. For example, menu-driven interfaces are best for novices because they make explicit which commands are available. However expert users know the command set and thus prefer to have "short cuts" for invoking commands. Accelerator keys on keyboards are one example of giving experts short cuts. In pen-driven systems, markings can be used instead of accelerator keys.Usually there is a dramatic difference between novice and expert behavior at the level of physical action. For example, a novice may use a mouse to select from a men u whereas an expert may press an accelerator key. My goal is to reduce the discrepancy between actions without compromising efficiency for the expert and ease of learning for the novice. When the basic action of the novice and expert are the same, novice performance develops the skills necessary for expert performance, smoothing the transition from novice to expert.With this goal in mind, I have designed and implemented an interaction technique in which pie menus provide away of showing users the association between markings and commands they can invoke in pen-based interfaces. By adding a virtual ink trail to the path of the cursor, markings become the natural by-products of the strokes necessary to select a sector from a subdivided circular menu (or "pie").Figure 1 illustrates this technique in the context of creating three simple objects. An expert uses simple shorthand marks to create and place circles, square, or triangles. Object creation and placement is thus fast and efficient. Figure 2 shows how a novice, unsure of what marks to use, can pop-up a pie menu of these objects by keeping the pen pressed. The desired object can then be selected. It is critical to note that selection from the menu constitutes the same physical action as making the corresponding mark for that object. The novice is thus rehearsing the physical action used by an expert.An experiment to evaluate this technique revealed that markings could be used for selecting up to 5 items quickly and accurately. Adding more items is possible whe n metaphors are used to help the user remember mark/menu-item associations For example, the clock-face metaphor was found to be particularly useful. Finally it was found that with very little practice users' performance becam e substantially faster and less error-prone.