We describe marking menus, an extension of pie menus, which are well suited for stylus-based interfaces. Pie menus are circular menus subdivided into sectors, each of which might correspond to a different command. One moves the cursor from the center of the pie into the desired sector. Marking menus are invisible pie menus in which the movement of the cursor during a selection leaves an "ink trail" similar to a pen stroke on paper. The combination of a pie menu and a marking menu supports an efficient transition from novice to expert performance. Novices can "pop-up" a pie menu and make a selection, whereas experts can simply make the corresponding mark without waiting for the menu to appear. This article describes an experiment in which we explored both articulatory and cognitive aspects of marking menus for different numbers of items per menu and using different input devices (mouse, trackball, and stylus). The articulatory aspects are how well subjects could execute the physical actions necessary to select from pie marking menus. Articulatory aspects were investigated by presenting one group of subjects with the task of selecting from fully visible menus. Because one feature of marking menus is that users should be able to select from them without seeing the menus (by making a mark), we also ran two groups of subjects with invisible pie menus: one group with an ink trail and one without. These subjects were therefore faced with the task of either mentally representing the menu or associating marks with the commands they invoked through practice. These then are the cognitive aspects to which we refer. Our results indicate that subjects' performance degraded as the number of items increased. When menus were hidden, however, subjects performance did not degrade as rapidly when menus contained even numbers of items. We also found subjects performed better with the mouse and stylus than with the trackball.
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