Acquisition of Animated and Pop-Up Targets

Pop-up targets, such as the items of popup menus, and animated targets, such as the moving windows in Mac OS X Expose, are common in current desktop environments. This paper describes an initial study of pointing on popup and animated targets. Since we are interested in expert performance, we study the situation where the user has previous knowledge of the (final) position of the target. We investigate the effect of the DELAY factor, i.e. the delay before the target pops up (for pop-up targets) or the duration of the animation (for animated targets). We find little difference between the two techniques in terms of pointing performance (time and error), however a kinematic analysis reveals differences in the nature of the pointing movement. We also find that movement time increases with DELAY, but the degradation is smaller when the target is farther away than when it is closer. Indeed, larger distances require a longer movement time therefore the target reaches its destination while the participant is still moving the pointer, providing more opportunity to correct the movement than with short distances. Finally we take into account these results to propose an extension to Fitts' Law that better predicts movement time for these tasks.