This paper presents the results of a study to gather information on the underlying causes of pen -based target acquisition difficulty. In order to observe both simple and complex interaction, two tasks (menu and Fitts' tapping) were used. Thirty-six participants across three age groups (18-54, 54-69, and 70-85) were included to draw out both general shortcomings of targeting, and those difficulties unique to older users. Three primary sources of target acquisition difficulty were identified: slipping off the target, drifting unexpectedly from one menu to the next, and missing a menu selection by selecting the top edge of the item below. Based on these difficulties, we then evolved several designs for improving pen-based target acquisition. An additional finding was that including older users as participants allowed us to uncover pen-interaction deficiencies that we would likely have missed otherwise.


Figure 1: Screen shots mid-trial: (a) the multi-dimensional tapping task, (b) the menu task (note, the 'start' target is occluded by the screen shot of the tapping task).
Figure 2: Tapping task results, by age group: (a) mean trial time (N = 35), (b) mean errors for slips & near misses (N = 36).
Figure 3: Drifting results, by age group: (a) mean trial time, without & with drift (N = 35), (b) mean drifts (N = 33).
Figure 4: Histogram of the vertical position of tap ups occurring on the target item and the item below (N = 5045).


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