Abstract
Tablet PCs are gaining popularity, but many individuals still struggle with pen-based interaction. In a previous baseline study, we examined
the types of difficulties younger and older adults encounter when using pen-based input. The research reported in this article seeks to address
one of these errors, namely, missing just below. This error occurs in a menu selection task when a user.s selection pattern is downwardly
shifted, such that the top edge of the menu item below the target is selected relatively often, while the corresponding top edge of the target
itself is seldom selected. We developed two approaches for addressing missing just below errors: reassigning selections along the top edge and
deactivating them. In a laboratory evaluation, only the deactivated edge approach showed promise overall. Further analysis of our data revealed
that individual differences played a large role in our results and identified a new source of selection difficulty. Specifically, we observed
two error-prone groups of users: the low hitters, who, like participants in the baseline study, made missing just below errors, and the high
hitters, who, in contrast, had difficulty with errors on the item above. All but one of the older participants fell into one of these
error-prone groups, reinforcing that older users do need better support for selecting menu items with a pen. Preliminary analysis of the
performance data suggests both of our approaches were beneficial for the low hitters, but that additional techniques are needed to meet the
needs of the high hitters and to address the challenge of supporting both groups in a single interface.
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