Shift

TLDR

Retrieving a stylus on pen‑based devices is slow, so users often tap with bare fingers, which increases targeting times and error rates due to finger occlusion and ambiguous selection points. The authors introduce Shift, a pointing technique designed to mitigate these finger‑related targeting problems. Shift generates a callout that displays a copy of the occluded screen area in a non‑occluded location and a pointer indicating the finger’s selection point, allowing users to guide the pointer into the target by moving their finger and confirming the selection by lifting. A user study shows that Shift reduces error rates for small targets and is faster than Offset Cursor for larger targets, while avoiding callouts for large targets.

Abstract

Retrieving the stylus of a pen-based device takes time and requires a second hand. Especially for short intermittent interactions many users therefore choose to use their bare fingers. Although convenient, this increases targeting times and error rates. We argue that the main reasons are the occlusion of the target by the user's finger and ambiguity about which part of the finger defines the selection point. We propose a pointing technique we call Shift that is designed to address these issues. When the user touches the screen, Shift creates a callout showing a copy of the occluded screen area and places it in a non-occluded location. The callout also shows a pointer representing the selection point of the finger. Using this visual feedback, users guide the pointer into the target by moving their finger on the screen surface and commit the target acquisition by lifting the finger. Unlike existing techniques, Shift is only invoked when necessary--over large targets no callout is created and users enjoy the full performance of an unaltered touch screen. We report the results of a user study showing that with Shift participants can select small targets with much lower error rates than an unaided touch screen and that Shift is faster than Offset Cursor for larger targets.