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Shift

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Description

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.




Errata

  • "Apparatus", Page 7: The IPAQ 4100 PDA display dimensions are 55.0 x 73.3 mm with an effective resolution of 4.36 px/mm.
  • "Design", Page 4: The final design uses a circular frame 16mm in diameter (70 px). Note that the callout distance is correct in the paper: it is 22mm above the initial touch point. As a clarification, this is from the contact point to the centre of the callout.
  • "Zooming", Page 9: We increase the callout diameter from 16mm to 30mm.
  • "Pointer Stabilization", Page 6 The dynamic recursive low pass filter interpolation values are correct in the paper: between 150 and 560 mm/s. However, at 04:00 in the accompanying Video, the "Filter" settings tab should show the corresponding Velocity High and Velocity Low units as mm/s.