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, Volume 4, Issue 2, pp 85–95 | Cite as

Movement time for motion-impaired users assisted by force-feedback: effects of movement amplitude, target width, and gravity well width

  • Faustina Hwang
  • Simeon Keates
  • Patrick Langdon
  • P. John Clarkson
Long paper


This paper presents a study investigating how the performance of motion-impaired computer users in “point and click” tasks varies with target distance (A), target width (W), and force-feedback gravity well width (GWW). Six motion-impaired users performed “point and click” tasks across a range of values for A, W, and GWW. Times were observed to increase with A, and to decrease with W. Times also improved with GWW, and, with the addition of a gravity well, a greater improvement was observed for smaller targets than for bigger ones. It was found that Fitts’ Law gave a good description of behaviour for each value of GWW, and that gravity wells reduced the effect of task difficulty on performance. A model based on Fitts’ Law is proposed, which incorporates the effect of GWW on movement time. The model accounts for 88.8% of the variance in the observed data.


Fitts’ Law Motion-impaired Force-feedback Haptic 



The authors thank the volunteers and staff of the Papworth Trust. We also wish to thank one particular reviewer for a detailed and helpful review. This work is funded by the Canadian Cambridge Trust, NSERC, and the EPSRC.


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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • Faustina Hwang
    • 1
  • Simeon Keates
    • 2
  • Patrick Langdon
    • 1
  • P. John Clarkson
    • 1
  1. 1.Department of EngineeringUniversity of CambridgeCambridgeUK
  2. 2.IBM T.J. Watson Research CenterHawthorneUSA

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