The Reciprocal Nature of Fitts’ Law in Space and Time

Tsung Yu Hsieh, Yeou Teh Liu*, Karl M. Newell

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Human movement takes place in both space and time so that measures of movement accuracy in space are made with respect to time, and vice-versa providing a foundation to the proposal of the complementarity of spatial and temporal error in aiming movements. We examined this hypothesis in both the standard Fitts and Peterson discrete movement speed-accuracy protocol that requires moving to stop within a fixed spatial target (distance (D) with target bandwidth (WD) in an emergent movement time (T) and, also in the reciprocal and novel space-time protocol introduced here that required moving for a fixed temporal target goal T with bandwidth of WT with an emergent D. Experiment 1 examined a range of D conditions (45, 100, 180, 280, and 405 mm with bandwidth WD ±5 mm) within the Fitts’ Law discrete spatial accuracy protocol to provide compatible spacetime boundary conditions for the reciprocal spacetime protocol in Experiment 2 that examined the effect of target time (T − 250, 460, 670, and 880 ms each with bandwidth WT ±50 ms) on the emergent D. The findings showed that the spatial and temporal error profiles in Experiment 2 were consistent with exchanging D and T in Fitts’ Law Equation. This provides evidence for the reciprocal nature of the spacetime error functions in Fitts’ type movement aiming protocols and is compatible with the reciprocal profiles of spatial and temporal errors in other classes of movement aiming tasks.

Original languageEnglish
Pages (from-to)162-173
Number of pages12
JournalJournal of Motor Behavior
Issue number2
Publication statusPublished - 2023


  • discrete movement
  • movement time
  • speed and accuracy tradeoff
  • temporal constraint

ASJC Scopus subject areas

  • Biophysics
  • Orthopedics and Sports Medicine
  • Experimental and Cognitive Psychology
  • Cognitive Neuroscience


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