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RMH: Fitts’ Law

RMH: Fitts’ Law. Paul Cairns paul.cairns@york.ac.uk. A law?!?!. One of the few in HCI Predictive Reliable Valuable research tool!. Today’s objectives. Fitts’ Law Theoretical basis Adaptations for HCI Implications for design Thoughts on modelling. Overview. Model for prediction

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RMH: Fitts’ Law

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  1. RMH: Fitts’ Law Paul Cairns paul.cairns@york.ac.uk

  2. A law?!?! • One of the few in HCI • Predictive • Reliable • Valuable research tool! ARMH: Fitts' Law

  3. Today’s objectives • Fitts’ Law • Theoretical basis • Adaptations for HCI • Implications for design • Thoughts on modelling ARMH: Fitts' Law

  4. Overview • Model for prediction • Time to point • Difficulty of target ARMH: Fitts' Law

  5. A demo Interactive Fitts' Law talk • Not quite accurate! ARMH: Fitts' Law

  6. Fitts’ Proposed Law • D • 1/W • a, b • Log? ARMH: Fitts' Law

  7. Theory (or Analogy?) • Analogy with Shannon information • Meyer’s derivation • MacKenzie’s improvement ARMH: Fitts' Law

  8. Terms • Index of difficulty • bits • Index of Performance, 1/b • bits per second ARMH: Fitts' Law

  9. Impact in HCI • Reduce ID • Bigger icons, more space • Compare IP • “Capacity” of input devices • Put things in edges and corners ARMH: Fitts' Law

  10. Deconstructing Fitts • Ecological validity • Construct validity ARMH: Fitts' Law

  11. What Fitts did: W D ARMH: Fitts' Law

  12. Let’s have a go! ARMH: Fitts' Law

  13. What we apply it to: ARMH: Fitts' Law

  14. Correcting for W • W’ – actual cross-section • Smaller of W and H • Area, W x H • Sum, W + H • Stick with W • Which is best? ARMH: Fitts' Law

  15. Implications debunked • Edges are better • Corners are best • What about closeness of targets? • Mice are non-linear anyway! ARMH: Fitts' Law

  16. What remains? • D/“W” is key • Target size (angle) • Stopping range (proportion) • Non-linear (concave), monotonic • Quite possibly log function • IP is meaningful • a is important ARMH: Fitts' Law

  17. Toolbars • This is annoying not useful • Edges and corners? ARMH: Fitts' Law

  18. Novel interactions • Artificially increasing W • “Sticky” buttons • Bubbles • Changing select • Goal-crossing ARMH: Fitts' Law

  19. Novel devices • Comparing IP • iPhone • Wii • Kinect • Eye Gaze ARMH: Fitts' Law

  20. Thoughts on Modelling • Is it a good model? • Yes, it fits the data • No, we don’t know why! • Could we produce a better one? • How? ARMH: Fitts' Law

  21. Advanced Fitts’ Law • Fitts’ law as a model • Steering law • Games • Menu navigation • VE/VR? ARMH: Fitts' Law

  22. Reading for today • MacKenzie (1992) Fitts’ Law as a Research and Design Tool…, HCI (7), 91-139 • MacKenzie & Buxton (1992) Extending Fitts’ Law to 2d tasks, CHI 1992, 219-226 • Interaction Design, 2nd edn • Cockburn & Firth (2003) Improving the acquisition of small targets. BCS HCI 03, 181-196 • Accot & Zhai (1997) Beyond Fitts’ Law… ACM CHI 97, 295-302 ARMH: Fitts' Law

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