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CS160 Discussion Session - 7

CS160 Discussion Session - 7. Jingtao Wang 10/17/2008. Administrivia. Midterm Review on next Friday 10/24/2008 No multiple choice, most of the questions will be short Q&As. Witty Exchange. Professor: “Q6. Why is recognition preferred over recall? [3 points]”

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CS160 Discussion Session - 7

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  1. CS160 Discussion Session - 7 Jingtao Wang 10/17/2008

  2. Administrivia • Midterm Review on next Friday 10/24/2008 • No multiple choice, most of the questions will be short Q&As.

  3. Witty Exchange • Professor: “Q6. Why is recognition preferred over recall? [3 points]” • Student: “Why isn’t this test multiple choice? ” • Professor: “Because it’s testing what you know, not helping you fill out the answers… i.e. you’re supposed to have recall.”

  4. Theories of Human Performance • Type of theories and models used in HCI: • Empirical laws • Dynamic models • Explanatory theories When look at low enough level (cognitive / motor),people are the same. can predict performance

  5. Empirical Laws • Quantitative rules that provide predictions • Based on experiments or controlled studies • Sometimes are more “rules of thumb” • Encoded as a quantitative empirical ‘model’, commonly known as a ‘Law’ • Examples: Hick’s Law and Fitts’ Law

  6. W D Example: Pointing Device Evaluation • Real task: interacting with GUI’s • Pointing is fundamental • Experimental task: target acquisition • abstract, elementary, essential (target) (start) D = distance W = target width

  7. Movement Time Index of Difficulty (ID [bits] ) W D Fitts’ Law Paul Fitts, 1954 • Index of Performance (IP ) = ID/MT (bits/s) • Depends on bandwidth and throughput Task difficulty is analogous to information: execution time is interpreted ashuman rate of processing information

  8. IP depends on activity / motor unit * * * * * * * * different way to calculate IP * * * * * * * * * * b = slope IP = 1/b * * * * * * * * * * * * a

  9. 50 years of data Reference: MacKenzie, I. Fitts’ Law as a research and design tool in human computer interaction. Human Computer Interaction, 1992, Vol. 7, pp. 91-139

  10. What does Fitts’ law really model? target width (c) velocity (a) (b) distance

  11. Beyond Pointing: trajectory-based Tasks

  12. D W D/2 D/2 D/N D/N D/N D W From Targets to Tunnels… • 1 goal to pass through: • 2 goals to pass through: • N goals to pass through: •  goals to pass through:

  13. fixed width tunnel: narrowing tunnel: W1 W(x) W2 dx general Steering Law: W(s) ds D c W Steering Law (Accot, 1997)“Beyond Fitts’ Law: Models for trajectory based HCI tasks.”Proceedings of ACM CHI 1997 Conference

  14. Some Results (from Accot, 1997)

  15. How to Leverage Fitts Law to Improve User Interface Design? • Directly changing these two parameters obviously does nothing more than change the size and position of onscreen graphical elements, which are presumably already laid out in a reasonably optimal fashion due in part to the interface designer’s basic appreciation of Fitts’ law. • Prospective Directions • Decrease D • Increase W • Decrease D and Increase W • Leveraging Extra Context Information

  16. Pop-up linear menu Pop-up pie menu Today Sunday Monday Tuesday Wednesday Thursday Friday Saturday Decrease D - 1 Linear Menu vs. Pie Menu

  17. Decrease D - 2 Drag and Pop

  18. Increase W – Dynamically Increaseing the Target Size

  19. Increase W (cursor size) • A Failed attempt – Mac OS X Dock

  20. Increase W – Dynamically Increaseing the Target Size

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