RMH: Fitts’ Law Paul Cairns

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

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

ARMH: Fitts' Law Overview  Model for prediction  Time to point  Difficulty of target

ARMH: Fitts' Law A demo Interactive Fitts' Law talk – Not quite accurate!

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

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

ARMH: Fitts' Law Terms  Index of difficulty – bits  Index of Performance, 1/b – bits per second

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

ARMH: Fitts' Law Deconstructing Fitts  Ecological validity  Construct validity

ARMH: Fitts' Law What Fitts did: D W

ARMH: Fitts' Law Let’s have a go!

ARMH: Fitts' Law What we apply it to:

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

ARMH: Fitts' Law 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 Toolbars  This is annoying not useful  Edges and corners?

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

ARMH: Fitts' Law Novel devices  Comparing IP – iPhone – Wii – Kinect – Eye Gaze

ARMH: Fitts' Law 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 Advanced Fitts’ Law  Fitts’ law as a model  Steering law – Games – Menu navigation – VE/VR?

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