rmh: fitts’ law paul cairns [email protected]
TRANSCRIPT
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?
T a b.log 2
2DW
ARMH: Fitts' Law
Theory (or Analogy?)
Analogy with Shannon information
Meyer’s derivation MacKenzie’s improvement
C B.log 2
S NN
T a b.log 2
D WW
ARMH: Fitts' Law
Terms
Index of difficulty– bits
Index of Performance, 1/b– bits per second
ID log2D WW
log2DW
1
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), 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