Abhishek Nandakumar
December 11, 2012
590

# Breaking Fitts's Law

## Abhishek Nandakumar

December 11, 2012

## Transcript

1. Breaking Fitts’s Law

2. Is it faster to click on
targets at the edge of
the screen?

3. 1680 x 1080

4. Bounding line simulates edge of screen

5. Bounding line simulates edge of screen

6. Theoretical Underpinnings:
Targets at the edge of the screen
effectively have inﬁnite width

7. W = ∞

8. W

9. Are movement times lower while
selecting targets at the edge of the screen
than predicted by Fitts’ law?
Objectiﬁed Question

10. Does the magnitude of effect vary based
on target size?

11. Bounded mouse movements will be
faster than Fitts’ Law would predict.
Hypothesis 1

12. Bounded mouse movements will be
faster than identical unbounded
movements.
Hypothesis 2

13. Simulate the edge of the screen with a
‘bounding box.’
Participants perform an identical set of
pointing tasks with a bounding box and
without one.
Design

Screen Resolution Consistent at 1680x1080
Subject Distance from Screen Same chair height and distance from monitor
Type of Mouse Use of identical Dell optical mouse
Order of Trials Randomized trials to eliminate order effects
Device LCD with identical calibration and constrast
Starting Position Always in the center of the screen

15. Methodology
1680x1080 Resolution
22” Display
2 Foot distance from Display
Targets are 1º and 1.2º of Visual Angle
Dell optical mouse
Randomized order of trials
10 second break after 25 trials to reduce fatigue
Bright green targets on black background
Pink bounding border
Trial time = Time from start until successful click
0.5s ﬁxation time as cursor is auto-centered.
Cursor always starts at center of screen
8 varying target distances
Two distinct target sizes
Same set of targets
4 participants

16. We used the Least-of method of determining target with
in two-dimensions, which MacKenzie and Buxton (1992)
found to be comparable to the W’ Model (actual target
depth along the approach vector).

17. t=-5.7272
p<0.05
t=0.1196
p=0.9
t=-7.8984
p<0.05
Condition
Average (Observed MT)
Average Observed MT vs. Condition

18. Correlation
No Bounding Box Bounding Box
0.9
0.7
0.5
0.3
0.1

19. Differences of Observed Time and Predicted Time

20. Data
Observed MT vs. Predicted MT (Large targets with Bounding Box)

21. Data
Observed MT vs. Predicted MT (Large Targets with No Bounding Box)

22. Data
Observed MT vs. Predicted MT (Small targets with Bounding Box)

23. Data
Observed MT vs. Predicted MT (Small Targets with No Bounding Box)

24. Independent Variables:
Presence of Bounding Line
Size of Target
Dependent Variable:
Observed Movement Time

25. ★ Perform test on tablet with physical bounding
boxes
★ Test sizes between 20px and 100px to ﬁnd out
when size becomes insigniﬁcant.
★ Test for External Validity
★ Compare differences in accessibility of tabs
between browsers:
★ Chrome on Windows and Mac OS X
★ Chrome and Firefox
Next Steps