TiltText: Using Tilt for Text Input to Mobile Phones Daniel Wigdor & Ravin Balakrishnan

2 Text Messaging Estimated 500,000,000,000 text messages in 2003 worldwide More popular outside North America

3 Ambiguity Pressing “2” : {2,a,b,c,A,B,C}

4 Solutions MultiTap Language-based disambiguation T9 Letterwise Wordwise Alternate Layouts:

5 MultiTap: ~2.1 KSPC e.g.: {6,6,6,>,6,6} = “on”

6 T9: ~1.2 KSPC e.g.: {6,6} = “on”, “no”, “mo”,…

7 T9: Problems Ambiguity persists Inconsistent Eyes-free operation impossible Only English-Like text No numerals Real “texting” impossible (“b4”,”btw”,”lol”,”rotflmao”…)

8 What’s best? Low KSPC Eyes-free Non-language specific

9 Tilt as input Add a tilt sensor to device inexpensive accelerometers Hinckley et al. UIST’00 Tilt for text input: Sazawal et al. Unigesture MobileHCI ‘02 Partridge et al. TiltType UIST’02 No formal evaluations

10 TiltText: 1 KSPC + Tilt Action eg: {7} = … P Q R S

11 Tilt Detection: Key Tilt Difference between press & release Slow: 3 consecutive actions keypress, tilt, key-release Pilot study: poor performance

12 Tilt Detection: Absolute Relative to a fixed origin Keypress & tilt actions concurrent Consecutive same-tilt: savings Consecutive opposite-tilt: extra cost High error-rate: “creeping posture”

13 Tilt Detection: Relative Most recent tilting gesture floating origin Maintains advantages of Absolute tilt Saves work on consecutive same tilts & consecutive opposite tilts No “creeping posture”

14 Our Prototype Uses Absolute tilt Tilts from board via serial port

15 The Study Repeated-measures design 10 participants 2 techniques (MultiTap & TiltText) 16 blocks of 20 phrases each in 2 sessions Same phrases for both techniques Technique order between participant Measured time & accuracy Participants told to correct mistakes

16 Results: Overall Speed Overall, TiltText 16% faster (including error correction) Block WPM

17 Power-law extrapolation WPM Block

18 Results: Between Participant Data from 1 st technique seen by each participant TiltText still faster Block WPM

19 Results: Error Rate TiltText error rate higher than MultiTap Error Rate Percentage Block

20 Error Rate: By Letter Error rates much higher for some letters Correct Letter Error Rate Percentage

21 Error Rate: Tilt Direction Direction significantly effects error rate Creeping posture Error Rate Percentage Correct Tilt Direction

22 Conclusions Implemented TiltText Three distinct approaches for tilt Formal study conducted TiltText faster despite errors

23 Future Work Theoretical TiltText speed KSPC is not the whole story Implement relative-tilt system Deeper analysis of error causes Longer study Optimizing letter/key assignments

24 Acknowledgements Michael McGuffin Richard Watson DGP Lab members Study participants Microsoft Research

25