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Pekka Parhi Department of Electrical and Information Engineering University of Oulu pekka.parhi@ee.oulu.fi Wireless Citi

DESIGN ASPECTS OF MOBILE USER INTERFACES Pekka Parhi Department of Electrical and Information Engineering University of Oulu pekka.parhi@ee.oulu.fi Wireless Cities 2006 Oulu, Finland Mobile vs. Desktop UI Design

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Pekka Parhi Department of Electrical and Information Engineering University of Oulu pekka.parhi@ee.oulu.fi Wireless Citi

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  1. DESIGN ASPECTS OFMOBILE USER INTERFACES Pekka Parhi Department of Electrical and Information Engineering University of Oulu pekka.parhi@ee.oulu.fi Wireless Cities 2006 Oulu, Finland

  2. Mobile vs. Desktop UI Design • Designing UIs for mobile devices is quite different from designing for fixed terminals • Different characteristics

  3. Mobile Applications • Context of use • Dynamic, unpredictable • Often crowded and noisy • User’s attention divided among several tasks • Supported activities • Frequent, short-duration, immediate • Focused: few specific tasks can be carried out very well

  4. Mobile Devices • Physical issues • Limited screen space • Limited input capabilities • Simple interaction • Awkward text entry • Technical issues • Processing power, memory, storage space, battery life • Challenges with wireless networking • Slow, intermittent connection

  5. Presentation Focus • One-handed interaction • UI design to support one-handed use of mobile devices • Target size study for one-handed thumb use on touchscreen devices

  6. Why One-Handed Interaction? • One hand occupied • Attention divided among tasks • Unstable environment • Two handed use unnatural

  7. Interaction on Existing Handhelds • Smartphones • Input: Hardware Buttons • Interaction: Keypad-mapped functions Directional navigation • PDAs • Input: Touch Sensitive Display Hardware Buttons • Interaction: Software targets for direct manipulation Directional navigation

  8. Suitability for One-Handed Use? • Smartphones • Touchscreens offer greater flexibility for UI design • UIs traditionally designed for pen-based, two-handed interaction • Compact form, proper-sized keys • Interaction limited to keypad mapped menus and directional navigation • Not efficient nor user-friendly Touchscreen UIs for one-handed interaction? • PDAs

  9. MessagEase LaunchTile Apple iPod Jackito PDA Related Work • Interfaces for One-Handed Use on PDAs • AppLens & LaunchTile [Karlson 2005] • Command-Based Gestures • Direct Manipulation Gestures • MessagEase[Nesbat 2003] • Scalable Keypad for Text Entry • Thumb-Based Hardware

  10. Related Work • Thumb-Based Hardware (cont.) • Microsoft’s Ultra-Mobile PC (formerly Project Origami)

  11. Related Work • Thumb-Based Hardware (cont.) • Touch key phone (NTT DoCoMo & Mitsubishi)

  12. Direct Thumb Interaction • Limited Screen Space • UI targets should be as small as possible without degrading performance and user satisfaction • No previous target size studies for one-handed use on small touchscreen devices • Studies exist for desktop-sized displays and pen-based interaction on mobile devices • Optimal Size for Targets???

  13. Target Size Study To develop guidelines for targets that maximize performance and user preference during one-handed thumb use on small touchscreen devices • Objective

  14. Two-Phase Study (1/2) Phase 1: Discrete Targets • Single-target selection tasks • Similar to clicking a button or selecting a menu option Phase 2: Serial Targets • Multi-target selection tasks • Similar to text entry

  15. Two-Phase Study (2/2) • Participants • 20 (17 Male, 3 Female) • 18 regular cell phone users • 6 regular PDA users • All right-handed • HP iPAQ Pocket PC used • Tasks performed standing • Total time: 40-45 minutes • Including instruction, both phases and questionnaires

  16. Phase 1: Discrete Targets (1/2) • 5 target sizes (3.8, 5.8, 7.7, 9.6, 11.5 mm) • 9 locations (screen divided into a 3x3 grid) • Each target size tested 5 times per location

  17. Phase 1: Discrete Targets (2/2) • (1) tap green button, (2) tap actual target ‘x’ • North <> South movement • Measures • speed, accuracy, hits distribution, user preferences • Constant distance between green button and target ‘x’ • X surrounded by ‘distractors’ • Lift-off selection strategy • Auditory and visual feedback

  18. Phase 2: Serial Targets • 5 target sizes (5.8 – 13.4 mm), 4 locations • (1) Tap green, (2) Enter 4-digit code, (3) Tap END • Measures • speed, accuracy, user preferences

  19. Results: Discrete Targets (1/3) • Speed • Differences between all sizes were statistically significant • Error Rate • No difference between 9.6 and 11.5 mm target sizes • Significant differences between other sizes • Location had no effect on either speed or accuracy

  20. Results: Discrete Targets (2/3) • Hits Distribution • Hit area increased with target size • Users trade off speed for tap accuracy • Right-leaning trend for targets on the right side (white boxes = buttons; dark gray boxes = area enclosing 95% of hits per location; gray dots = successful hits; black dots = erroneous hits)

  21. Results: Discrete Targets (3/3) • User Preferences • Centerregion was the easiest • Objects on the left side and bottom right corner were the hardest Mean comfort rating for each region (1-7; 7 = most comfortable) Mean of the smallest comfortable target size in the region

  22. Results: Serial Targets (1/2) • Speed • Differences between all sizes were statistically significant • Error Rate • 5.8 mm differed significantly from target sizes ≥ 9.6 mm • No difference between other target sizes • Location had no effect on either speed or accuracy

  23. Results: Serial Targets (2/2) • User Preferences • NE region was the most comfortable • Minor differences

  24. Discussion • Speed continued to improve significantly with even the largest targets in both phases • No difference in error rates with target sizes ≥ 9.6 mm (discrete) and ≥ 7.7 mm (serial) • Error rates were much higher in serial tasks than in discrete tasks (9.6 mm target: 5.0% vs. 2.8%) • Limitations of the study • One posture used for performing tasks (standing) • One touchscreen-equipped mobile device (PDA)

  25. Conclusion • Target size recommendations for one-handed use of touchscreen-based handhelds • ≥ 9.2 mm for single-target pointing tasks • ≥ 9.6 mm for multi-target pointing tasks • Recommendations based on error rates data along with user preferences • As well as hits distribution data for single-target tasks

  26. References • Parhi P, Karlson A, Bederson B (2006) Target Size Study for One-Handed Thumb Use on Small Touchscreen Devices. Proc. MobileHCI ’06, Espoo, Finland, to appear. • The presented study was done in UMD during Fall 2005.

  27. Thank You! Questions?

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