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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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slide1

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

mobile vs desktop ui design
Mobile vs. Desktop UI Design
  • Designing UIs for mobile devices is quite different from designing for fixed terminals
  • Different characteristics
mobile applications
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
mobile devices
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
presentation focus
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
why one handed interaction
Why One-Handed Interaction?
  • One hand occupied
  • Attention divided among tasks
  • Unstable environment
  • Two handed use unnatural
slide7

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

suitability for one handed use
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
related work

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

related work10
Related Work
  • Thumb-Based Hardware (cont.)
    • Microsoft’s Ultra-Mobile PC (formerly Project Origami)
related work11
Related Work
  • Thumb-Based Hardware (cont.)
    • Touch key phone

(NTT DoCoMo & Mitsubishi)

direct thumb interaction
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???
target size study
Target Size Study

To develop guidelines for targets that

maximize performance and user preference

during one-handed thumb use on

small touchscreen devices

  • Objective
two phase study 1 2
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
two phase study 2 2
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
phase 1 discrete targets 1 2
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
phase 1 discrete targets 2 2
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
phase 2 serial targets
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
results discrete targets 1 3
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
results discrete targets 2 3
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)

results discrete targets 3 3
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

results serial targets 1 2
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
results serial targets 2 2
Results: Serial Targets (2/2)
  • User Preferences
    • NE region was the most

comfortable

    • Minor differences
discussion
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)
conclusion
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
references
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.
slide27
Thank You!

Questions?