Responsiveness

• Adapts to different window sizes and/or devices
• Delivers feedback in a timely manner

Possible Improvement

• Loading data efficiently so it's available quickly
• Designing for human perception of time

Factors

• User expectations
• Application and Interface Design
  • The interface keeps up with user actions
  • The interface informs the user about application status
  • The interface doesn't
• Responsiveness is the most important factor in determining user satisfaction
  • Not neccesarily system performance

Slow Performance but Responsive

• Provide feedback to confirm user actions
• Provide feedback about what is happening (e.g. progress bars)
• Allow users to perform other tasks while waiting
• Anticipate users' most common requests
• Performs housing keeping and low-priority tasks in the background

Perceived Time

• The duration of perceptual and cognitive processes
• Helps with responsive design

• Visual stimulus (second row)
  • Continous input latency should be less than 10ms
• Cause-effect events (fourth row)
  • If UI feedback takes longer than 140ms to appear, the perception of "cause and effect" is broken

Design Implications

• Visual-motor reaction time for unexpected events
  • Display busy/progress indicators for operations more than 1s
• Time to prepare for conscious cognition task
  • Display a fake version (preview) of an application interface, while the real one loads (< 10s)

Responsive Design Methods

Designing a Progress Indicator

• Show work remaining as well as work completed
• Show total progress when multiple steps, not only step progress
• Display finished state (e.g. 100%)
• Show smooth progress (not erratic burests)
• Use human precision (about 4 minutes rather than 243.5 seconds)

Tweaking Progress Bars

• Can improve responsiveness by tweaking the mapping from actual progress to displayed progress

Progressive loading

• Provide user with some data while loading rest of data
• e.g. Incremental search, image rendering from low to high resolution etc.

Predicting Next Operation

• Use periods of low load to pre-compute responses to high probability requests
• e.g. Lookahead for the next occurence of the target word while user lookks at the current; web browser pre-download linked pages

Graceful Degradation of Feedback

• Simplify feedback for high-computational tasks
• E.g. Window only updates after drag; reduced render quality when panning or zooming etc.

Chuncking Process

• Avoid doing frequent processing during user interaction
• E.g. validate after pressing ENTER, not character by character; don't send data to server unti lafter direct manipulation action