What is the person trying to accomplish?
Outcome before interface.
Tasks should be understood in the user’s context rather than as screen operations alone.
Side 59
Human–Computer
Interaction
A study of the boundary between people and computational systems. HCI asks how goals become actions through interfaces, and how feedback, constraints and representation shape usability and understanding.
user→goal→interface→action→feedback
06interaction lenses
05usability dimensions
05evaluation methods
59Side
Interaction is a loop between intention and system response.
Users form goals, choose actions, observe feedback and update their mental model.
Can the user see what actions are possible?
Affordance + signifier.
Visible cues reduce guessing.
Can intention be translated into input?
Control mapping.
Interaction should make the relationship between action and effect understandable.
What did the system do?
Visible state change.
Fast feedback closes the loop and reduces uncertainty.
Can the user explain the result?
Mental model.
Good interfaces help users predict what will happen next.
Interfaces compete for finite attention and memory.
Visual grouping, recognition and external representation can reduce cognitive work.
Selective processing.
Salience should direct attention toward what matters, not decorative noise.
Easier than recall.
Visible choices reduce memory burden compared with memorized commands.
Group related information.
Structure helps users process many elements as fewer meaningful units.
Reuse learned patterns.
Consistent interaction reduces relearning and prediction error.
Controls should correspond to effects.
Natural mappings reduce interpretation burden.
People will make mistakes.
Design should prevent, detect and recover rather than merely blame.
Interface design makes system state legible.
Hierarchy, feedback and constraints help users understand what can happen and what has happened.
Hierarchy
Make importance visible.
Layout and typography should reflect task priority.
Constraint
Prevent invalid action.
Disable or remove impossible options when the system already knows they cannot work.
Feedback
Show state change immediately.
Loading, saved and error states should be explicit.
Reversibility
Let users undo risky actions.
Reversible operations encourage exploration and reduce fear.
Progressive disclosure
Reveal complexity when needed.
Advanced options need not burden first-time use.
Usability is multidimensional.
A system can be easy to learn yet inefficient for experts, or fast yet error-prone.
| Dimension | Question | Signal |
|---|---|---|
| Learnability | How quickly can a new user begin? | Time to first successful task |
| Efficiency | How much effort after learning? | Time / actions per task |
| Errors | How often and how severe? | Error rate + recovery success |
| Memorability | Can occasional users return? | Relearning burden |
| Satisfaction | How does interaction feel? | Reported confidence / frustration |
Accessible interaction broadens who can use the system.
Accessibility is a design constraint across perception, motor control, cognition and assistive technologies.
Do not rely on sight alone.
Semantic structure, contrast and text alternatives support diverse vision.
Do not rely on audio alone.
Captions and visual equivalents preserve information.
Support varied input precision.
Keyboard access and sufficiently large targets reduce motor demands.
Reduce unnecessary complexity.
Clear language and predictable structure support comprehension.
Expose semantics, not only pixels.
Screen readers and alternative input need structured interfaces.
Disability can be situational.
Glare, noise, injury or divided attention can create temporary access barriers.
Interfaces should be tested with behavior, not only taste.
Evaluation combines observation, measurement and user explanation.
Usability test
Watch representative users attempt realistic tasks.
Think aloud
Ask users to verbalize interpretation while interacting.
Heuristic review
Inspect the interface against established interaction principles.
Analytics
Measure completion, abandonment, latency and repeated failure at scale.
Experiment
Compare interface variants when the outcome can be measured reliably.
The Design of Everyday ThingsDon Norman · action and feedback
Human–Computer InteractionDix et al. · broad foundation
About FaceCooper et al. · interaction design
Designing with the Mind in MindJeff Johnson · cognition and interface design