Human-Computer Interaction (HCI) is a multidisciplinary field that studies how people interact with computers and designs systems to be more user-friendly, efficient, and accessible. It draws from computer science, psychology, design, and sociology.
| Element | Description |
|---|
| Users | The people who interact with the system |
| Tasks | The goals users want to accomplish |
| Interface | The point of interaction (screen, keyboard, voice, etc.) |
| Environment | The physical and social context of use (lighting, noise, setting) |
Usability measures how effectively, efficiently, and satisfactorily a user can achieve their goals with a system. Its five key components are:
- Learnability — How easy is it for new users to learn the system?
- Efficiency — How quickly can experienced users perform tasks?
- Memorability — Can users return after a break and remember how to use it?
- Error Handling — How well does the system prevent errors and help users recover?
- Satisfaction — How pleasant is the experience?
- UI (User Interface): The specific visual and interactive elements users interact with — buttons, menus, screens, icons.
- UX (User Experience): The overall feeling, emotion, and efficiency a user experiences while using the entire system.
UI is what you interact with; UX is how that interaction makes you feel.
- Cognitive overload — Too much information presented at once overwhelms users.
- Poor feedback — System does not inform users whether their action succeeded or failed.
- Inconsistency — Different parts of the interface behave differently, confusing users.
- Accessibility barriers — Interfaces that exclude users with disabilities (visual, motor, cognitive).
- Error-prone design — Layouts that make it easy to click the wrong button.
- Long learning curves — Non-intuitive designs that require extensive training.
A design philosophy that places end-users at the core of the design process. It is iterative: designers repeatedly prototype, test with real users, gather feedback, and refine the product.
UCD Cycle:
- Understand user needs
- Design prototype
- Test with users
- Analyse feedback
- Refine → repeat
- Usability testing — Observing real users attempting real tasks.
- Heuristic evaluation — Experts review the interface against established usability principles (Nielsen's 10 heuristics).
- Accessibility audits — Checking compliance with standards like WCAG (Web Content Accessibility Guidelines).
- A/B testing — Comparing two design variants to see which performs better.
- Prototyping — Building low-fidelity (paper) or high-fidelity (digital) mockups before full development.
| Issue | Explanation |
|---|
| Dark patterns | Deceptive UI designs that trick users into unintended actions (e.g., hidden unsubscribe buttons) |
| Privacy | Systems that collect excessive user data without informed consent |
| Addiction by design | Infinite scroll, notifications engineered to maximise screen time at the cost of user wellbeing |
| Bias in design | Interfaces designed without considering diverse user groups, excluding minorities |
| Informed consent | Users must understand what they agree to — complex terms of service violate this principle |
- Digital divide — Poor HCI design can exclude elderly, disabled, or low-literacy users from digital services.
- Social isolation — Poorly designed social platforms can increase loneliness rather than connection.
- Behavioural change — Persuasive technology (likes, streaks) shapes social behaviour and norms.
- Accessibility and inclusion — Good HCI design promotes equal participation in digital society.
- Productivity gains — Well-designed interfaces reduce time-on-task and training costs for organisations.
- E-commerce conversion — Poor UX directly reduces sales; good UX increases revenue.
- Cost of poor design — Fixing usability problems after launch is far more expensive than designing correctly from the start.
- Job displacement — Automation enabled by better HCI (voice assistants, kiosks) can reduce demand for certain roles.
- Energy consumption — Poorly optimised interfaces (e.g., auto-playing video) increase device and server energy use.
- E-waste — Devices become obsolete faster when software updates make older hardware unusable (planned obsolescence).
- Paperless design — Good digital HCI can reduce paper consumption in offices and education.
- Green UX — Designing interfaces that encourage energy-saving behaviours (e.g., dark mode, sleep prompts).