1.0 Introduction & Definition of HCI
Human-Computer Interaction (HCI) is the study, design, and evaluation of how people interact with computational systems. It is an interdisciplinary field focused on creating usable, efficient, and satisfying interfaces.
-
Scope: Encompasses the design, implementation, and assessment of interactive computing systems for human use.
-
Interdisciplinary Nature: Integrates knowledge from:
-
Computer Science (algorithms, systems)
-
Cognitive & Social Psychology (human behavior)
-
Design (visual, interaction, industrial)
-
Human Factors/Ergonomics (physical aspects)
-
The Human as an Information Processor:
A simplified model where the human:
-
Inputs information via sensory organs (eyes, ears, hands).
-
Processes information in cognitive systems (perception, memory, reasoning).
-
Outputs actions via motor systems (keyboard, mouse, voice).
[!TIP] Computer: Tool vs. Partner
- Tool: Passive, requires user to initiate all actions (e.g., command line).
- Partner: More active, can anticipate, suggest, or collaborate (e.g., AI assistants, predictive text).
Importance of Good HCI:
| Benefit Type | Key Points |
|---|---|
| Economic | ↑ Productivity, ↓ Errors & training costs, ↓ Support costs, Competitive advantage. |
| Social | ↑ Accessibility for diverse abilities, ↑ Quality of life (e.g., assistive tech), Digital inclusion. |
| Ethical | Responsibility to design for all potential users (inclusivity), Avoid bias, Ensure privacy. |
2.0 A Brief History of HCI
| Era | Time Period | Key Characteristics & Technologies | Pioneers & Milestones |
|---|---|---|---|
| Early Era | 1940s-1960s | Batch processing, No direct user interaction, Punched cards/paper tape. | ENIAC, UNIVAC – computers as room-sized calculators. |
| Birth of Interactive Computing | 1960s-1970s | Mouse invented, Graphical displays, Direct manipulation concepts. | Douglas Engelbart (Mother of All Demos, 1968), Ivan Sutherland (Sketchpad, 1963). |
| Personal Computer Revolution | 1980s | WIMP Paradigm dominant (Windows, Icons, Menus, Pointer). | Apple Macintosh (1984), Microsoft Windows (1985). Shift to personal productivity. |
| Web & Ubiquitous Computing | 1990s-2000s | World Wide Web (browsers), Mobile devices, Ubicomp vision. | Tim Berners-Lee (WWW, 1989/1991), Mark Weiser (Ubiquitous Computing, 1991). |
| Current Era | 2010s-Present | Touch, Gesture, Voice interfaces, AR/VR, IoT, AI-driven adaptive UIs. | Smartphones, Amazon Alexa, Oculus Rift, Context-aware systems. |
[!TIP] Exam Focus: Be able to link eras → key interface paradigms → key figures. The shift from batch → interactive → WIMP → post-WIMP (touch/voice) is a critical narrative.
3.0 Core Concepts: Usability and User Experience (UX)
3.1 Defining Usability (ISO 9241-11)
"The extent to which a system can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use."
| Attribute | Definition | Measurement Focus |
|---|---|---|
| Learnability | How easy is it for new users to accomplish basic tasks? | Time to reach a proficiency level. |
| Memorability | How easily can users re-establish proficiency after a break? | Time to perform task after period of non-use. |
| Efficiency | How quickly can experienced users perform tasks? | Time/actions per task after learning. |
| Errors | How many errors do users make? How severe are they? Can they recover easily? | Error rate, error severity, recoverability. |
| Satisfaction | How pleasant is the system to use? | Subjective questionnaires (e.g., SUS). |
3.2 Defining User Experience (UX)
A broader, holistic concept encompassing all aspects of the end-user's interaction with a company, its services, and its products.
Components (Peter Morville's Honeycomb): Useful, Usable, Desirable, Findable, Accessible, Credible, Valuable.
3.3 Relationship: Usability vs. UX
-
Usability is a subset of UX. It focuses on task completion (effectiveness, efficiency).
-
UX encompasses usability plus emotional, aesthetic, and experiential factors (e.g., joy, trust, brand perception).
-
Analogy: A system can be usable (you can check out) but have poor UX (the process is frustrating or ugly).
3.4 The Cost of Poor Usability
| Cost Type | Examples |
|---|---|
| Direct | ↑ Customer support calls, ↑ Training time/costs, ↑ Development rework, ↑ Documentation needs. |
| Indirect | ↓ User productivity, Customer frustration & churn, Brand damage, Lost sales, Safety risks. |
[!TIP] Common Pitfall: Confusing "usable" with "useful." A system can be perfectly usable but completely useless for the user's real goals. Usefulness (does it do what I need?) is a prerequisite for good UX.
4.0 The HCI Design Process
4.1 The Four Basic Activities (Iterative Cycle)
-
Need Identification & Requirements Gathering: Understand the problem, users, tasks, and context. (Output: Requirements Specification).
-
Design: Generate solutions. Create prototypes (sketches, wireframes, interactive mockups) at varying fidelity.
-
Implementation: Build the functional system based on the design.
-
Evaluation: Assess the design/implementation with real users or experts. (Output: Findings → feed back to design).
4.2 Iteration: The Core Principle
"Design → Evaluate → Redesign" is repeated. Early, low-cost prototypes (paper, digital wireframes) are tested to find major flaws before expensive coding begins.
4.3 Development Lifecycle Models in HCI
| Model | Approach | Suitability for HCI | Key Limitation |
|---|---|---|---|
| Waterfall | Linear, sequential phases (Req → Design → Code → Test). | Poor fit. User needs often unclear upfront; late testing is costly. | Inflexible, assumes stable requirements. |
| Iterative / Agile | Cyclical, incremental development with continuous user feedback. | Ideal fit. Embraces changing requirements, early & frequent user testing. | Requires user availability, can lead to scope creep if not managed. |
[!TIP] Exam Key: Always advocate for iterative/user-centered design in HCI. The waterfall model is a classic example of what not to do for interactive systems.
5.0 Understanding Users
5.1 User Characteristics
| Category | Factors |
|---|---|
| Physical | Age, Motor skills (dexterity, strength), Sensory abilities (vision, hearing). |
| Cognitive | Memory capacity, Attention span, Perception speed, Mental models (user's understanding of how the system works). |
| Personality & Experience | Tech-savviness, Risk tolerance, Patience, Prior experience with similar systems. |
5.2 User Diversity and Inclusivity
-
Designing for Disabilities: Follows accessible/universal design principles. Goal: one design for widest audience.
-
Visual: Screen readers (alt text), high contrast, scalable text.
-
Auditory: Captions for audio, visual alerts.
-
Motor: Keyboard navigation, large click targets, voice control.
-
Cognitive: Simple language, consistent layout, error prevention.
-
-
Cultural Differences: Color meanings (white = purity vs. mourning), reading direction (LTR vs. RTL), icon metaphors, privacy norms.
5.3 User Context
-
Physical Environment: Lighting (glare), Noise (auditory interfaces), Space (mobile vs. desktop), Mobility.
-
Social Context: Is the user alone or collaborating? Privacy needs? Social acceptability of the device/input method.
-
Task Context: Frequency (daily vs. occasional), Criticality (life-threatening vs. casual), Goal structure (single-step vs. complex workflow).
[!TIP] Golden Rule: "Know thy user." All design decisions must be justified by user characteristics and context, not technical convenience.
6.0 Fundamental Interdisciplinary Influences
6.1 Cognitive Psychology
-
Mental Models: The user's internal representation of how a system works. Good design aligns the system image (what the interface shows) with a correct mental model.
-
Cognitive Load Theory: Design should minimize extraneous cognitive load (unnecessary mental effort) to free resources for germane load (understanding the task).
-
Attention & Perception (Gestalt Principles): How users group visual elements.
- Proximity, Similarity, Continuity, Closure, Figure/Ground.
-
Memory: Recognition vs. Recall: Recognition (seeing an option) is easier than Recall (remembering a command). Favor menus over command lines.
6.2 Sociology & Anthropology
-
Social Computing: How systems support social interaction (social media, collaboration tools).
-
Ethnography & Field Studies: Observing users in their natural context to understand real workflows and unarticulated needs. Essential for contextual inquiry.
6.3 Computer Science & Engineering
-
Algorithms & Data Structures: Impact system performance (response time), which directly affects usability (e.g., <100ms feels instantaneous).
-
Input/Output Technologies: Constraints and affordances of different devices (touch vs. mouse vs. keyboard).
-
Software Engineering: Modularity, APIs, and system architecture affect what is feasible to implement and test.
6.4 Design & Human Factors
-
Visual Design Principles: Layout (grids, alignment), Color (contrast, meaning), Typography (readability, hierarchy).
-
Industrial Design: Physical form factor of devices (shape, weight, button placement).
-
Ergonomics: Physical comfort and safety (e.g., keyboard angle, monitor height to prevent RSI).
[!TIP] Interdisciplinary Synthesis: Great HCI happens at the intersection. Example: A cognitive psychologist knows recognition is easier than recall, a designer creates a clear menu, and a software engineer ensures it loads in <100ms. All three perspectives are essential.