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Human-Centered Design Fundamentals

Design products that accommodate actual human cognition and behavior rather than expecting humans to adapt to arbitrary system requirements.

When to Use

✅ Use for:

• Physical product design (doors, appliances, controls, tools)
• Digital interface design (software, touchscreens, dashboards)
• System design where human error is critical (medical devices, industrial controls, aircraft)
• Redesigning systems after repeated user errors
• Creating instructions and documentation
• Error prevention and safety-critical systems

❌ NOT for:

• Pure visual design without functional components
• Marketing and brand identity
• Autonomous systems with no human interaction
• Systems where users have unlimited training time and perfect memory

Core Process

Seven Stages of Action Decision Tree

START: User encounters system
│
├─→ Is this GOAL-DRIVEN (user has objective)?
│   ├─→ YES: Begin at Stage 1 (Form Goal)
│   │   ├─→ Can user identify what they want? 
│   │   │   ├─→ NO: MISTAKE likely → Provide clear conceptual model
│   │   │   └─→ YES: Proceed to Stage 2
│   │   │
│   │   ├─→ Stage 2: Plan action sequence
│   │   │   ├─→ Are alternatives clear?
│   │   │   │   ├─→ NO: MISTAKE likely → Improve discoverability
│   │   │   │   └─→ YES: Proceed to Stage 3
│   │   │
│   │   ├─→ Stage 3: Specify action
│   │   │   ├─→ Is correct action obvious?
│   │   │   │   ├─→ NO: Gulf of Execution too wide → Add signifiers
│   │   │   │   └─→ YES: Proceed to Stage 4
│   │   │
│   │   └─→ Stage 4: Perform action
│   │       ├─→ Is user expert (subconscious execution)?
│   │       │   ├─→ YES: High SLIP risk → Add forcing functions
│   │       │   └─→ NO: Conscious execution → Provide clear affordances
│   │
└─→ Is this EVENT-DRIVEN (environmental trigger)?
    └─→ YES: Begin at Stage 5 (Perceive state)
        ├─→ Stage 5: Perceive world state
        │   ├─→ Is feedback immediate (<0.1s)?
        │   │   ├─→ NO: Add immediate feedback
        │   │   └─→ YES: Proceed to Stage 6
        │
        ├─→ Stage 6: Interpret perception
        │   ├─→ Does system state make sense?
        │   │   ├─→ NO: Gulf of Evaluation too wide → Improve conceptual model
        │   │   └─→ YES: Proceed to Stage 7
        │
        └─→ Stage 7: Compare with goal
            ├─→ Is outcome clear?
            │   ├─→ NO: Add better feedback + conceptual model
            │   └─→ YES: Action cycle complete
            │
            └─→ Goal achieved?
                ├─→ NO: Return to Stage 2 (new plan)
                └─→ YES: END

Design Evaluation Decision Tree

EVALUATE DESIGN: Start here
│
├─→ Discoverability Check
│   ├─→ Can user determine possible actions without instructions?
│   │   ├─→ NO: Missing signifiers → Add visible indicators
│   │   └─→ YES: Check constraints
│   │
│   ├─→ Are constraints visible and effective?
│   │   ├─→ NO: Add physical/semantic/cultural/logical constraints
│   │   └─→ YES: Check mapping
│   │
│   └─→ Is control-to-effect mapping natural?
│       ├─→ NO: Redesign spatial relationships or use cultural conventions
│       └─→ YES: Proceed to Understanding Check
│
├─→ Understanding Check
│   ├─→ Does system image communicate conceptual model?
│   │   ├─→ NO: Improve structure, labels, documentation
│   │   └─→ YES: Check feedback
│   │
│   ├─→ Is feedback immediate and informative?
│   │   ├─→ NO: Add/improve feedback mechanisms
│   │   └─→ YES: Check processing levels
│   │
│   └─→ Are all three levels addressed?
│       ├─→ Visceral: Is it aesthetically appealing?
│       ├─→ Behavioral: Does it support learned patterns?
│       └─→ Reflective: Will memory of use be positive?
│
└─→ Error Prevention Check
    ├─→ What error types are possible?
    │   ├─→ SLIPS (execution errors)?
    │   │   └─→ Add forcing functions, reduce steps, prevent capture
    │   ├─→ MISTAKES (planning errors)?
    │   │   └─→ Improve conceptual model, add feedforward
    │   └─→ MEMORY LAPSES?
    │       └─→ Put knowledge in world, add reminders, minimize steps
    │
    ├─→ Are modes present?
    │   ├─→ YES: MODE ERROR risk
    │   │   ├─→ Can you eliminate modes?
    │   │   │   ├─→ YES: Eliminate them
    │   │   │   └─→ NO: Make current mode extremely salient
    │   │
    └─→ Does security exceed human capability?
        └─→ YES: Users will create workarounds → Redesign for actual capabilities

Root Cause Analysis Process

INCIDENT OCCURS
│
├─→ Ask: "What happened?" (Identify symptom)
│   └─→ Document observable failure
│
├─→ Ask: "Why did this happen?" (First cause)
│   ├─→ Answer: "Human error"
│   │   └─→ NEVER STOP HERE - This is anti-pattern
│   └─→ Continue investigation
│
├─→ Ask: "Why did the human make that error?" (Second why)
│   ├─→ Was signifier missing/unclear?
│   ├─→ Was feedback absent/poor?
│   ├─→ Was mapping unnatural?
│   ├─→ Was conceptual model wrong?
│   └─→ Continue for each factor
│
├─→ Ask: "Why was design inadequate?" (Third why)
│   └─→ Investigate design process failures
│
├─→ Ask: "Why did process fail?" (Fourth why)
│   └─→ Investigate organizational factors
│
├─→ Ask: "Why did organization allow this?" (Fifth why)
│   └─→ Reach fundamental systemic cause
│
└─→ DECISION: Fix person or fix system?
    ├─→ Multiple people made same error?
    │   └─→ YES: System design failure → REDESIGN SYSTEM
    └─→ Isolated incident with unique circumstances?
        └─→ Investigate further - may still be system issue

Anti-Patterns

🚫 Blaming Human Error

Novice approach:

• Incident occurs
• Investigation identifies operator action as proximate cause
• Conclusion: "Human error - operator needs retraining"
• Action: Discipline/replace operator, add more warnings
• Timeline: Immediate blame assignment within hours/days

Expert approach:

• Incident occurs
• Acknowledge human action as symptom, not cause
• Apply Five Whys: "Why did operator make that choice?"
• Discover: Ambiguous signifier, mode confusion, inadequate feedback, excessive memory load
• Conclusion: "System failed to support human capabilities"
• Action: Redesign interface to prevent error conditions
• Timeline: Weeks of investigation to understand systemic factors

Shibboleth: "If an error is common, it's a design failure. Human error usually is a result of poor design: it should be called system error."

🚫 Norman Doors (Signifier Failure)

Novice approach:

• Design beautiful door with minimal visual interruption
• Use identical hardware on both sides
• Add small "PUSH" sign when people struggle
• Blame users for not reading sign
• Timeline: Sign added after first complaints (days)

Expert approach:

• Design inherently communicates operation
• Push side: Flat plate (anti-affordance for pulling)
• Pull side: Vertical handle (affordance for gripping)
• Hinge side visible where applicable
• No signs needed - hardware IS the signifier
• Timeline: Correct from initial design specification

Shibboleth: "The design of the door should indicate how to work it without any need for signs, certainly without any need for trial and error."

🚫 Mode Errors

Novice approach:

• Single button performs different functions in different modes
• Mode indicated by small icon or buried in menu
• User manual explains mode system
• "Users should remember current mode"
• Timeline: Mode confusion appears immediately but attributed to user error

Expert approach:

• Minimize modes entirely - use different controls for different functions
• If modes unavoidable: Make current mode EXTREMELY salient
• Use forcing functions to prevent dangerous mode transitions
• Physical mode indicators that cannot be overlooked
• Test with interruptions to verify mode clarity
• Timeline: Mode clarity validated during prototype testing before release

Shibboleth: "Mode errors are design errors. When equipment has multiple modes, the equipment must make the mode clearly visible."

🚫 Knowledge-In-Head Assumption

Novice approach:

• Expect users to memorize 8+ character passwords with mixed case, numbers, symbols
• Require remembering multi-step procedures
• Provide training once, assume retention
• "Users need to pay more attention"
• Timeline: Password policies created in single meeting

Expert approach:

• Recognize working memory holds 3-7 items, fragile under interruption
• Design puts knowledge in world: Structure, constraints, visible reminders
• Multi-factor authentication: "Something you have" + "something you know"
• Procedures self-evident from interface structure
• Checklists and external aids for critical sequences
• Timeline: Iterative testing reveals memory failures; design evolves

Shibboleth: "The most effective way of helping people remember is to make it unnecessary. Put required knowledge in the world."

🚫 Missing Feedback

Novice approach:

• Button press triggers background process
• No indication action was received
• User unsure if click registered
• User clicks multiple times ("button mashing")
• System processes multiple requests
• Timeline: Complaint emerges after users discover duplicates (days/weeks)

Expert approach:

• Immediate feedback within 0.1 seconds of action
• Button shows depressed state
• Progress indicator for operations >1 second
• Clear completion confirmation
• Prevent duplicate actions through lock-in forcing function
• Timeline: Feedback designed into initial prototype

Shibboleth: "Feedback must be immediate, informative, and appropriately prioritized. Poor feedback can be worse than no feedback."

🚫 Aesthetics Over Usability

Novice approach:

• Hide all controls for visual minimalism
• Invisible door hardware (smooth glass)
• Touch-sensitive surfaces with no tactile feedback
• "Clean design" means featureless
• Timeline: Awards received; usability complaints ignored for years

Expert approach:

• Beauty and usability need not conflict
• Controls visible but elegantly integrated
• Signifiers enhance rather than detract from aesthetics
• Address visceral (beauty) AND behavioral (usability) AND reflective (pride of ownership)
• Timeline: Iterative prototypes balance all three processing levels

Shibboleth: "Attractive things work better - but only when they ALSO work well. Good design is invisible because it fits needs perfectly."

🚫 Excessive Security Theater

Novice approach:

• 12+ character passwords changed monthly
• Complex rules: uppercase, lowercase, numbers, symbols, no dictionary words
• Multiple authentication steps for routine tasks
• Lock users out after 3 failed attempts
• Timeline: Security policy implemented top-down in single quarter

Expert approach:

• Recognize humans cannot remember 50+ complex passwords
• Accept reality: Excessive security → insecurity via workarounds
• Users write passwords on monitors, use "Password123!", disable locks
• Design FOR human limitations: Password managers, biometrics, tokens
• Balance security with usability to prevent counterproductive behavior
• Timeline: Security usability testing reveals actual user behavior; policy adjusted

Shibboleth: "Making systems too secure makes them less secure. We must accept human behavior the way it is, not the way we wish it to be."

Mental Models & Shibboleths

Gulf Metaphor:

• Novice: "Users need training to cross the gulf"
• Expert: "Designer builds bridges across gulfs through signifiers (execution) and feedback + conceptual models (evaluation)"

Knowledge Distribution:

• Novice: "Users should memorize procedures"
• Expert: "Combination of person + artifact creates intelligence; design puts knowledge in world"

Error Attribution:

• Novice: "Operator error caused failure"
• Expert: "Never stop at human error - apply Five Whys to reach systemic cause"

Swiss Cheese Model:

• Novice: "Find the single root cause"
• Expert: "Accidents occur when holes in multiple defensive layers align simultaneously"

Action Cycles:

• Novice: "Users always start with clear goals"
• Expert: "Behavior can be goal-driven (top-down) or event-driven (opportunistic) - design supports both"

Processing Levels:

• Novice: "Focus on functionality"
• Expert: "Address visceral (immediate aesthetics), behavioral (learned patterns), and reflective (long-term memory and meaning)"

Temporal Knowledge

1988 (Original Edition): Focus on affordances; academic cognitive psychology perspective; "Psychology of Everyday Things" title emphasized scientific foundation

2013 (Revised Edition): Shifted emphasis from affordances to signifiers after recognizing confusion in digital design community; added chapters on emotion, experience design, and design thinking; incorporated business and industry perspectives from author's Apple/HP experience

Pre-automation era (<1900s): Direct physical manipulation; immediate mechanical feedback; human operators controlled complex systems with transparent cause-effect relationships

Modern automation (1900s-2000s): Separation of users from direct system control; new error modes from automation; "ironies of automation" where increased automation demands higher operator skill

Touchscreen era (2000s+): Loss of physical affordances; gesture-based interaction; metaphor shift from "moving window" to "moving text" scrolling; elimination of tactile feedback requiring stronger visual signifiers

Current challenge (2010s+): Balancing security requirements with human cognitive limitations; designing for interruption-heavy multitasking environments; accommodating aging populations with declining capabilities

References

• Source: "The Design of Everyday Things" (Revised and Expanded Edition, 2013) by Don Norman
• Original Edition: "The Psychology of Everyday Things" (1988)
• Foundation: Cognitive psychology research on human perception, memory, action, and error