Cognitive Foundations
The science of how minds work, and what that means for design.
When to Use This Skill
- Explaining *why* a design works or fails (grounded in research, not opinion)
- Evaluating cognitive load or working memory demands
- Predicting user performance (Fitts, Hick-Hyman)
- Diagnosing mental model misalignment
- Justifying design decisions to stakeholders with evidence
- Understanding attention, perception, or memory failures
Output Contracts
For Single-Principle Analysis
## Cognitive Principle: [Name]
**Principle**: [1-sentence explanation]
**Evidence in Design**: [Where/how this applies]
**Implication**: [Specific, actionable recommendation]
**Confidence**: [High/Medium/Low] — [rationale]For Cognitive Audit (Comprehensive)
## Cognitive Audit: [Screen/Flow Name]
### Working Memory Load
- Items requiring recall: [count]
- Cross-screen memory demands: [Y/N]
- Verdict: [Acceptable / High / Overloaded]
### Attention Demands
- Preattentive features for critical info: [Y/N]
- Competing attention demands: [list]
- Change blindness risk: [areas where changes may go unnoticed]
### Mental Model Alignment
- Expected user model: [what users likely think]
- System behavior: [what actually happens]
- Gap: [mismatch, if any]
### Predictive Laws
- Fitts's Law concerns: [target size/distance issues]
- Hick's Law concerns: [choice overload areas]
### Gulf Analysis
- Gulf of Execution: [unclear how to act?]
- Gulf of Evaluation: [unclear what happened?]
### Violations of Nielsen's Heuristics
| Heuristic | Violation | Severity |
|-----------|-----------|----------|
| ... | ... | 1-4 |
### Recommendations
1. [Highest priority fix]
2. [Second priority]
3. [Third priority]For Explaining a Failure
## Failure Analysis: [What Went Wrong]
**Observed Behavior**: [What users did]
**Cognitive Explanation**: [Which principle explains this]
**Root Cause**: [Design element that caused it]
**Fix**: [Specific change]Quick Reference: Predictive Laws
| Law | Formula | Rule of Thumb |
|---|---|---|
| Fitts's Law | MT = a + b × log₂(2D/W) | Bigger + closer = faster. Screen edges are infinite. |
| Hick-Hyman | RT = a + b × log₂(n+1) | More choices = slower. Reduce or organize options. |
| Steering Law | T = a + b × (A/W) | Narrow paths are slow. Cascading menus are hard. |
| Power Law | T = a × N^(-b) | Practice helps. Design for learnability. |
Quick Reference: Nielsen's 10 Heuristics
| # | Heuristic | Quick Test |
|---|---|---|
| 1 | Visibility of system status | Can user always tell what's happening? |
| 2 | Match system ↔ real world | Language familiar? Metaphors sensible? |
| 3 | User control and freedom | Easy undo? Clear exits? |
| 4 | Consistency and standards | Same words/actions mean same things? |
| 5 | Error prevention | Constraints prevent errors before they occur? |
| 6 | Recognition over recall | Options visible? No memory required? |
| 7 | Flexibility and efficiency | Shortcuts for experts? |
| 8 | Aesthetic and minimalist | Only relevant info? No clutter? |
| 9 | Error recovery | Errors explained in plain language with fix? |
| 10 | Help and documentation | Searchable, task-focused, concise? |
Quick Reference: Working Memory
- Capacity: ~4 chunks (not 7)
- Duration: ~20 seconds without rehearsal
- Test: Count items user must hold in mind across screens/steps
Red flags:
- "Remember this code and enter it on the next page"
- Multi-step forms without visible progress/state
- Complex comparisons requiring mental tracking
Quick Reference: Preattentive Features
Detected in <200ms, no focused attention required:
- Color (hue, saturation)
- Size (length, area)
- Orientation (angle)
- Motion (flicker, direction)
- Shape (curvature, enclosure)
Use for: Critical info, errors, changes, status Don't use for: Everything (loses signal value)
Cognitive Load Checklist
Quick assessment for any interface:
| Factor | Low Load | High Load |
|---|---|---|
| Choices visible | 2-4 options | 10+ options |
| Memory demands | Recognition | Recall |
| Steps to goal | 1-3 clicks | 5+ clicks |
| Interruptions | None | Frequent modals |
| Novel elements | Familiar patterns | New conventions |
| Error recovery | Clear undo | Destructive actions |
| Visual complexity | Clean, grouped | Dense, undifferentiated |
Scoring: Each "High Load" = +1. Score >3 = redesign needed.
Common Violations → Principle
| Symptom | Likely Violation | Fix |
|---|---|---|
| Users don't notice changes | Change blindness | Animate, highlight transitions |
| Users can't find the button | Poor Fitts's Law | Increase size, reduce distance |
| Users freeze at options | Hick's Law overload | Reduce choices, progressive disclosure |
| Users forget mid-task | Working memory exceeded | Show state, don't require recall |
| Users misunderstand state | Gulf of Evaluation | Better feedback, visibility |
| Users click wrong thing | Poor affordance/signifier | Clearer visual treatment |
| Users make same error repeatedly | Mode error | Visible mode indicators |
| Users abandon complex forms | Cognitive load | Chunk, scaffold, save progress |
Process
- Identify cognitive demands — What is the interface asking the user to perceive, remember, decide, or do?
- Match to principles — Which cognitive constraints or laws apply?
- Evaluate alignment — Does the design respect or violate these?
- Recommend changes — Specific modifications grounded in the principle
Deep Reference Files
For comprehensive principles and research:
- PSYCHOLOGY.md — Perception, memory, attention, biases, emotion, motivation
- HCI-THEORY.md — Norman's model, predictive laws, error theory, research methods, heuristics
Primary Sources
- A Feature-Integration Theory of Attention.md — Treisman & Gelade on preattentive processing (informs: Quick Reference: Preattentive Features)
- Judgment under Uncertainty- Heuristics and Biases.md — Kahneman & Tversky on cognitive biases (informs: PSYCHOLOGY.md § Decision Making)
Key Researchers
- Don Norman: Affordances, gulfs, emotional design
- Daniel Kahneman: Dual process theory, heuristics and biases
- Stuart Card: GOMS, information foraging, Fitts's Law
- Anne Treisman: Feature integration, preattentive processing
- Jakob Nielsen: Usability heuristics, discount usability
- Ben Shneiderman: Direct manipulation, golden rules
Remember
- Cognitive science explains *why* design principles work
- Individual differences exist—design for variability, not averages
- Lab findings may not generalize (ecological validity matters)
- Theory informs but doesn't replace observing real users
- When in doubt, reduce cognitive load—users have less capacity than you think