peterbamuhigire/ux-psychology

UX Psychology — Cognitive Science Foundations

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Use When

• Foundational cognitive science for design. Covers dual-process thinking, memory limits, attention, Gestalt, motivation (SDT), cognitive biases, dark patterns, and design laws (Fitts, Hick-Hyman, Von Restorff). Referenced by all design skills...
• The task needs reusable judgment, domain constraints, or a proven workflow rather than ad hoc advice.

Do Not Use When

• The task is unrelated to ux-psychology or would be better handled by a more specific companion skill.
• The request only needs a trivial answer and none of this skill's constraints or references materially help.

Required Inputs

• Gather relevant project context, constraints, and the concrete problem to solve.
• Confirm the desired deliverable: design, code, review, migration plan, audit, or documentation.

Workflow

• Read this SKILL.md first, then load only the referenced deep-dive files that are necessary for the task.
• Apply the ordered guidance, checklists, and decision rules in this skill instead of cherry-picking isolated snippets.
• Produce the deliverable with assumptions, risks, and follow-up work made explicit when they matter.

Quality Standards

• Keep outputs execution-oriented, concise, and aligned with the repository's baseline engineering standards.
• Preserve compatibility with existing project conventions unless the skill explicitly requires a stronger standard.
• Prefer deterministic, reviewable steps over vague advice or tool-specific magic.

Anti-Patterns

• Treating examples as copy-paste truth without checking fit, constraints, or failure modes.
• Loading every reference file by default instead of using progressive disclosure.

Outputs

• A concrete result that fits the task: implementation guidance, review findings, architecture decisions, templates, or generated artifacts.
• Clear assumptions, tradeoffs, or unresolved gaps when the task cannot be completed from available context alone.
• References used, companion skills, or follow-up actions when they materially improve execution.

References

• Use the links and companion skills already referenced in this file when deeper context is needed.

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Grounded in Hodent (2022), Panzarella (2022), Paduraru (2024), and Klein (2013).

When to Use

Load alongside any design skill when:

• Making layout, navigation, or interaction decisions
• Writing error messages, labels, or instructional copy
• Designing onboarding, motivation, or engagement systems
• Evaluating whether a design respects how users actually think

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1. Dual-Process Model (System 1 / System 2)

System 1 — Fast, automatic, effortless. Handles routine actions, conditioned responses, pattern recognition. Deeply biased but very efficient.

System 2 — Slow, deliberate, resource-intensive. Handles complex reasoning. Does not naturally override System 1.

Design rule: Most users interact via System 1. They are not reading every element — they are scanning, pattern-matching, and satisficing. Design for low-effort, intuitive interaction. Reserve System 2 demands only for genuinely complex decisions.

Satisficing: Users stop reading at the point they believe they have enough information. Put critical content first — never at the end of labels or instructions.

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2. Memory

Three components — all matter for design:

Sensory memory — holds input for under 1 second. If not attended to, it is lost.

Working memory — extremely limited capacity (~3–4 chunks), easily disrupted, requires attentional resources. This is where encoding happens. Every time a user switches context, they lose what was held here.

Long-term memory:

• Explicit — consciously retrievable facts/episodes; fallible; every retrieval is a reconstruction
• Procedural/muscle memory — deeply encoded habits and patterns; very durable; violated conventions force users back to System 2

Miller's Law — Working memory holds ~7 (±2) items; in practice, 3–5 is a safer design target.

• Group interface elements into ≤7 chunks per region; aim for ≤5
• Apply chunking: break phone numbers, IBANs, and codes into groups (555-867-5309, not 5558675309)

Serial Position Effect — Users best remember the first (primacy) and last (recency) items in a list. Middle items are least memorable.

• Place the most important navigation or menu items first or last — never in the middle
• Order destructive or rarely used actions last

Zeigarnik Effect — Incomplete tasks are remembered better than completed ones; open loops create cognitive pull.

• Progress bars, step indicators, and "Your profile is 60% complete" prompts leverage this — open loops draw users back

Design rules:

• Never rely on users remembering instructions from a previous screen
• Never rely on your own memory — document everything
• Respect established conventions (back button, Ctrl+S, swipe-to-delete) — breaking them is always costly
• Recognition beats recall: show options, recent items, and suggestions rather than requiring typed recall

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3. Attention

Attention is scarce, finite, and easily depleted. It works as a filter: focusing on one thing means filtering everything else.

Change blindness — large changes can go completely unnoticed if the user's attention is elsewhere. Animate or highlight changes to ensure they are seen.

Multitasking — largely a myth for cognitive tasks. Tasks sharing attentional demand compete; users degrade in both.

Three types of cognitive load: | Type | What it is | Strategy | |------|-----------|----------| | Intrinsic | Task's inherent complexity | Scaffold with wizards, step indicators, progressive disclosure | | Extraneous | Complexity from poor design | Remove, simplify, group, hide | | Germane | Effort to build mental models | Reinforce with consistent patterns, meaningful defaults |

Selective Attention — Users filter out information irrelevant to their current goal. Anything outside their task path is effectively invisible.

• Never rely on users noticing elements placed outside their active task flow
• Test where users actually look, not where you placed things

Paradox of the Active User — Users never read manuals; they start using the product immediately and muddle through without reading instructions.

• Embed onboarding in the product flow; documentation that requires reading first will be ignored
• Design for learning-by-doing, not reading-before-doing

Design rules:

• Reduce extraneous cognitive load ruthlessly
• New users face maximum intrinsic load — onboard progressively
• Visual hierarchy and contrast direct attention — use them deliberately

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4. Perception & Gestalt

Perception is a subjective construction — not a faithful recording. Context, culture, and expectations all shape what users perceive.

Key Gestalt principles:

• Proximity — elements close together are perceived as grouped
• Similarity — elements sharing attributes (colour, shape, size) are grouped
• Common Region — elements inside a shared boundary (card, panel, divider) are grouped, even without other visual similarity
• Uniform Connectedness — elements connected by a visible line are perceived as more strongly related than proximity alone
• Prägnanz (Law of Good Form) — users perceive the simplest, most stable interpretation of any ambiguous visual; favour clean, unambiguous shapes
• Figure-Ground — primary content must stand out from background; use whitespace deliberately
• Continuity — aligned elements guide the eye along a path
• Closure — users complete incomplete shapes mentally

Mental Model — Users approach your product with expectations built from prior experience with other apps, physical analogies, and conventions.

• Align with users' existing mental models; violation requires explicit explanation
• Jakob's Law: users spend most of their time on other products — they expect yours to work the same way

F-Pattern and Z-Pattern:

• F-Pattern: text-heavy pages; users read top, then scan down the left side
• Z-Pattern: sparse pages; top-left → top-right → diagonal down → bottom-right
• Place key information and CTAs along these natural scan paths

Design rules:

• Never rely on colour alone to communicate meaning (4–10% of users have colour vision deficiency)
• Icons and metaphors are culture-dependent — test across demographics
• Use contrast (size, weight, colour, space) to establish clear reading order

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5. Motivation (Self-Determination Theory)

SDT — the most robust framework for intrinsic motivation. Three needs must be satisfied:

1. Competence — a growing sense of skill and control; feeling increasingly capable
2. Autonomy — meaningful choices; self-expression; not forced into rigid paths
3. Relatedness — social connection; actions that connect to others or shared purpose

Why this matters: Products that satisfy these three needs generate intrinsic engagement. Products that only offer extrinsic rewards (badges, points, streaks) produce fragile engagement that collapses when rewards stop.

Emotion and cognition are inseparable. Emotional design operates at three levels (Norman):

1. Visceral — immediate, automatic response to appearance
2. Behavioral — functional performance; does it work well?
3. Reflective — intellectual response; what values does using this product project?

All three levels are always active. Neglect any one of them and the experience is incomplete.

Design rule: Gamification (badges, points) only addresses extrinsic motivation. For genuine engagement, target competence, autonomy, and relatedness.

Flow (Csikszentmihalyi) — Deep engagement emerges when challenge exactly matches skill level. Too easy = boredom; too hard = anxiety.

• Match task difficulty to the user's current skill level; scaffold progressively as competence grows
• Immediate, unambiguous feedback is a prerequisite for flow — latency or ambiguity breaks the state

Peak-End Rule (Kahneman) — Users judge an experience primarily by its most intense moment (peak) and its ending — not duration or average quality.

• Design exceptional moments at key milestones (first success, first real value delivered)
• Ensure ending states (confirmation screens, completion flows) are delightful — not perfunctory
• Mitigate pain peaks (errors, long loading, failed submissions) as a priority over general polish

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6. Cognitive Biases Every Designer Must Know

| Bias | What it is | Design implication | |------|-----------|-------------------| | Curse of knowledge | You cannot unsee what you know; obvious to you, invisible to users | Always test with people who have never seen your product | | Egocentric bias | You assume others experience the world as you do | You are never your user — research is non-optional | | IKEA effect | You overvalue things you helped build | You are a poor judge of your own product's quality | | Hindsight bias | Everything seems obvious after you know the outcome | Bad decisions looked fine at the time — document your reasoning | | Confirmation bias | You seek data that confirms what you already believe | Actively look for disconfirming evidence in research | | Status quo bias | Users prefer inaction and existing defaults | Design defaults thoughtfully — they determine most outcomes | | Loss aversion | Losing hurts more than equivalent gaining pleases | Sunk-cost thinking is predictable; don't exploit it at users' expense | | Goal-gradient effect | Motivation increases as users approach a goal | Show progress indicators; make users feel they are nearly done | | Scarcity effect | Items perceived as scarce are valued more; abundance decreases perceived value | "Only 3 left", limited availability, early-access — scarcity signals desirability | | Framing effect | Context and presentation change perceived value independently of objective quality | Premium pricing, professional context, and quality signals literally change the experienced pleasure | | Anchoring effect | The first piece of information seen sets a reference point; all subsequent judgements are relative to it | Show full price before discount; sequence options from expensive to cheap; first number anchors the comparison | | Endowed Progress Effect | People are more motivated to complete a goal if they feel they have already made progress toward it | Give new users a head-start on profiles, progress bars, or completion meters — 82% higher completion vs. starting at 0 | | Social Proof & Authority | People look to the behavior of others (especially similar others and authority figures) to guide their own decisions, particularly under uncertainty | User counts, expert endorsements, testimonials, and peer behavior signals reduce decision anxiety. Research base: Bandura's Social Learning Theory — people adopt behaviors they observe in relevant role models. Most effective when targeting users similar to the viewer, not just celebrities. |

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7. Dark Patterns & Ethical Design

Dark patterns (Brignull): design that intentionally deceives users to extract value at their expense.

Common dark patterns:

• Pre-checked subscriptions
• Confirm-shaming ("No thanks, I don't want to save money")
• Hidden costs revealed at payment
• Obscured cancellation flows
• Making the desired action harder to find than the profitable one

Grey-area patterns — not technically deceptive but exploit biases for business gain at user expense:

• Loss aversion exploitation (expiring streaks, "you'll lose your progress")
• Fabricated scarcity ("only 1 left!")
• Opt-out defaults for data sharing, subscriptions, auto-renewal
• Auto-play without explicit consent
• Push notifications without genuine value

How to distinguish nudge from dark pattern: A nudge changes behaviour for the long-term benefit of the user or society (seat belt reminder, exercise prompt). A dark pattern changes behaviour for business benefit at the user's expense. The test is: whose interests are served?

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8. Design Laws

Fitts's Law

Time to point at a target increases as target size decreases and distance increases.

• Make primary action buttons large and close to common starting positions
• Make destructive/accidental-click-risk buttons smaller and further away
• Minimum touch target: 44×44px (web), 48dp (Android)

Hick-Hyman Law

Decision time increases logarithmically with the number of options.

• Present ≤7 options per group (aim for ≤5)
• Use categories and filtering to reduce apparent choice count
• Provide smart defaults to eliminate unnecessary decisions
• Indecision ("analysis paralysis") causes users to disengage entirely

Von Restorff Effect

The more an element stands out, the better it is noticed and remembered.

• Use contrast, size, colour, and motion deliberately
• When too many elements compete for attention, nothing stands out

Pareto Principle (80/20)

80% of user activity involves only 20% of features.

• Identify the core 20% and make them prominent
• Don't clutter the interface with rarely used features

Jakob's Law

Users spend most of their time on other products. They expect yours to work the same way.

• Follow established conventions for navigation, search, forms, and interactions
• Innovation has a learning cost — deviate from convention only when the benefit clearly outweighs it

Aesthetic-Usability Effect

Aesthetically pleasing designs are perceived as easier to use, even when they aren't.

• Polish UI — users tolerate minor usability problems in beautiful interfaces
• This effect fades with repeated exposure; function must ultimately deliver

Doherty Threshold

When system response time drops below 400ms, users stay engaged; above 400ms attention breaks.

• Target <100ms for perceived-instant feedback; <400ms for any interactive action
• Use skeleton screens, optimistic UI, and progress indicators when performance cannot be guaranteed

Tesler's Law (Law of Conservation of Complexity)

Every system has inherent complexity that cannot be eliminated — only moved.

• Simplifying the UI shifts complexity to the backend or documentation
• Decide consciously who bears the complexity: the product or the user

Occam's Razor

Among competing designs, prefer the simplest one that adequately solves the problem.

• Remove every element that does not serve a clear purpose; when in doubt, leave it out

Parkinson's Law

Work expands to fill the time available — and users fill whatever input space they are given.

• Set time constraints on tasks to create urgency; don't provide more input space than needed

Postel's Law (Robustness Principle)

Be conservative in what you send; be liberal in what you accept.

• Accept varied input formats (phone with/without dashes, dates in multiple formats)
• Validate with helpful correction, not rejection: "We'll format that" not "Invalid input"
• Return consistent, clean, predictable output regardless of input variation

Choice Overload

Too many options reduces satisfaction and increases the likelihood of no decision at all.

• Cap primary choices at ≤5; use categories and filtering for large option sets
• Provide a recommended default — most users will take it; it eliminates unnecessary decisions

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9. Key Mantras

1. "You are not your users." — the cardinal rule of UX
2. "We don't design an experience; we design for an experience." — Hodent. Experiences happen in the user's mind.
3. "Design for System 1." — Most interactions happen automatically; remove the need for deliberate effort
4. "Recognition over recall." — Show options; don't make users remember
5. "Satisficing is always happening." — Users stop reading when they think they have enough. Put critical content first.
6. "People don't want a drill; they want to install bookshelves." — Norman. Design for outcomes, not features.
7. "Convention violation is always costly." — Breaking established patterns forces users into System 2.
8. "Defaults are decisions." — Most users never change defaults; design them thoughtfully.

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10. Tidwell's Behavioral Design Patterns (Cross-Reference)

The interaction-design-patterns skill provides Tidwell's 12 behavioral patterns that complement the cognitive science above. Each Tidwell pattern has a direct cognitive foundation:

| Tidwell Pattern | Cognitive Foundation | |----------------|---------------------| | Satisficing | System 1 + working memory limits — users satisfice because parsing is work | | Habituation | Procedural memory — habituated gestures bypass conscious thought | | Spatial Memory | Procedural + explicit memory — location is encoded as part of the learned pattern | | Deferred Choices | Cognitive load — unnecessary decisions increase extraneous load | | Instant Gratification | Motivation (SDT) — early competence feelings drive continued engagement | | Safe Exploration | Anxiety reduction (Emotion Mind) — fear of mistakes suppresses exploration | | Incremental Construction | Flow state (Csikszentmihalyi) — immediate feedback is prerequisite for flow | | Streamlined Repetition | Habituation + efficiency — reduce System 2 demand on routine tasks | | Prospective Memory | Prospective memory theory — externalising reminders offloads working memory | | Social Proof | Loss aversion + relatedness (SDT) — peer behaviour reduces decision uncertainty |

Load interaction-design-patterns alongside this skill for the full pattern library.

Load habit-forming-products when designing for repeat, unprompted engagement. That skill operationalises the IKEA effect, goal-gradient, scarcity, framing, anchoring, and endowed progress into the Hook Model (Trigger → Action → Variable Reward → Investment).

Load laws-of-ux when you need to cite or look up any named UX law by name. That skill is the complete named-law quick-reference for all 30 Yablonski Laws of UX with design rules, grouped by law family.

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Sources

• Hodent, C. (2022). What UX Is Really About. CRC Press.
• Panzarella, L. (2022). UI/UX Web Design Simply Explained.
• Paduraru, E. (2024). Roots of UI/UX Design. Creative Tim.
• Norman, D. (2013). The Design of Everyday Things. Basic Books.
• Kahneman, D. (2011). Thinking, Fast and Slow. Farrar, Straus and Giroux.
• Tidwell, J., Brewer, C., Valencia, A. (2020). Designing Interfaces, 3rd ed. O'Reilly.
• Eyal, N. & Hoover, R. (2014). Hooked: How to Build Habit-Forming Products. Portfolio/Penguin. (Scarcity, Framing, Anchoring, Endowed Progress, Social Proof effects)
• Bandura, A. (1977). Social Learning Theory. Prentice Hall. (Social Proof / observational learning)
• Yablonski, J. (2024). Laws of UX, 2nd ed. O'Reilly. (lawsofux.com — all named laws)
• Csikszentmihalyi, M. (1990). Flow: The Psychology of Optimal Experience. Harper & Row.
• Miller, G. A. (1956). "The Magical Number Seven, Plus or Minus Two." Psychological Review.