Product Psychology

Product psychology is the applied end of this site: it takes findings about attention, memory,
judgement and motivation and turns them into decisions a design or product team can actually ship —
what to put on a screen, how many options to offer, when to ask for commitment, and what to do about
users whose brains work differently from the "average user" a spec assumes.

This section holds 132 reference pages in three groups:

Group	Size	Use it when
The Psychology of Design	119 pages	You need a named principle or bias to explain, predict or fix behaviour
Neurodiversity Design System	12 pages	You are making an interface work for dyslexic, ADHD, autistic users
AI in Psychology	1 page	You are evaluating AI tools in mental-health and emotional contexts

The Psychology of Design

The 119 principle pages are organised around what the brain is doing when it meets your product.
Users filter most of what you show them, infer meaning from the little that survives, decide
under time pressure, and later remember only fragments. Each stage fails in its own way, so start
from the stage where your product is losing people.

1. Information filtering — 38 pages

Users ignore most of the screen. These pages cover what gets seen and what gets skipped.

Cognitive Load ·
Hick's Law ·
Fitts's Law ·
Visual Hierarchy ·
Progressive Disclosure ·
Banner Blindness ·
Selective Attention ·
Von Restorff Effect ·
Framing ·
Anchoring Bias ·
Decoy Effect ·
Tesler's Law
→ all 38

2. Meaning making — 33 pages

Whatever survives the filter gets a story attached to it, usually the wrong one.

Mental Models ·
Social Proof ·
Scarcity ·
Reciprocity ·
Halo Effect ·
Miller's Law ·
Curiosity Gap ·
Aha! Moment ·
Flow State ·
Variable Reward ·
Law of Prägnanz ·
Curse of Knowledge
→ all 33

3. Time and decisions — 22 pages

Decisions are made in a hurry, with shortcuts. This is where pricing, onboarding and checkout live.

Loss Aversion ·
Sunk Cost Effect ·
Doherty Threshold ·
Decision Fatigue ·
Hyperbolic Discounting ·
Default Bias ·
Labor Illusion ·
Reactance ·
Parkinson's Law ·
Weber's Law ·
Dunning-Kruger Effect ·
Pareto Principle
→ all 22

4. Memory — 26 pages

What users recall about your product later is not what happened. It is a summary, weighted oddly.

Peak-End Rule ·
Serial Position Effect ·
Zeigarnik Effect ·
Chunking ·
Recognition Over Recall ·
IKEA Effect ·
Endowment Effect ·
Spacing Effect ·
Storytelling Effect ·
Picture Superiority Effect ·
Negativity Bias ·
Method of Loci
→ all 26

Neurodiversity Design System

An implementation-level design system for users with learning and processing differences — each page
pairs guidelines with working CSS and React code, so it can be applied directly rather than
interpreted.

Layer	Pages
Who you design for	Neurodiversity Types · Learner Personas
Visual layer	Typography · Colour · Layout
Interaction layer	Interaction · Forms · Navigation
Regulation layer	Attention & Focus · Sensory Processing · Animation & Motion

Applying this without fooling yourself

A named bias explains a result; it does not prove one. Principles from this section are hypotheses
about your users, and most of them can be checked cheaply.

Locate the failure. Which stage is losing people — filtering, meaning, decision or memory?
Pick a principle, state a prediction. "Cutting the plan grid from nine options to three raises
completion" is testable; "reduce cognitive load" is not.
Measure it properly. Effect sizes in applied settings are small and easy to fake with a
badly-run A/B test. See experimental design,
sampling and
statistical inference.
Check who you excluded. A change that improves the average often hurts the tail; validate
against the neurodiversity guidance above.