This is one of the largest groups in the ledger, and it runs from nineteenth-century laboratories to findings published in the last decade. It holds some of the most secure results in science and some of the most famous failures. Reading the group well means knowing which is which, and it is the one group in the ledger where that question is itself a subject of research.
The foundations
The oldest findings are also the most durable. The Weber–Fechner Law and Stevens's Power Law relate physical intensity to felt intensity. Ebbinghaus's Forgetting Curve and the Serial Position Effect describe memory's shape. Pavlovian Conditioning, Thorndike's Law of Effect and Schedules of Reinforcement describe learning by consequence. The Gestalt laws, from Proximity to Prägnanz, describe how the eye groups what it sees. These have been reproduced for more than a century.
Memory reconstructs
A large cluster shows memory rebuilding the past rather than replaying it. The DRM False-Memory Effect produces confident memories of words never presented. Imagination Inflation, Source-Monitoring Errors and Memory Conformity show imagined events, misremembered sources and other people's accounts entering what a person believes they saw. Change Blindness and Inattentional Blindness add that people often fail to see what was in front of them to begin with.
Influence and the social self
The social findings are the ones most people know. Asch Conformity, Group Polarization and Social Loafing describe what groups do to individual judgement and effort. Cialdini's catalogue of influence, from the Foot-in-the-Door and Door-in-the-Face techniques to the Liking Principle, documents how compliance is produced. A long list describes how people misjudge themselves: Illusory Superiority, the Spotlight Effect, the Curse of Knowledge and the Typical Mind Fallacy. Group identity adds In-Group Favouritism and the Out-Group Homogeneity Effect.
Feeling and remembering feeling
A final cluster concerns wellbeing. The Peak-End Rule and Duration Neglect show experiences remembered by their most intense moment and their ending, not their length. Hedonic Adaptation, Immune Neglect and the Hot–Cold Empathy Gap explain why people mispredict how they will feel. Negativity Bias gives bad events more weight than good ones of the same size.
Where it applies
The applications are everywhere. Courts rely on eyewitness testimony that the memory findings show to be fragile, and several jurisdictions now caution juries accordingly. Designers use the Gestalt laws daily. Salespeople and fundraisers use Cialdini's techniques, which makes knowing them a form of self-defence. The peak-end rule has been used to redesign medical procedures and customer experiences so that they end well.
Where it is argued over
This subject sits at the centre of the replication crisis. A 2015 attempt to reproduce 100 published psychology studies succeeded for fewer than half. In this group, the Lady Macbeth Effect and Moral Licensing have largely failed replication; the Milgram and Hawthorne studies have been challenged on their original data; and the Dunning–Kruger Effect is partly reproducible from statistical noise. A second criticism concerns samples: much of this research used Western university students, whom Henrich and colleagues showed to be unusual on many measures. The ledger's contested flags mark where these disputes are live.
Why it is worth knowing
These findings describe the equipment every person uses to perceive, remember and judge. Knowing them does not remove their effects, but it changes what a person trusts: a vivid memory, a confident eyewitness, a group's unanimity or one's own sense of being above average. Knowing which findings have held and which have not is a lesson in itself, since it shows how a science corrects its own mistakes.
The entries behind this essay: Evidence in Psychology & Behavior. Every subject has its essays on the essays page.