IB Diploma Programme Psychology HL (first assessment 2021; current guide). This topic covers the CORE's first two approaches in full: the biological approach (the brain and behaviour, hormones and behaviour, genetics and behaviour, plus the HL-only role of animal research) and the cognitive approach (cognitive processes, the reliability of cognitive processes, emotion and cognition, plus the HL-only digital world). Every claim below travels with a named study — in IB psychology an unaccompanied theory earns nothing. The worked numbers are the published findings of the classic studies, rounded where noted.

Must-know for the core approaches:

The biological approach 生物取向 explains behaviour by physiological processes: brain structures, brain chemistry and genetics — thought, feeling and action are what the body does. Localisation of function 功能定位 holds that specific brain areas do specific jobs; the case of Phineas Gage (iron rod through the frontal lobe, 1848; personality changed, faculties otherwise intact) and patient H.M. (surgery removed the hippocampi, 1953; new long-term memories never formed, procedural memory intact) are the classic case studies — rich in detail, and exactly as limited as any n = 1. Neuroplasticity 神经可塑性 is the brain's remodelling with use: Maguire et al. (2000) found London taxi drivers' posterior hippocampi larger than controls', growing with years of navigation — but taxi driving also differs in a dozen other ways, so the fMRI correlation is not causation. TECHNIQUES: fMRI shows activation (spatial, indirect, correlational); EEG/ERP shows timing (temporal, but the skull smears the source); MRI shows structure; post-mortem examination confirms anatomy after death.

Hormones 激素 are chemical messengers: chronic CORTISOL elevation under stress impairs hippocampal memory; TESTOSTERONE relates to aggression (Dabbs et al. found higher salivary testosterone among violent offenders than non-violent — a correlation with many confounds); OXYTOCIN rises with trust and bonding (Kosfeld et al., 2005: nasal oxytocin raised trust-game transfers — a small, induced, laboratory effect). Genetics and behaviour: genes set ranges, not destinies. Twin studies compare identical (MZ) with fraternal (DZ) twins — schizophrenia concordance runs near 50% for MZ against roughly 15–20% for DZ (Gottesman): substantial heritability, and equally clear non-heritability, since identical genes do not guarantee the outcome. The gene–environment interaction 基因环境交互作用 is Caspi et al. (2003): among people suffering severe life stress, depression followed for about 33% of those carrying two short 5-HTT alleles against about 17% of those with two long alleles — the gene matters only in its environment. HL EXTENSION — ANIMAL RESEARCH: Harlow's rhesus monkeys (wire versus cloth mothers) established contact comfort where human experiments could never run; the debate is the 3Rs (replace, reduce, refine) against generalising from rat and monkey brains to human minds.

The cognitive approach 认知取向 treats the mind as an information processor — input, encoding, storage, retrieval, output — studied rigorously since the 1950s "cognitive revolution". MEMORY MODELS: the MULTI-STORE model (Atkinson–Shiffrin) separates sensory, short-term and long-term stores; its evidence includes the serial position curve (primacy from the long-term store, recency from the short-term store — and recency vanishes after a short filled delay, Glanzer–Cunitz 1966). Working memory 工作记忆 (Baddeley–Hitch) replaces a single short-term store with an executive plus slave systems, predicting the word-length effect (fewer long words recalled — articulatory rehearsal is time-limited). Schema theory: knowledge is organised in schemas 图式 that guide encoding and retrieval; Bartlett's "War of the Ghosts" (1932) showed participants reshaping an unfamiliar story toward their own cultural schemas on every retelling — memory is reconstructive 重构记忆, not a videotape.

RELIABILITY: leading questions 引导性问题 distort recall — Loftus and Palmer (1974): watching the same crash, participants estimated 40.8 mph for "smashed" against 34.0 mph for "hit", and a week later more of the "smashed" group "remembered" broken glass that never was. But Yuille and Cutshall (1986) found real witnesses of a shooting highly accurate months later — high stress, real event, no leading interviewer: reliability depends on conditions, not a fixed human flaw. BIASES: the availability heuristic judges frequency by ease of recall (Tversky–Kahneman), so vivid events feel common. EMOTION AND COGNITION: Brown–Kulik's FLASHBULB memories feel photographic — but Neisser and Harsch (1992) found Challenger-shuttle memories changed substantially over 32 months while confidence stayed high: vivid is not accurate. LeDoux's two routes — a fast amygdala path and a slower cortical path — explain emotional responses outrunning conscious appraisal. HL EXTENSION — THE DIGITAL WORLD: Sparrow et al. (2011) found people remember WHERE information is stored rather than the information itself when they expect future access (the "Google effect") — a transactive-memory redistribution, not an atrophied brain.

• Localisation with Gage and H.M.; neuroplasticity with Maguire; the four techniques and what each can and cannot show (biological).
• Cortisol, testosterone (Dabbs) and oxytocin (Kosfeld) as correlational messengers (biological).
• Twin studies (MZ/DZ concordance) and Caspi's 5-HTT interaction; genes as ranges, not destiny (biological).
• HL: Harlow and the 3Rs; the generalisability debate (biological).
• Multi-store with the serial position curve; working memory with the word-length effect; schema theory with Bartlett (cognitive).
• Leading questions with Loftus–Palmer's 40.8/34.0 mph and the Yuille–Cutshall counterpoint; availability bias (cognitive).
• Flashbulb memory (Brown–Kulik, Neisser–Harsch) and LeDoux's two routes (cognitive).
• HL: the Google effect (Sparrow) and transactive memory (cognitive).

Boundary notes: Paper 1 Section A (short-answer, [9]) rewards ONE accurate study per approach named precisely — researcher, method, finding; Section B essays ([22]) require evaluation — strengths, limitations and the assumption each study rests on. All study findings cited are the published classic results; where they are rounded, the direction and gap are as reported.