IB Diploma Programme Psychology SL (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) and the cognitive approach (cognitive processes, the reliability of cognitive processes, emotion and cognition). 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.

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, explaining emotional responses that outrun conscious appraisal.

• 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).
• 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).

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.