PSYC 1000 – Intelligence Testing & Theories (Study Notes)

Measuring Intelligence

  • Historical Foundations

    • Francis Galton’s Anthropometric Approach
    • Assumed superior sensory acuity ⇒ better learning ⇒ higher intelligence.
    • Devised anthropometrics = methods to quantify physical & mental variation.
    • Administered batteries of sensory tests (e.g., reaction time, visual acuity).
    • Empirical outcome: correlations between tests were weak/non-existent; sensory scores failed to predict academic achievement.
    • Significance: illustrated early empirical attempts but also the need for more valid constructs.

  • Modern Definition of Intelligence

    • "Ability to think, understand, reason, and adapt to overcome obstacles."
    • Emphasises complex cognition: memory, attention, comprehension, reasoning, knowledge accumulation, problem-solving.

  • Stanford–Binet Test

    • Originated (Alfred Binet & Théodore Simon) to identify French school-children needing support.
    • Core: tasks tapping higher-order cognition.
    • Introduced Mental Age (MA) = average intellectual level for a given chronological age.
    • Lewis Terman (Stanford) revised: framed scores as innate & fixed, renamed Stanford-Binet.
    • Ethical note: Terman & contemporaries used results to argue for eugenics & restrictive immigration.

  • Intelligence Quotient (IQ)

    • Classical formula IQ=MACA×100IQ = \frac{MA}{CA}\times100
    • Standardised so average =100=100.
    • Works for children; fails for adults (e.g., 4080×100=50\frac{40}{80}\times100 = 50 for an 8080-yr-old with MA 4040).
    • Deviation IQ: situates individual relative to same-age distribution (z-score style).

  • Wechsler Adult Intelligence Scale (WAIS)

    • Most widely used for adolescents & adults today.
    • Contains verbal comprehension, perceptual reasoning, working memory, processing speed indices.
    • Yields Full-Scale IQ plus profile across sub-indices.

  • Cultural Bias & Alternative Tests

    • Classical tests criticised for privileging majority language, schooling, cultural capital.
    • Raven’s Progressive Matrices: non-verbal pattern-completion tasks; intended to minimise linguistic/cultural loading.
    • Sample item: choose the missing piece out of 88 options to complete abstract matrix pattern (Answer for textbook fig. =6=6).
    • Despite such efforts, stable group mean differences persist; underscores complexity of culture, SES, stereotype threat.

  • Stereotype Threat

    • Mere awareness of a negative stereotype ⇒ anxiety ⇒ under-performance.
    • Demonstrates that the process of testing—context, framing, examiner identity—is itself a source of bias.

  • Implicit Theories of Intelligence

    • Entity theory: intelligence is fixed; errors ⇒ proof of low ability.
    • Incremental theory: intelligence is malleable; effort & strategies foster growth.
    • Mind-set manipulations alter persistence, course choices, and ultimately scores (“If you think you can, you might …”).

Understanding Intelligence

  • Spearman’s Two-Factor Theory

    • Statistical discovery: positive correlations across school subjects ⇒ general factor (g) = shared mental energy.
    • Specific factors (s) = skill/knowledge unique to particular tasks.
    • Correlates of g: higher academic success, longer life, better self-control, higher income, relationship quality; neuro-physiologically linked to faster & more efficient neuronal transmission.

  • Fluid (Gf) vs Crystallised (Gc) Intelligence

    • Gf: novel problem-solving, pattern recognition, mental flexibility; peaks in early adulthood then declines (e.g., solving unfamiliar geometric puzzles, improvising chess tactics).
    • Gc: accumulated knowledge & verbal skills; stable or improves with age (e.g., vocabulary, factual recall).
    • Interaction: higher Gf may scaffold acquisition of Gc over lifespan; empirically difficult to isolate pure Gf uncontaminated by Gc.

  • Beyond a Single g

    • Louis Thurstone: Seven Primary Mental Abilities
    1. Word fluency
    2. Verbal comprehension
    3. Numerical ability
    4. Spatial visualisation
    5. Memory
    6. Perceptual speed
    7. Reasoning
    • Factor-analytic work → Hierarchical model: tasks load onto specific abilities (s), which cluster into primary factors, all nested under higher-order g.

Biological Influences on Intelligence

  • Genetic Evidence

    • Twin & adoption studies: similarity in IQ rises with genetic relatedness.
    • Monozygotic twins reared together: r≈.90r\approx.90.
    • Monozygotic twins reared apart: r≈.80r\approx.80.
    • Dizygotic twins reared together: r≈.60r\approx.60.
    • Adoptive siblings (no shared genes): lowest correlations.
    • Heritability (population statistic): h2≈0.40–0.80h^2\approx0.40\text{–}0.80 for intelligence; however, magnitude is environment-dependent (e.g., higher in homogeneous, affluent contexts).

  • Behavioural Genomics

    • > 5050 genes individually explain tiny variance; polygenic scores aggregate small effects.
    • Gene-knockout (KO) studies: removing candidate gene in mice (e.g., affecting NMDA receptors) impairs spatial learning.
    • Transgenic studies: inserting or amplifying gene expression can enhance specific memory functions; reveals gene × environment interactions.

  • Brain Structure

    • Witelson et al. (2006): brain size accounted for 36%36\% of variance in verbal IQ—but only in women & right-handed men; no link to visuospatial IQ.
    • Cortical surface area & degree of gyrification correlate with intelligence across species (elephants, dolphins, primates) & within humans.

Environmental Influences on Intelligence

  • Enriched vs Impoverished Environments (Animal Models)

    • Rats reared with toys & social complexity: cerebral cortex 5%5\% larger, 25%25\% more synapses; learn mazes faster.
    • Implication: neuronal plasticity underpins experience-dependent intelligence gains.

  • Birth Order Effects

    • Mean trend: first-born > second > third in IQ by a few points.
    • Hypotheses: undivided parental attention early in life; teaching younger siblings deepens understanding.

  • Socioeconomic Status (SES)

    • Robust positive correlation with IQ.
    • Contributing pathways:
    • Language environment: higher SES children hear millions more words, richer vocabulary.
    • Parental engagement: scaffolding, educational materials, extracurriculars.
    • Reduced punishment / stressors leading to optimal neurodevelopment.
    • Sub-factors:
    • Nutrition
      • Diet high in saturated fat ⇒ cognitive decline; Mediterranean-style diets (fruit, veg, fish, whole grains) ⇒ higher cognitive functioning.
      • Avon Longitudinal Study of Parents and Children: early diet quality predicts later IQ.
    • Stress
      • Chronic stress elevates cortisol ⇒ impairs prefrontal cortex & hippocampus; worsens working memory & executive function.
    • Education
      • Duration & quality of schooling show direct positive association with IQ gains; school holidays often see temporary IQ dips.

  • Flynn Effect

    • Secular rise ≈ 33 IQ points/decade across many countries during 2020th century.
    • Candidate causes: improved nutrition, education, smaller families, more cognitively demanding environments (urbanisation, technology).
    • Negative Flynn Effect: recent plateau or reversal in some regions (e.g., Scandinavia); active debate—possible links to environmental toxins, testing changes, or shifts in schooling.

Ethical, Philosophical, & Practical Implications

  • Historical misuse: Galton, Terman, others harnessed IQ data to justify eugenics, forced sterilisations, immigration quotas—warnings about conflating descriptive statistics with prescriptive policy.
  • Impossibility of a completely culture-free test acknowledged; fairness requires awareness of stereotype threat, language loading, SES disparities.
  • Incremental mindset & enriched environments signal actionable levers for boosting cognitive performance, countering deterministic narratives.

Key Terms & Concepts Glossary

  • Anthropometrics: quantitative measurement of human traits.
  • Mental Age (MA), Chronological Age (CA).
  • Deviation IQ: standard score relative to age norms.
  • General Intelligence (g) vs Specific (s) abilities.
  • Fluid (Gf) / Crystallised (Gc) intelligence.
  • Heritability (h2h^2): proportion of variance attributable to genes.
  • Behavioural Genomics: field linking gene variants & behaviour.
  • Stereotype Threat, Entity/Incremental Theories.
  • Flynn Effect / Negative Flynn Effect.