Intelligence: Definitions, Theories, Testing, Biology, Environment, and Extremes

Learning Objectives

• Accurately define and differentiate various conceptions of intelligence.
• Explain the debate over whether intelligence is general (one overarching factor) or domain-specific.
• Describe psychometric principles (reliability, validity, standardization) that guide test construction.
• Recount the historical development of intelligence testing and related controversies (eugenics, cultural bias).
• Outline modern multifactor theories (Gardner, Sternberg, Ceci) and additional proposed intelligences (emotional, social, wisdom, creativity).
• Summarize biological and environmental contributions to intelligence, how these factors shape public policy, and their neural correlates.
• Describe how brain size, neuron count, processing speed, neural efficiency, entropy, and cortical maturation correlate with IQ.
• Identify the diagnostic criteria, causes, and life outcomes associated with intellectual disability and giftedness.

Foundational Questions About Intelligence

• How do we distinguish intelligence from talent?
• Is intelligence equal to wisdom? Creativity?
• How is intelligence valued across cultures and situations?

Core Definitions

• Intelligence: the capacity to learn, meet environmental demands effectively, and understand/​control one’s own cognitive processes.
• Metacognition: awareness and regulation of one’s thinking; often considered a crucial component of intelligence.

Is Intelligence General or Specific?

Spearman’s Two-Factor Theory

• Used factor analysis to examine correlations among test items.
  • Items that correlate highly form a cluster (shared variance).
• Proposed two sources of variance in any mental-ability task:
  • g factor (general intelligence): a single, overarching ability that underlies performance on all mental tasks.
  • s factors (specific abilities): unique skills tied to particular tasks (e.g., arithmetic, verbal fluency).
  • Diagram in lecture showed a central g node connected to eight s nodes (S₁ – S₈).

Thurstone’s Primary Mental Abilities

• Seven relatively independent abilities:
  • Verbal comprehension
  • Word fluency
  • Numerical skill
  • Spatial ability
  • Associative memory
  • Perceptual speed
  • Reasoning

Modern Multifactor Theories

Gardner’s Theory of Multiple Intelligences

• Rejects a single IQ; posits independent intelligences tied to specific brain regions.
• Listed intelligences:
  • Linguistic
  • Logical/​mathematical
  • Musical
  • Spatial
  • Bodily/​kinesthetic
  • Interpersonal
  • Intrapersonal
  • Naturalistic
  • Existentialist (added later by Gardner)

Sternberg’s Triarchic Theory

1. Internal / Analytic: conventional academic problem-solving; heavily sampled by IQ tests.
2. External / Creative: dealing with novel tasks, generating innovative ideas.
3. Experiential / Practical: adapting to, shaping, or selecting environments ("street smarts").

• Illustrated as three interacting components (Analytic ↔ Creative ↔ Practical).

Ceci’s Bioecological Model

• Intelligence emerges from an interaction among:
  • Biology (innate potential)
  • Environment (ecological context)
  • Motivation (internal drive)
• Depicted as overlapping circles (Biology, Environment, Motivation).

Measuring Intelligence: The Psychometric Approach

• Goal: construct standardized tests that yield quantitative scores of intellectual performance.

Key Test-Construction Concepts

• Reliability: consistency of scores.
  • Test–retest reliability: same person, two administrations.
  • Split-half reliability: correlate performance on two halves of the same test.
• Validity: does the test measure what it claims?
  • Content validity: test content represents the domain.
  • Predictive validity: score forecasts future performance.
  • Measured via a validity coefficient (correlation with external criterion).
• Standardization: uniform procedures for administration & scoring; creation of norms.
• Normal distribution: bell-shaped curve; most scores cluster near the mean.
  • Empirical rule: 68 % within ±1 SD, 95 % within ±2 SD.
• Measures of central tendency on a normal curve:
  • Mean (average)
  • Median (middle score)
  • Mode (most frequent)

Historical Milestones in Intelligence Testing

1. Alfred Binet & Théodore Simon
   • Developed language-based test to identify French children needing help.
   • Introduced mental age concept.
2. Lewis Terman (Stanford University)
   • Adapted Binet–Simon for U.S.; created Stanford–Binet.
   • Coined Intelligence Quotient (IQ): IQ = \frac{\text{mental age}}{\text{chronological age}} \times 100.
3. Francis Galton
   • Believed higher "psychic energy" & sensory acuity signaled genius.
   • Built lab tests of reaction time, sensory discrimination; conceptually linked to eugenics.
4. Eugenics Movement (dark side)
   • Used IQ to judge reproductive "fitness" of immigrants & army recruits (Terman’s era).
5. David Wechsler
   • Noted mental-vs-chronological-age gap loses meaning in adults.
   • WAIS-IVCDN: verbal, working-memory, perceptual-reasoning & processing-speed indices.
   • Numerous subtests (e.g., Vocabulary: "What does repudiate mean?"; Block Design; Digit Span; Symbol Search). Designed for fairer testing of non-native English speakers.

Predictive Utility of IQ Tests

• Stanford-Binet & WAIS display high reliability and predict:
  • School grades and total years of education.
  • To a lesser degree: occupational prestige, income, health behaviors, longevity.
• Relationships are correlational, not causal.

Cultural Bias & Stereotypes

• Average score differences among racial/​ethnic groups on traditional IQ tests.
• Potential explanations: test bias, socioeconomic factors, stereotype threat.
• Example of culturally loaded item: "Caesar is to salad as _ is to brandy" (answer: Napoleon).
• Raven’s Progressive Matrices created to reduce cultural content—focus on abstract, non-verbal reasoning.

The Flynn Effect

• Steady worldwide rise (~3 points/decade) in average IQ since early 20th century.
• Puzzling because many scholastic achievement scores have fallen, highlighting test-specific gains & environmental influences (nutrition, schooling, complexity of modern life, etc.).

Additional Proposed Intelligences

• Emotional Intelligence: perceive, use, understand, and regulate emotions; involves empathy & self-control.
• Social Intelligence: navigate social environments effectively, build relationships.
• Wisdom: make sound, morally informed judgments; seen as an outgrowth of practical intelligence.
• Creativity: generate novel, valuable ideas; fueled by intrinsic motivation, imagination, playful "game" personality.
• Lecture reminder: "Intelligence is the cognitive part of personality."

Biological & Environmental Influences

The Bell Curve (Herrnstein & Murray, 1994)

• Controversial claims:
  1. IQ tests validly measure intelligence.
  2. IQ predicts success metrics (school, job, parenting, income, crime avoidance).
  3. Society is sorting into a "cognitive elite" based on IQ.
  4. Testing should gate access to opportunities.
  5. IQ is largely heritable.
  6. Average racial/ethnic IQ gaps exist.
  7. Differences likely partly genetic.

Genetic Evidence

• Twin correlations: identical r \approx 0.86; fraternal r \approx 0.60.
• Heritability coefficient (h²): proportion of variance due to genes (value context-specific; rises in affluent settings, falls in deprived ones).

Environmental Evidence

• Family & home dominate early childhood outcomes.
• Culture shapes definitions & valued expressions of intelligence (e.g., hunting skill vs. academic reasoning).
• Occupation: complex jobs ↔ higher intelligence (bidirectional).
• Schooling: both consequence & cause of IQ; extended education boosts cognitive skills.
• Group differences analogy: same seeds planted in two soils → group mean differences reflect environment, not seed quality.

Enrichment Interventions

• Early, intensive, prolonged programs yield the greatest IQ gains, but mainly for children from deprived backgrounds.
• Must incorporate attitude & behavior supports to maintain benefits.

Neural Correlates of Intelligence

• Larger brain size & greater neuron count in frontal lobes correlate with higher IQ.
• Processing speed: fast sensory/​motor responses (measured via EEG) predict higher scores.
• Neural efficiency hypothesis: bright brains show lower metabolic activity during easy tasks (less effort).
• Brain entropy: breadth of neural configurations accessible during problem solving—higher entropy may underlie flexibility.
• Cortical maturation: highly intelligent children exhibit prolonged thickening & later pruning of cortex, suggesting extended period of circuit refinement.

Extremes of Intelligence

Distribution

• Normal curve with mean 100; SD 15.
• Population percentages:
  • \pm 1 SD (85–115): 68 %
  • \pm 2 SD (70–130): 95 %
  • <70: ~2.3 % (intellectual disability)
  • >130: ~2.3 % (gifted)

Intellectual Disability (ID)

• General criterion: IQ <70 plus deficits in adaptive functioning.
• Mild ID (largest subgroup)
  • Usually detected at school entry; often environment related; can achieve independent adult life.
• Moderate ID
  • Diagnosed earlier; communicate adequately; perform semi-skilled work under supervision.
• Severe ID
  • Motor & language delays; vulnerable to seizures; require close supervision; can do basic tasks in structured settings.
• Profound ID
  • Noticeable at birth; require highly structured, one-on-one care.
• Down Syndrome
  • Extra material on 21st chromosome; prevalence

Giftedness

• Top 1–2 % of population (>130 IQ or exceptional talent).
• Often intrinsically motivated; environmental support critical; may show domain-specific strengths (e.g., emotional vs. analytic).
• Example: Michael Kearney, who earned a bachelor’s at age 10.

Ethical, Social, & Policy Implications

• Misuse of testing (eugenics, immigration, military screening) underscores need for culturally sensitive assessment.
• Overemphasis on heredity can lead to deterministic policies; overemphasis on environment may ignore biological constraints.
• Balanced view: intelligence arises from dynamic interplay of genes, environment, motivation, and culture.

Key Equations & Statistics

• Intelligence Quotient: IQ = \frac{\text{mental age}}{\text{chronological age}} \times 100
• Twin correlations: identical r = 0.86; fraternal r = 0.60.
• Normal-curve rule: 68 % within \pm 1 SD, 95 % within \pm 2 SD.

Study Tips

• Relate theories (Spearman, Gardner, Sternberg) to real-world tasks you perform daily.
• Practice interpreting IQ-related statistics (heritability, SDs, correlations).
• Critically examine historical misuse of testing to understand ethical responsibilities of psychologists.
• Link neural efficiency & cortical maturation findings with developmental milestones you learned in earlier lectures.
• Apply emotional & social intelligence concepts to group projects or workplace scenarios to solidify understanding.