Intelligence

What is Intelligence?

• Definition: The capacity to acquire knowledge, profit from experience, reason abstractly, and adapt purposefully to environmental changes.

• Core Debate: Unidimensional general intelligence ($g$) versus multidimensional distinct intelligences.

Classic Theories of Intelligence

• Charles Spearman (Two-Factor Theory):

  • Developed factor analysis.

  • General Factor ($g$): Overall mental capacity.

  • Specific Factors ($s$): Specific talents tailored to distinct tasks.

• Louis Thurstone (Primary Mental Abilities):

  • Rejected single-factor $g$; proposed seven independent primary abilities:

  • Word fluency, verbal comprehension, spatial visualization, perceptual speed, numerical ability, inductive reasoning, and associative memory.

• Raymond Cattell:

  • Fluid Intelligence ($Gf$): Raw problem-solving ability, pattern recognition, and abstract reasoning; independent of acquired education.

  • Crystallized Intelligence ($Gc$): Accumulated knowledge, vocabulary, and skills gained through education and experience.

History & Evolution of IQ Testing

• Binet-Simon Scale (Alfred Binet & Théodore Simon, 1905):

  • Designed to identify French schoolchildren requiring remedial instruction.

  • Composed of 30 items of increasing difficulty.

  • Introduced Mental Age (MA) relative to Chronological Age (CA).

  • Measured current academic performance rather than fixed innate potential.

• Henry Goddard (1908):

  • Translated the Binet scale into English and applied it to adults.

  • Misconstrued test results as fixed, innate potential, leading to unethical practices including forced sterilization and anti-immigration restrictions.

• Stanford-Binet Intelligence Scale (Lewis Terman, 1916):

  • Standardized American revision that became the benchmark test.

  • Initially emphasized verbal abilities; later integrated nonverbal metrics.

  • Terman launched a longitudinal study of $1500$ gifted children ("Termites", with $\text{IQ} > 150$) demonstrating that high IQ correlates with health, social adjustment, and adult success.

• Wechsler Intelligence Scales (David Wechsler):

  • Developed the WAIS (Adults, 1939) and WISC (Children).

  • Replaced quotient calculations with standardized deviation scores ($\mu = 100$, $\sigma = 15$).

Alternative Measures & Biological/Environmental Factors

• Raven’s Progressive Matrices:

  • Nonverbal abstract reasoning assessment measuring fluid intelligence independent of language or cultural bias.

• Reaction Range:

  • Genetics dictate the upper and lower boundaries of intellectual potential, whereas environmental quality determines where an individual falls within that range.

• The Flynn Effect:

  • A sustained generational increase in raw intelligence test scores across developed nations, necessitating periodic re-norming ($\mu = 100$) and underscoring the strong influence of environmental improvements (e.g., education, health, technology).

• Drudge Theory:

  • Proposes that extraordinary achievement is driven by determination, deliberate practice, and intensive training rather than innate ability alone.

Predictive Validity of IQ

• Predictive Correlates: High school and university GPA, occupational attainment, income level, job performance, longevity, self-regulation, perceptual discrimination speed, and neural conduction efficiency.

• Limitation: IQ measures current cognitive performance rather than immutable innate potential.

Multidimensional & Hierarchical Theories

• Unidimensional vs. Multidimensional:

  • Unidimensional models suggest competence in one cognitive area predicts success across all domains.

  • Multidimensional models suggest independent faculties, supported by selective brain injury (spared vs. lost functions) and Savant Syndrome (extraordinary isolated capability in a person with otherwise limited intellectual function).

• Gardner's Multiple Intelligences:

  • Argues for distinct intelligences (e.g., musical, kinesthetic, spatial, interpersonal).

  • Criticisms: Highly popular in education, but difficult to measure objectively; criticized for rebranding specific talents and personality traits as "intelligences."

• J.P. Guilford:

  • Postulated up to 150 distinct intellectual abilities.

• Sternberg's Triarchic Theory of Intelligence:

  • Three Facets of Intelligence:

  • Analytical: Abstract reasoning, evaluation, and academic problem-solving (captured by traditional IQ).

  • Creative: Generating novel ideas and reacting adaptively to new scenarios.

  • Practical: Solving everyday real-world problems using tacit knowledge (unwritten rules acquired via observation).

  • Three Componential/Subtheory Facets:

  • Contextual: Adapting behavior to the demands of specific environments.

  • Experiential: Automating familiar tasks and coping with novel situations.

  • Componential: Information-processing mechanisms, including knowledge-acquisition (encoding), performance (executing strategies), and metacognition (self-monitoring of cognitive processes; lower performers often overestimate their abilities).