Cognitive Intelligence

2.1 Defining and Measuring Intelligence

The study of intelligence began in earnest with Alfred Binet and Théodore Simon (1905) in France, who developed the first standardised test to identify students needing special educational support. Their scale measured Mental Age (MA) — the level of cognitive tasks a child could perform regardless of chronological age.

William Stern (1912) introduced the Intelligence Quotient (IQ):

IQ = (Mental Age / Chronological Age) × 100

Lewis Terman (1916) at Stanford University revised the scale (Stanford-Binet test) and popularised IQ. An IQ of 100 = average; 130+ = gifted; below 70 = intellectual disability.

David Wechsler (1939) developed the Wechsler-Bellevue Intelligence Scale for adults (later WAIS — Wechsler Adult Intelligence Scale), which moved beyond verbal tests to include performance subtests (block design, picture arrangement, object assembly). Wechsler defined intelligence as "the aggregate or global capacity of the individual to act purposefully, to think rationally, and to deal effectively with his environment" (1944). This definition is the most cited in RPSC PYQs.

2.2 Theories of Cognitive Intelligence

Spearman's Two-Factor Theory (1904):

• 'g' factor (general intelligence): A single underlying mental energy common to all cognitive tasks. Correlations between diverse mental tests suggested a common factor.
• 's' factors (specific intelligence): Domain-specific abilities (verbal, numerical, spatial) that differ per task.
• Method: Factor Analysis — statistical technique Spearman pioneered.

Thurstone's Primary Mental Abilities (1938):
Louis L. Thurstone challenged Spearman's single 'g', proposing 7 primary mental abilities: Verbal Comprehension, Word Fluency, Number Facility, Spatial Visualisation, Associative Memory, Perceptual Speed, and Inductive Reasoning. IQ tests should measure each separately.

Guilford's Structure of Intellect Model (1967):
J. P. Guilford proposed a 3-dimensional model with 180 distinct intellectual abilities (later expanded to 150): Operations (6) × Contents (5) × Products (6). Creativity was included as divergent thinking — ability to generate multiple solutions.

Cattell's Fluid and Crystallised Intelligence (1963):
Raymond Cattell proposed two components:

• Fluid intelligence (Gf): Ability to reason and solve novel problems; peaks in early adulthood; declines with age. Not dependent on prior knowledge.
• Crystallised intelligence (Gc): Accumulated knowledge and verbal skills from experience; increases with age. Measured by vocabulary and general knowledge tests.

2.3 Memory — The Foundation of Cognitive Intelligence

The Atkinson-Shiffrin Multi-Store Memory Model (1968) remains the most exam-relevant framework:

Stage	Duration	Capacity	Key Feature
Sensory Memory	< 1 second (iconic) / 3–4 seconds (echoic)	All sensory inputs simultaneously	Filters — only attended items move to STM
Short-Term Memory (STM)	15–30 seconds (without rehearsal)	7±2 items (George Miller, 1956)	Rehearsal extends duration; chunking increases capacity
Long-Term Memory (LTM)	Potentially permanent	Unlimited	Divided into explicit (declarative) and implicit (procedural)

LTM subtypes:

• Semantic: General knowledge and facts (e.g., "Paris is the capital of France")
• Episodic: Personal experiences tied to time/place (e.g., "My first day at work")
• Procedural: Motor skills and automatic processes (e.g., cycling, typing)

Forgetting theories:

• Trace Decay: Memory trace fades over time through disuse (Hermann Ebbinghaus, 1885 — the forgetting curve)
• Interference: Proactive interference (old memories block new) vs. Retroactive interference (new memories block old)
• Retrieval Failure: Information exists in LTM but retrieval cues are absent (Tip-of-the-tongue phenomenon)

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