How Thurstone Challenged Spearman’s General Intelligence (g) Theory

1) The Foundations of Spearman's g-Factor

In the early 1900s, Charles Spearman introduced the theory of general intelligence, known as the g-factor. This concept suggested that a single cognitive ability influences performance across diverse mental tasks, reflecting a unified capacity for reasoning and problem-solving.

Spearman used factor analysis, a statistical technique, to support his theory. By identifying patterns in the correlations between different cognitive tests, he proposed that these shared variations pointed to a common underlying factor—general intelligence.

The g-factor became a dominant model in psychology, influencing educational practices and cognitive testing for decades. However, its simplicity sparked questions about whether intelligence could truly be distilled into a singular construct.

2) Thurstone’s Critique of Spearman’s Methods

Louis Leon Thurstone challenged Spearman’s theory by questioning its methodological foundations. He argued that Spearman’s approach to factor analysis oversimplified the complexity of human intelligence, masking the diversity of mental abilities.

Thurstone enhanced factor analysis to reveal multiple distinct dimensions of intelligence. His research consistently identified clusters of abilities that were independent from one another, leading him to develop the concept of Primary Mental Abilities (PMAs), such as verbal comprehension, numerical ability, and spatial visualization.

This methodological refinement demonstrated that intelligence could not be reduced to a single factor. Thurstone’s findings paved the way for a broader understanding of cognitive capabilities.

3) Divergent Perspectives on Intelligence

The disagreement between Spearman and Thurstone highlighted two contrasting views of intelligence. Spearman’s model suggested a unifying factor, while Thurstone’s framework emphasized the independence of specific cognitive abilities.

Thurstone believed that correlations between tasks arose from the interplay of separate abilities rather than a general intelligence. For instance, success in both arithmetic and logic might reflect distinct yet overlapping skills.

This pluralistic view appealed to educators and psychologists who recognized significant variability in individuals’ cognitive strengths. It also aligned with observations of diverse learning styles and problem-solving strategies.

4) Implications of Thurstone’s Work

Thurstone’s contributions had a lasting impact on the study of intelligence. His Primary Mental Abilities model inspired subsequent theories that embraced a multifaceted view of cognitive abilities. This approach influenced educational testing and cognitive research, leading to assessments designed to evaluate specific skills.

While the debate between general and specific intelligence theories persisted, Thurstone’s work enriched the conversation, encouraging researchers to refine their methods and consider multiple perspectives.

Modern theories often integrate elements of both models, reflecting the complexity of human intelligence. Thurstone’s emphasis on methodological rigor and his multidimensional perspective remain influential in contemporary psychometric research.

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