who proposed the concept of primary mental abilities
Louis Leon Thurstone Thurstone's work in factor analysis led him to formulate a model of intelligence center around "Primary Mental Abilities" (PMAs), which were independent group factors of intelligence that different individuals possessed in varying degrees. He opposed the notion of a singular general intelligence that factored into the scores of all psychometric tests and was expressed as a mental age. In 1935 Thurstone, together with EL Thorndike and JP Guilford founded the journal Psychometrika and also the Psychometric Society, going on to become the society's first President in 1936. Thurstone's contributions to methods of factor analysis have proved valuable in establishing and verifying later psychometric factor structures, and has influenced the hierarchical models of intelligence in use in intelligence tests such as WAIS and the modern Stanford-Binet IQ test.[7]
Gestalt psychology The concept of gestalt was first introduced in philosophy and psychology in 1890 by Christian von Ehrenfels (a member of the School of Brentano). The idea of gestalt has its roots in theories by David Hume, Johann Wolfgang von Goethe, Immanuel Kant, David Hartley, and Ernst Mach. Max Wertheimer's unique contribution was to insist that the "gestalt" is perceptually primary, defining the parts it was composed from, rather than being a secondary quality that emerges from those parts, as von Ehrenfels's earlier Gestalt-QualitÃ¤t had been.[citation needed]