John B. Carroll’s theory of the three layers of intelligence proposes that the factorial structure of human cognitive abilities is composed of a general intellectual capacity (the g factor), a set of 8 broad abilities, such as speed of mental processing or memory, and a third layer that would include more specific intellectual abilities dependent on one of the previous ones.

In this article, we will analyze Carroll’s model, which today is often studied and applied in conjunction with the theory of fluid and crystallized intelligences proposed by Cattell and Horn. We will focus in particular on the analysis of each of the strata of intelligence described by this author.

John Carroll’s theory of intelligence

The American psychologist John Bissell Carroll (1916-2003) is mainly known for his contributions in the field of psychometry around the measurement of phenomena such as intelligence, language skills or academic performance. On the other hand, his theoretical approaches to cognition and language are also very relevant.

Particularly noteworthy is its theory of the three layers, a model based on the results of hundreds of factor analyses on samples of numerical data that can serve as predictive variables of intelligence, such as IQ tests or scores obtained in academic assessment tests.

Carroll presented the results of his studies together with his theory of intelligence in the work entitled “Human Cognitive Abilities: An Investigation of Analytical-Factorial Studies”, which was published in 1993. In this book he emphasized the distinction between skills related to individual differences and those derived from the quality of education.

At present, Carroll’s theory of three layers is considered complementary to the model of Raymond B. Cattell and John L. Horn (centred on the division between fluid and crystallised intelligence), which Carroll himself had defended before creating his own. The assimilation of both perspectives into one can be attributed to Kevin McGrew (2012).

The Three Strata of Cognitive Ability

Carroll’s theoretical proposal can be included in the category of hierarchical models on intelligence, since it describes three layers that go from the most specific samples of cognitive ability to its general aspect, which is specified in the “g-factor” construct. According to the author, these aptitudes would have a stable character.

Carroll stated that these capabilities can probably be attributed to physiological variables . In this sense, it is worth mentioning that authors such as Philip Vernon (who developed his own theory on the structure of intelligence) and Hans Eysenck have related cognitive abilities to the efficiency and quality of neuronal transmission.

1. First Stratum: Primary Mental Abilities

According to Carroll, the lower stratum of the intelligence structure is made up of primary mental abilities, which include a large number of cognitive abilities: quantitative reasoning, spelling, visualization ,aptitude for foreign languages, discrimination of speech sounds, fluency of ideas, reaction time, etc.

The results of the factor analyses handled by Carroll and other later authors reveal that each of these aptitudes, which have a high degree of specificity, weigh in one of the complex factors of the second layer depending on the characteristics of the material stimulated and the overall skill on which they depend.

2. Second layer: complex factors

At this level we find a broad set of cognitive skills. Carroll originally proposed the presence of 10 factors in the second stratum, although later research reduced the number to 8:

  • Fluid intelligence: ability to reason and solve problems using new information.
  • Crystallized intelligence: refers to the depth and amount of verbal knowledge acquired and the handling of this type of data.
  • General memory and learning: ability to learn in general along with specific skills such as retaining information or recovering it in the short term.
  • Comprehensive resilience: includes the skills to handle ideas and associations fluently, both verbally and in images.
  • Visual processing: ability to perceive, analyze, remember and operate with visual stimulation.
  • Auditory processing: the ability to discriminate and process sounds, including those associated with speech and music
  • Broad cognitive speed: refers to the speed of handling the stimuli during the tests (e.g. the numbers) and completing them.
  • Processing speed : ability to execute automatic cognitive processes, particularly by maintaining selective attention.

Each of these factors encompasses several lower order factors corresponding to the first stratum. Thus, for example, crystallized intelligence includes reading comprehension, spelling and foreign language ability, while broad resilience is derived from tests of creativity and fluency with different types of material.

3. Third stratum: general intelligence or g-factor

The third layer of the structure defined by Carroll is constituted by the general intelligence factor , a construct known as the “g factor” and which is used by a large number of psychologists. This higher order aptitude would influence all the aptitudes included in the second stratum, and therefore also those of the third stratum in an indirect manner.

Bibliographic references:

  • Carroll, J. B. (1993). Human cognitive abilities: A survey of factor-analytic studies. New York: Cambridge University Press.
  • Hogan, T. P. (2004). Psychological testing: A practical introduction. Buenos Aires: Manual Moderno.
  • Horn, J. & Cattell, R. (1966). Refinement and test of the theory of fluid and crystallized general intelligences. Journal of Educational Psychology, 57: 253-70.
  • McGrew, K. (2012). Cognitive abilities. In D. P. Flanagan & P. L. Harrison (Eds.), “Contemporary intellectual assessment: Theories, tests, and issues”. New York: Guilford Press.