Brain mechanisms and intelligence. Psychometric g and executive function

Sternberg [Sternberg, R.J. (1985). Beyond IQ: a triarchic theory of human intelligence. New York: Cambridge Univ. Press.] has proposed that the general intelligence, or the g factor, obtained when batteries of mental tests are factor analyzed, is a reflection of the fact that executive functions (EF) are common to all cognitive tests. Three lines of evidence that fail to support Sternberg's formulation are presented. First, in animal problem solving studies, there is only a modest degree of overlap between brain structures that are critical for g, and brain structures that have been identified as the rodent EF system. Second, children with attention deficit-hyperactivity disorder (ADHD), characterized by EF dysfunction, do not have IQ scores that are lower, on average, than children in the test standardization populations. Third, human frontal lobe patients often have clear EF deficits, but IQ (a next-best estimate of g) may be preserved. These findings cast serious doubt on the plausibility of Sternberg's formulation. Clarifying the distinction between psychometric g and EF can be important for understanding the differences between practical and psychometric intelligence.