Brain mechanisms and intelligence. Psychometric g and executive function

Sternberg [Sternberg, R.J. (1985). Beyond IQ: a triarchic theory of human i ntelligence. New York: Cambridge Univ. Press.] has proposed that the genera l intelligence, or the g factor, obtained when batteries of mental tests ar e 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 s upport Sternberg's formulation are presented. First, in animal problem solv ing studies, there is only a modest degree of overlap between brain structu res that are critical for g, and brain structures that have been identified as the rodent EF system. Second, children with attention deficit-hyperacti vity disorder (ADHD), characterized by EF dysfunction, do not have IQ score s that are lower, on average, than children in the test standardization pop ulations. Third, human frontal lobe patients often have clear EF deficits, but IQ (a next-best estimate of g) may be preserved. These findings cast se rious doubt on the plausibility of Sternberg's formulation. Clarifying the distinction between psychometric g and EF can be important for understandin g the differences between practical and psychometric intelligence.