The Answer Depends on the Question: A Reply to Eric Jensen

Abstract

THE QUESTION that Eric Jensen addresses in his article is whether brain research can provide a basis for educational practice. He debates John Bruer, president of the James S. McDonnell Foundation, and argues that brain research can, in fact, provide a basis for what educators do. Most of Jensen's article is devoted to showing ways in which brain research can provide a basis for educational interventions. Wrong question. The question is not whether educators can take brain-based or other biological research and derive educational implications from it. The right question is whether they can take such research and derive unequivocal educational implications. If not, then we have metaphor, but we do not really have science--or at least, not the kind of science that prescriptively is going to help us design educational interventions. Consider an important example. Is there a general ability that dominates over all others, (1) or are there multiple intelligences, each relatively independent of the others, that work in tandem with one another, but that are coequal in importance? Howard Gardner has presented an impressive array of neuropsychological evidence in favor of multiple intelligences. (2) This work is cited and discussed in the Jensen article. At the same time, John Duncan has supplied targeted evidence in support of a general factor and has even identified in the brain the alleged loci in the lateral frontal cortex. (3) Duncan's initial article was published in Science, one of the most prestigious journals in all of the sciences. A second article was published in another highly prestigious journal, Cortex. There is actually a much more extensive literature claiming that general intelligence can be localized in one part or another of the frontal cortex. So what can we conclude from brain research? We can conclude either that children can be ordered on a unidimensional scale that pretty much captures their different abilities to succeed in school, or we can conclude the opposite. Thus brain research does indeed have implications for education. What they are, however, depends in large part upon one's preferred ideology. Okay, maybe I picked a loser example. So let's try another question. Is intelligence correlated with brain size? Stephen Jay Gould ridiculed this notion and claimed that the evidence for it was absurd. (4) Yet there is evidence that suggests that there is a relationship. The idea that the size of the brain may relate to intelligence was proposed by Paul Broca nearly a century and a half ago and was reintroduced by Francis Galton a generation later. (5) Brain size is a rough proxy for processing capacity, but a proxy for brain size is head size. The correlation between head size and brain size in adults has been estimated variously, with .60 a typical estimate. (6) In infants and young children, the correlation is higher. (7) Generally positive correlations have been found between various measures of head size and I.Q. A meta-analysis of 35 studies with 54 independent samples and 56,793 participants revealed correlations ranging from .02 to .54, with a mean of .19. (8) Thirty-six of the 54 correlations were statistically significant. Of course, a more accurate estimate of the relationship of brain size to I.Q. can be obtained by using brain-imaging techniques that directly study the size of the brain. A meta-analysis of 15 samples with a total N of 657 revealed an unweighted mean correlation of .40. These data suggest, again, that there is some correlation. Where do these results leave us? Well, it appears that either there is or there is not a relationship between brain size and intelligence. Let's say, for the sake of argument, there is. What is the cause? Perhaps that is the more important question. Why do people have different head or brain sizes? Experience plays some role. Work by William Greenough and by Marian Diamond shows that experience can alter the structure and therefore the function of the brain. …