Rapport du Task Force de APA
Intelligence: Knowns and Unknowns
Contexte politique et composition du groupe d’experts
The Board of Scientific Affairs (BSA) of the American Psychological Association had concluded that after the publication of The Bell Curve (1994) and the following debate that there were "serious misunderstandings" and "that there was urgent need for an authoritative report on these issues—one that all sides could use as a basis for discussion". Furthermore, "Another unfortunate aspect of the debate was that many participants made little effort to distinguish scientific issues from political ones, Research findings were often assessed not so much on their merits or their scientific standing as on their supposed political implications." The report stated that "The charge to our Task Force was to prepare a dispassionate survey of the state of the art: to make clear what has been scientifically established, what is presently in dispute, and what is still unknown. In fulfilling that charge, the only recommendations we shall make are for further research and calmer debate."[1]
It was originally published on August 7, 1995. It was authored by a task force of 11 experts. The APA Board on the Advancement of Psychology in the Public Interest (BAPPI) nominated one member of the Task Force. The Committee on Psychological Tests and Assessment nominated another. A third was nominated by the Council of Representatives. The other members were chosen by an extended consultative process with the aim of representing a broad range of expertise and opinion. Ulric Neisser was appointed Chair. Three of the experts were also among the 52 signatories to "Mainstream Science on Intelligence", a similar though much shorter statement of expert opinion on intelligence research findings published in 1994. Members of BSA and BAPPI were asked to comment on a preliminary draft of the report. The entire Task Force gave unanimous support to the final report. An edited version of "Intelligence: Knowns and Unknowns" was published in the journal American Psychologist in February 1996.
Sex Differences
Most standard tests of intelligence have been constructed
so that there are no overall score differences between females
and males. Some recent studies do report sex differences
in IQ, but the direction is variable and the effects
are small (Held, Alderton, Foley, & Segall, 1993; Lynn,
1994). This overall equivalence does not imply equal performance
on every individual ability. While some tasks
show no sex differences, there are others where small differences
appear and a few where they are large and
consistent.
Spatial and quantitative abilities.
Large differences favoring males appear on visual-spatial tasks like
mental rotation and spatiotemporal tasks like tracking a
moving object through space (Law, Pellegrino, & Hunt,
1993; Linn & Petersen, 1985). The sex difference on
mental rotation tasks is substantial: a recent meta-analysis
(Masters & Sanders, 1993) puts the effect size at d = 0.9.
(Effect sizes are measured in standard deviation units.
Here, the mean of the male distribution is nearly one
standard deviation above that for females.) Males'
achievement levels on movement-related and visual-spatial
tests are relevant to their generally better performance
in tasks that involve aiming and throwing (Jardine &
Martin, 1983).Some quantitative abilities also show consistent differences.
Females have a clear advantage on quantitative
tasks in the early years of school (Hyde, Fennema, & Lamon,
1990), but this reverses sometime before puberty;
males then maintain their superior performance into old
age. The math portion of the Scholastic Aptitude Test
shows a substantial advantage for males (d = 0.33 to 0.50),
with many more males scoring in the highest ranges
(Benbow, 1988; Halpern, 1992). Males also score consistently
higher on tests of proportional and mechanical reasoning
(Meehan, 1984; Stanley, Benbow, Brody, Dauber,
& Lupkowski, 1992).
Verbal abilities. Some verbal tasks show substantial
mean differences favoring females. These include
synonym generation and verbal fluency (e.g., naming
words that start with a given letter), with effect sizes ranging
from d = 0.5 to 1.2 (Gordon & Lee, 1986; Hines,
1990). On average females score higher on college
achievement tests in literature, English composition, and
Spanish (Stanley, 1993); they also excel at reading and
spelling. Many more males than females are diagnosed
with dyslexia and other reading disabilities (Sutaria,
1985), and there are many more male stutterers (Yairi &
Ambrose, 1992). Some memory tasks also show better
performance by females, but the size (and perhaps even
the direction) of the effect varies with the type of memory
being assessed.
Causal factors. There are both social and biological
reasons for these differences. At the social level
there are both subtle and overt differences between the
experiences, expectations, and gender roles of females and
males. Relevant environmental differences appear soon
after birth. They range from the gender-differentiated toys
that children regularly receive to the expectations of adult
life with which they are presented, from gender-differentiated
household and leisure activities to assumptions
about differences in basic ability. Models that include
many of these psychosocial variables have been successful
in predicting academic achievement (Eccles, 1987).
Many biological variables are also relevant. One focus
of current research is on differences in the sizes or
shapes of particular neural structures. Numerous sexually
dimorphic brain structures have now been identified, and
they may well have implications for cognition. There are,
for example, sex-related differences in the sizes of some
portions of the corpus callosum; these differences are correlated
with verbal fluency (Hines, Chiu, McAdams,
Bentler, & Lipcamon, 1992). Recent brain imaging studies
have found what may be differences in the lateralization
of language (Shaywitz et al., 1995). Note that such differences
in neural structure could result from differences
in patterns of life experience as well as from geneticallydriven
mechanisms of brain development; moreover,
brain development and experience may have bidirectional
effects on each other. This research area is still in a largely
exploratory phase.
Hormonal influences. The importance of prenatal
exposure to sex hormones is well established. Hormones
influence not only the developing genitalia but
also the brain and certain immune system structures
(Geschwind & Galaburda, 1987; Halpern & Cass, 1994).
Several studies have tested individuals who were exposed
to abnormally high androgen levels in utero, due to a
condition known as congenital adrenal hyperplasia
(CAH). Adult CAH females score significantly higher than
controls on tests of spatial ability (Resnick, Berenbaum,
Gottesman & Bouchard, 1986); CAH girls play more with
"boys' toys" and less with "girls' toys" than controls
(Berenbaum & Hines, 1992).
Other experimental paradigms confirm the relevance
of sex hormones for performance levels in certain skills.
Christiansen and Knussman (1987) found testosterone
levels in normal males to be correlated positively (about
.20) with some measures of spatial ability and negatively
(about -.20) with some measures of verbal ability. Older
males given testosterone show improved performance on
visual-spatial tests (Janowsky, Oviatt, & Orwoll, 1994).
Many similar findings have been reported, though the
effects are often nonlinear and complex (Gouchie & Kimura,
1991; Nyborg, 1984). It is clear that any adequate
model of sex differences in cognition will have to take
both biological and psychological variables (and their interactions)
into account.
