same in spring as in autumn. Apparently, average to below-average levels of
testosterone are associated with optimal performance on visual-spatial tasks in
men (Gouchie & Kimura, 1991).
What is it that sex hormones do to the brain that gives rise to differences in
cognition? One possibility is that hormones affect how the cerebral hemispheres
distribute their function. Recall that in most people the left hemisphere is more
involved than the right in the control of language whereas the right hemisphere
is more involved than the left in the control of spatial processing. Perhaps the
female advantage for some verbal skills reflects the involvement of more right-
hemisphere neural tissue in language–neural tissue that at the same time
encroaches on the neural tissue that would have been used for spatial process-
ing. At least some evidence suggests that there is less tendency among women
for their left hemisphere to control language more than their right hemisphere
(e.g., Shaywitz et al., 1995), although not all studies find a sex difference
in hemispheric specialization (Newcombe & Bandura, 1983; Waber, Mann,
Merola, & Moylan, 1985).
Another possible neurological model of sex hormone differences in brain or-
ganization has been developed by Kimura (1992). Kimura suggests that the or-
ganization of functions within the left hemisphere differs between the sexes. For
language functions, women may make more use of the anterior portions of the
left hemisphere whereas men make more use of the posterior left hemisphere.
Such a difference may give rise to the tendency for women to do better on tests
of verbal fluency, because the grammatical aspect of language may be more
anatomically connected to the planning and strategic components of informa-
tion processing. The more intimate connection in males between language cen-
ters and the centers involved in visual perception may give rise to the male
advantages on spatial reasoning tasks. One line of evidence consistent with this
view is that aphasia (language disturbance) occurs more often in women when
the damage is near the front of the left hemisphere, but more often in men
when the damage is in the posterior area of the left hemisphere (Kimura, 1992).
It is important to point out that the supposed differences in the brains of men
and women may not necessarily reflect the effects of sex hormones; those dif-
ferences may be mediated by some other biological mechanism. Furthermore,
the sex differences in relevant biological mechanisms need not be entirely or
even at all due to genes. It may be that experiences, like playing with toys or
studying mathematics, affect the production of hormones (and any other rele-
vant biological mechanism) and thereby produce sex differences in certain cog-
nitive skills.
Environmental Explanations of Sex Differences in Cognition My own belief is that
it remains a viable possibility that sex differences in cognition are due mostly to
environmental factors (how is that for a hedge!). One line of evidence for an
environmental explanation of sex differences is that parental attitudes and
expectations are correlated with performance on math (Raymond & Benbow,
1986) and verbal tests (Roe, Drivas, Karagellis, & Roe, 1985). An especially
compelling line of evidence is research that shows that, with practice and
feedback, women improve as much as men do on spatial tasks (e.g., Law, Pel-
legrino, & Hunt, 1993; see Halpern, 1992 for a review). Some cross-cultural
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