Socialization Effects on Spatial Ability
Several types of evidence suggest that spatial abilities are influenced by social experiences. Sex differences in spatial ability have been seen to depend on socioeconomic status (SES), with differences apparent in children from middle and high SES backgrounds, but not in children from low SES backgrounds (Levine, Vasilyeva, Lourenco, Newcombe, & Huttenlocher, 2005
). SES effects were suggested to result in part from access to experiences that facilitate spatial ability.
The experiences most often suggested to contribute to spatial ability include play with boys’ toys (e.g., construction sets, videogames) and engagement in boy-typed activities (e.g., sports) that encourage manipulation and exploration of the environment (e.g., Baenninger & Newcombe, 1989
; Connor & Serbin, 1977
). The link between spatial ability and aspects of sex-typed activities is weak-to-moderate (e.g., Newcombe, Bandura, & Taylor, 1983
), with some variability and inconsistency that likely reflects methodological and conceptual issues (Baenninger & Newcombe, 1989
; Voyer, Nolan, & Voyer, 2000
). Nevertheless, correlations are not evidence of causation: engagement in boy-typed activities might enhance spatial ability or instead reflect that ability, that is, children with high spatial ability might be attracted to toys that allow manipulation and exploration, or a third factor (such as early hormones or gendered socialization) may influence both of them. Some longitudinal data suggest that the causal path is from abilities to activities rather than the reverse (Newcombe & Dubas, 1992
It is, therefore, important to note direct experimental evidence that spatial ability can be enhanced by experience. In particular, spatial ability can be improved through practice and training, with generalization beyond training stimuli. For example, playing an action video game was seen to improve both spatial attention and mental rotation ability (Feng, Spence, & Pratt, 2007
). Training benefits both sexes, with women sometimes benefiting more than men, so that training may eliminate a sex difference (Lawton, 2010
Finally, stereotypes that emphasize women’s cognitive inferiority appear to impair their performance. This has been demonstrated in experimental studies of both math and spatial abilities, in which test-taking conditions are manipulated to emphasize or de-emphasize cognitive sex differences and their malleability. Women who were told that sex differences in math have genetic causes performed worse on math tests than those who were told that the differences have experiential causes (Dar-Nimrod & Heine, 2006
). Women who were told that men outperform women on spatial tasks performed worse on a mental rotations test than women who received neutral information, and the poorer performance of the group given negative stereotypes appeared to reflect increased emotional load (Wraga, Helt, Jacobs, & Sullivan, 2007
). The effect of stereotype information on spatial sex differences has also been seen in judgments of line orientation (Campbell & Collaer, 2009
Sex Hormone Influences on Spatial Ability
There is also considerable work on sex hormone effects on spatial ability, as also discussed in other papers in this special section. Most studies concern effects of circulating levels of testosterone and estradiol, although there is some evidence about early hormones, particularly androgens.
Evidence on cognitive effects of circulating sex hormones (activational effects) comes from studies of natural variations in hormones across individuals and within individuals (e.g., in association with the menstrual cycle) and effects of hormone replacement (in association with aging or surgical removal of the ovaries). Findings are complex (for reviews, see Hampson, 2007
; Maki & Sundermann, 2009
), but generally suggest that spatial ability is facilitated by testosterone in the moderate range (levels that are high for females and low for males) and verbal memory is facilitated by estradiol, especially in young postmenopausal women. Nevertheless, correlations between cognition and hormones may be difficult to interpret (e.g., circulating hormones may actually reflect prenatal hormones) and are not always found (e.g., Puts et al., 2010
), probably due to both methodological factors (e.g., statistical power, variations in tests used), and factors that modify the effects of both hormones (e.g., diet) and cognition (e.g., experiences). It is important to note that studies with even relatively large samples do not have sufficient power to see what are likely to be small effects. For example, even with 170 participants, power is still less than .80 to see a correlation as large as .2 with a two-tailed Type I error of .05; power is further reduced when several measures are examined.
Less is known about cognitive effects of hormones during early development (organizational effects). Evidence from rodents shows that high levels of early sex hormones enhance spatial performance in females (Williams & Meck, 1991
). The one study in nonhuman primates (Herman & Wallen, 2007
) is not straightforward because the spatial task used (attending to and using landmarks to solve spatial problems) showed a female superiority. Nevertheless, the sex difference appears to be influenced by prenatal androgens: blocking androgen exposure in males (through flutamide administration to pregnant rhesus monkey mothers) improved one aspect of their performance.
Human work linking prenatal hormones to later cognitive abilities is not entirely consistent. There are several types of human studies, focusing on (a) abilities in individuals with disorders of sex development (DSDs), in which prenatal and/or neonatal hormone levels are sex-atypical in the presence of sex-typical rearing and gender identity, (b) links between prenatal amniotic hormones and later abilities, (c) abilities in relation to inferred hormone exposure, determined by somatic markers (such as digit ratio) or having an opposite-sex twin.
Most studies of DSDs involve girls and women with congenital adrenal hyperplasia (CAH), who are exposed to higher than normal (sex-atypical) androgen levels during early development but who are reared and identify as female. Females with CAH have been found to have higher spatial ability than their sisters in childhood, adolescence, and adulthood (Hampson, Rovet, & Altmann, 1998
; Hines, Fane, et al., 2003
; Mueller et al., 2008
; Resnick, Berenbaum, Gottesman, & Bouchard, 1986
), with a meta-analysis suggesting that the effect is small to moderate (Puts, McDaniel, Jordan, & Breedlove, 2008
). But, females with CAH are not always seen to have enhanced spatial ability (Hines, Fane, et al., 2003
; Malouf, Migeon, Carson, Petrucci, & Wisniewski, 2006
; for review of other studies, see Berenbaum, 2001
). Evidence is more consistent in showing females with CAH to be masculinized in other sex-typed characteristics, most prominently activity interests but also sexual orientation and personal-social attributes such as aggression and interest in babies (for reviews, see Blakemore et al., 2009
; Hines, 2010
Males with CAH have also been studied for comparison. Most studies in nonhuman animals show that excess androgens in males have inconsistent effects, sometimes further masculinizing, sometimes demasculinizing, and most often having no effects (reviewed in Becker, Breedlove, Crews, & McCarthy, 2002
; Goy & McEwen, 1980
). Males with CAH have been found to be similar to unaffected males (usually their brothers) in most ways, including sex-typed activity interests and personal-social attributes (reviewed in Blakemore et al., 2009
). In contrast, males with CAH have been seen to have lower spatial ability than unaffected males (Hampson et al., 1998
; Hines, Fane, et al., 2003
); it is unclear whether such effects reflect androgens or complications from the disease that are more common in males than in females.
There are several methodological explanations for inconsistencies regarding spatial ability differences between females with and without CAH. The effect is not large, and most studies are underpowered; even with 50 participants per group (which is more than was used in any study), power is sufficient to detect a moderate difference at best. Tests used do not always show large sex differences in typical samples, further reducing power. Comparisons are often made to unrelated individuals, failing to provide sufficient matching on important background factors; in fact, in some studies, there were differences between females with and without CAH on IQ or on measures that do not show sex differences, confounding interpretation of spatial scores (for specific details and discussion, see Berenbaum, 2001
). Some samples were heterogeneous in age, which is related to spatial ability in nonlinear ways: Sex differences in spatial ability can be difficult to detect before mid-adolescence unless special tests are used; spatial ability declines with age beginning in early adulthood. Further, given demonstrated social influences on spatial ability, it is possible that social moderators reduced effects, making it difficult to detect differences between females with and without CAH in small samples.
Some inconsistencies may also reflect complexities of androgen effects on cognitive abilities. Studies in other species, including primates, indicate that there are multiple sensitive periods for behavioral effects of hormones, even during early development (e.g., Goy, Bercovitch, & McBrair, 1988
). If this happens in people, androgen may continue to have organizational effects into the neonatal period and perhaps beyond; this would result in spatial enhancement only in those females with CAH whose disease was not diagnosed or well-controlled immediately after birth.
In understanding the failures to find spatial enhancements in females with CAH, it is crucial to note that females with CAH have not been found to have significantly lower spatial ability than unaffected females. Such a difference would occur on occasion if there is truly no population difference between females with and without CAH.
Confirming evidence for early androgen effects on spatial ability comes from several other sources. The first concerns the counterpart of CAH: males with very low androgen levels reared as and identifying as males. Males with low early androgen levels due to idiopathic hypogonadotropic hypogonadism (IHH) were found to have lower spatial ability than controls (Hier & Crowley, 1982
), although there has been a failure to replicate (Cappa et al., 1988
); inconsistencies likely reflect low power with small samples. The second piece of converging evidence comes from the only published study of spatial ability in relation to amniotic hormones (Grimshaw, Sitarenios, & Finegan, 1995
). Seven-year-old girls who had high levels of amniotic testosterone had better spatial ability than girls who had low levels. But this result is complicated by the fact that the difference was not found on accuracy, and was seen only on a measure of speed of rotation and only in girls who showed evidence of using a mental rotation strategy.
The third source of converging evidence for androgen effects on spatial ability comes from individuals with an opposite-sex twin, in which prenatal hormone levels are inferred. This experiment is based on studies in nonhuman animals showing that behavior and physiology are influenced by naturally occurring variations in hormones that result from an animal’s position in the uterus, particularly the sex of its littermates (Ryan & Vandenbergh, 2002
). In particular, female rodents that develop between two males are less sex-typed than those that develop between two females. In three studies of human opposite-sex twins, females with a male co-twin were found to have higher spatial ability than females with a female co-twin (Cole-Harding, Morstad, & Wilson, 1988
; Heil, Kavsek, Rolke, Beste, & Jansen, 2011
; Vuoksimaa et al., 2010
). But, prenatal hormone influences are confounded with postnatal socialization in these findings; females with a male co-twin are reared with a male sibling of the same age. Evidence against socialization effects comes from women with slightly older siblings: those with a brother did not have better spatial ability than those with a sister (Heil et al., 2011
Finally, there are other studies of inferred hormones that focus on somatic biomarkers. The most widely studied marker is the ratio of the second to the fourth finger (digit ratio, 2D:4D) which shows a sex difference. Digit ratio is related to effective prenatal androgen exposure, but the link is relatively modest, making it a very weak marker of individual differences in prenatal androgens (Berenbaum, Bryk, Nowak, Quigley, & Moffat, 2009
). It is therefore difficult to know how to interpret data indicating that 2D:4D is generally not related to spatial ability (Puts et al., 2008
Thus, evidence from multiple sources converges to suggest that spatial ability is influenced by early androgen exposure. Evidence that sex differences in spatial ability appear very early in life (3–5 months of age) (Moore & Johnson, 2008
; Quinn & Liben, 2008
) is also consistent with (although does not prove) the importance of early hormones. Nevertheless, the evidence is less compelling than that for androgen effects on other sex-typed characteristics, especially activity interests and sexual orientation (for reviews, see Berenbaum & Beltz, 2011
; Blakemore et al., 2009
; Hines, 2010
) and conclusions about early androgen effects on spatial ability are sometimes dismissed because of the inconsistencies (Hines, 2010
; Hines, Fane, et al., 2003
; Valla & Ceci, 2011
). Furthermore, most studies have used a limited group of spatial tests (focused on two- and three-dimensional mental rotations), and none have considered “real-world” abilities that show large sex differences, including geographical knowledge and mechanical knowledge.
It is also important to consider the psychological mechanisms whereby early hormones influence spatial ability, particularly whether early androgens influence ability through their effects on childhood activities. Compelling evidence indicates that prenatal androgens increase interest in male-typed activities. Girls and women with CAH are more interested in and engaged with such activities than are unaffected females (including unaffected sisters). The differences are large, seen across the age range (childhood, adolescence, and adulthood), and found in studies using different measures and conducted in diverse countries (for reviews, see Blakemore et al., 2009
; Hines, 2010
). Converging evidence comes from other DSDs (reviewed in Blakemore et al., 2009
) and from a recent study of typical children, in which testosterone in amniotic fluid was found to be positively associated with childhood interest in boy-typical toys and activities (Auyeung et al., 2009
). But, it is currently unknown whether sex-typed activities mediate the effects of early androgens on spatial ability.