children, they may be expected to take something quite different from their experiences with that environment.

Given the likelihood of statistical and transaction interactions, it is difficult to tease apart the effects of nature and nurture. Two illustrations of an interactive approach follow. In the first, Casey (1996) hypothesized that girls with different brain organization patterns might be expected to respond differently to similar kinds of spatial experiences. She operationalized brain organization on the basis of handedness, which has been linked to different patterns of hemispheric dominance (Annett, 1985). She operationalized spatial experience as exposure to a math-science college curriculum, a curriculum that provides significant exposure to spatial thinking. Although Casey acknowledged that college major is not purely an environmental variable (students self-select into majors; hence those who self-select into math and science may be expected to have relatively strong spatial skills), the self-selection component was held constant because all participants had self-selected into the major. Hence, the critical question was whether there would be differential effects of exposure to that college curriculum as a function of brain organization (measured by handedness). Consistent with the interactive hypothesis, her data show that the same curriculum enhanced spatial performance (measured by a mental rotation task) differentially in relation to students’ handedness.

A second illustration comes from work by Berenbaum and colleagues (e.g., Berenbaum et al., 1995; Resnick et al., 1986). Although this work is often taken as a demonstration of direct effects of biology (hormones) on spatial outcomes, it simultaneously speaks to the manner in which biology and experience may interact. For example, CAH girls, subjected to unusually high androgen levels prenatally, show greater spatial skills than do their non-CAH relatives (Resnick et al., 1986). One possible interpretation is a direct effect of prenatal androgens (and hence brain organization) on spatial skills. However, another possibility is that there is only an indirect effect. Berenbaum has shown that CAH girls prefer toys and activities more typical of boys than of girls (Berenbaum and Hines, 1992; Berenbaum and Snyder, 1995). Perhaps these preferences are driven by atypically high activity levels that lead CAH girls to prefer objects and activities that allow active, rather than passive, play. Under this scenario, CAH girls’ gravitation toward “boys’” toys stems from the fact that these toys support more action or manipulation, rather than from the fact that they support spatial play in particular; however, playing with these toys provides experience conducive to developing higher-level spatial skills.

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