Jancke and Steinmetz further demonstrate the salience of the relationship between FBV and CC size when they divided subjects on the basis of FBV and then correlated measures of dichotic listening performance within the large- and the small-brained groups. Their results showed a different pattern of correlations for the two groups in a fashion similar to what other researchers have demonstrated when subdividing groups by sex and hand preference (Zaidel, Clarke, and Suyenobu, 1990). The results serve not only as further functional validation of the importance of FBV in CC size and function, but also emphasize the importance of the within-group comparison (Cowell et al., 1995).
In view of their proposal that FBV plays a major role in the determination of CC size, Jancke and Steinmetz explore the relationship between hand preference and regional CC anatomy. Their study measured hand preference using the Annett handedness questionnaire, and subjects were classified as either right-handers, mixed-handers, or left-handers. On the basis of this classification, there were no significant group differences. However, Cowell and colleagues (1993) showed that both direction and degree were salient dimensions of hand preference with respect to regional CC size (see
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