There is now persuasive evidence that the central nervous system in humans retains a significant degree of plasticity and remains responsive to experience throughout adulthood (Steven & Blakemore, 2004). Although this plasticity has primarily been documented for motor skills (Karni et al., 1995; Pascual-Leone et al., 1995), evidence for the modifying effect of experience on the structure or organization of cognitive processes has also been accumulating. For example, C. S. Green and Bavelier (2003) reported that individuals who play video games had faster response times on attention tasks and better visual processing than nonplayers who were otherwise comparable. In another example, Maguire et al. (2000) found that London taxi drivers with extensive training in route finding had enlarged portions of the hippocampi devoted to spatial processing. Gaser and Schlaug (2003) used voxel-based morphometry to compare professional musicians, amateur musicians, and nonmusicians; they found increased gray matter density for professional musicians with smaller increases for amateur musicians in regions of the motor, auditory, and visual cortex. They interpreted these results as evidence for use-dependent structural change and showed as well that the degree of change is calibrated to the degree of experience. Similarly, Mechelli et al. (2004) found increased density in gray and white matter in the left inferior parietal cortex of early bilinguals that corresponded to learning a second language, with greater density increases as proficiency in the second language increased.