Learning new lexical categories induced changes in gray matter in adult human brain

Abstract

The human brain has been shown to exhibit changes in the volume and density of gray matter as a result of training over periods of several weeks or longer. We show that these changes can be induced much faster by using a training method that is claimed to simulate the rapid learning of word meanings by children. Here, we use whole-brain magnetic resonance imaging (MRI) to measure subjects’ brain structure before and after earning newly defined and named subcategories of the universal categories green and blue. Gray matter density is found to increase in color regions of the left visual cortex after a short-term training (around 2 hours). This pattern of findings demonstrates structural plasticity of the human brain, specifically during the acquisition of new, named categories. Also, prior behavioral and neuroimaging research has shown that differences between languages in the boundaries of named color categories influence the categorical perception of color, as assessed by judgments of relative similarity, by response time in alternative forced-choice tasks, and by visual search. Moreover, further behavioral studies (visual search) and brain imaging studies have suggested strongly that the categorical effect of language on color processing is left-lateralized, i.e., mediated by activity in the left cerebral hemisphere in adults (hence “lateralized Whorfian” effects). The present results appear to provide a structural basis in the brain for the behavioral and neurophysiologically observed indices of these Whorfian effects on color processing.