Reading from Left to Right

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Science  12 Dec 2008:
Vol. 322, Issue 5908, pp. 1610-1611
DOI: 10.1126/science.322.5908.1610d

Categorical perception is a robust phenomenon and can be illustrated by the more rapid discrimination of two colors separated by a fixed chromatic distance when the colors fall on opposite sides of a category boundary, such as blue/green, than when they both lie within a single category. Both adults and infants exhibit this capacity, and Franklin et al. have investigated the influence of hemispheric lateralization and of language in a pair of studies. First, by presenting the colors in the left or right visual field (LVF or RVF), they show that adults react more quickly to RVF stimuli and hence that categorical perception of color is lateralized (in a relative, though not absolute, sense) to the left hemisphere, to which the RVF projects. Consistent with a left-hemispheric predominance of language skills, a verbal interference task blocked categorical perception in adults, whereas a visual interference task did not. Prelinguistic infants, on the other hand, displayed a right-hemispheric (LVF) superiority in the categorical perception of colors. Second, they recruited a group of toddlers 2 to 5 years of age and assessed their comprehension of the words blue and green. When tested on the same paired colors, the reaction times of these toddlers did not vary as a function of semantic knowledge, but those that had mastered the words demonstrated a hemispheric lateralization that was adult-like; that is, categorical perception for RVF stimuli. Toddlers who were still learning about blue and green retained the LVF pattern of categorical perception. — GJC

Proc. Natl. Acad. Sci. U.S.A. 105, 3221; 18221 (2008).

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