Both adults and infants are faster at discriminating between two colors from different categories than two colors from the same category, even when between-and within-category chromatic separation sizes are equated. For adults, this categorical perception (CP) is lateralized; the category effect is stronger for the right visual field (RVF)-left hemisphere (LH) than the left visual field (LVF)-right hemisphere (RH). Converging evidence suggests that the LH bias in color CP in adults is caused by the influence of lexical color codes in the LH. The current study investigates whether prelinguistic color CP is also lateralized to the LH by testing 4-to 6-month-old infants. A colored target was shown on a differently colored background, and time to initiate an eye movement to the target was measured. Target background pairs were either from the same or different categories, but with equal target-background chromatic separations. Infants were faster at initiating an eye movement to targets on different-category than same-category backgrounds, but only for targets in the LVF-RH. In contrast, adults showed a greater category effect when targets were presented to the RVF-LH. These results suggest that whereas color CP is stronger in the LH than RH in adults, prelinguistic CP in infants is lateralized to the RH. The findings suggest that language-driven CP in adults may not build on prelinguistic CP, but that language instead imposes its categories on a LH that is not categorically prepartitioned.language and thought ͉ nature/nurture ͉ lateralization ͉ perceptual development C ategorical perception (CP) of color is shown when two colors that belong to different color categories (between-category judgments) are discriminated faster, or more accurately, than two colors belonging to the same color category (within-category judgments), even when between-and within-category chromatic separation sizes are equated (1). ʈ This effect is found in adults (2-5), children and toddlers (6, 7), and infants (8-10). The role of language in the effect has been extensively debated (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). For example, some have advanced the hypothesis that the on-line use of language is the origin of the effect: comparing stimulus labels aids discrimination for between-category pairs and/or hinders discrimination for within-category pairs. In support of this hypothesis, for adult participants, CP is found only if the category boundary is marked in the participant's language (3, 12, 13), and verbal interference eliminates CP, but visual interference does not (4,5,13,14). It has, however, been found that color CP occurs prelinguistically in toddlers and infants, who have no color language (6,(8)(9)(10).A recent set of studies looking at hemispheric asymmetries in color CP has added a new perspective on the debate. Gilbert et al. (14), using a visual search task, found that the time to detect a colored target among differently colored distractors was faster when target and distractors were from different categories (e.g., bl...

Adult colour preference has been summarized quantitatively in terms of weights on the two fundamental neural processes that underlie early colour encoding: the S-(L+M) ('blue-yellow') and L-M ('red-green') cone-opponent contrast channels (Ling, Hurlbert & Robinson, 2006; Hurlbert & Ling, 2007). Here, we investigate whether colour preference in 4-5-month-olds may be analysed in the same way. We recorded infants' eye-movements in response to pairwise presentations of eight colour stimuli varying only in hue. Infants looked longest at reddish and shortest at greenish hues. Analyses revealed that the L-M and S-(L+M) contrast between stimulus colour and background explained around half of the variation in infant preference across the hue spectrum. Unlike adult colour preference patterns, there was no evidence for sex differences in the weights on either of the cone-opponent contrast components. The findings provide a quantitative model of infant colour preference that summarizes variation in infant preference across hues.