Cortical response to categorical color perception in infants investigated by near-infrared spectroscopy

Significance There has been much debate on the Sapir–Wharf hypothesis regarding whether language affects our perceptual world. Despite much research on this topic, there remains no clear consensus on whether and how language affects categorical color perception. Here, we provide the first evidence, to our knowledge, that categorical color perception has a universal starting point prior to language acquisition. We measured the neural correlates of categorical color perception in prelinguistic infants. We found increased brain activities to colors in different categories, but not to colors in the same category. These results indicated that different color categories are differently represented in the visual cortex of prelinguistic infants, which implies that color categories may develop in the visual system before language acquisition. Perceptual color space is continuous; however, we tend to divide it into only a small number of categories. It is unclear whether categorical color perception is obtained solely through the development of the visual system or whether it is affected by language acquisition. To address this issue, we recruited prelinguistic infants (5- to 7-mo-olds) to measure changes in brain activity in relation to categorical color differences by using near-infrared spectroscopy (NIRS). We presented two sets of geometric figures to infants: One set altered in color between green and blue, and the other set altered between two different shades of green. We found a significant increase in hemodynamic responses during the between-category alternations, but not during the within-category alternations. These differences in hemodynamic response based on categorical relationship were observed only in the bilateral occipitotemporal regions, and not in the occipital region. We confirmed that categorical color differences yield behavioral differences in infants. We also observed comparable hemodynamic responses to categorical color differences in adults. The present study provided the first evidence, to our knowledge, that colors of different categories are represented differently in the visual cortex of prelinguistic infants, which implies that color categories may develop independently before language acquisition.