Emergence and separation of color categories: an NIRS study in prelingual infants and a k-means analysis on Japanese color-naming data

Two studies are introduced to discuss how color categories are established and separated. In the first study, the neural representations of color category in prelingual infants were studied with near-infrared spectroscopy (NIRS) technique. While the NIRS signals in the occipito-temporal area showed increased response to alternations of colors across categories but not for color changes within a category, no difference between these category conditions was observed in the occipital area. The second study demonstrated that the separation of basic color categories is an on-going event. The separation of color category from one blue category to two (light-blue and dark-blue) blue categories was tested, after the k-means clustering analysis was applied to the color-naming data of modern Japanese speakers. Surprisingly, it showed significant progress in the reduction of overlaps between the two blue categories, in comparison to a previous study on Japanese in 30 years ago. Together with other supporting evidences, including studies in non-human primates, the neural basis of the emergence and separation of color categories will be discussed.