Color vision

Among basic vision research, which aim to reveal higher levels of the human visual function, I review recent advances in color vision, focusing on color memory and categorical color perception research. It is known that color varies continuously in color space. At the same time, however, we recognize colors as categories: such as, red, green, yellow, and blue although there are obvious color differences among colors classified in the same category. Some previous research has shown that a uniform color space is consistently divided into basic categorical color regions. Previous memory studies report that color stored in memory is more strongly influenced by a color in the same category than one in a different category, and that a color becomes ambiguous in memory when restricted within a categorical region. We performed color memory and categorical color naming experiments to see how color memory and color categories were related in the higher color vision mechanisms. It was shown in these experiments that memory-matched colors distributed neither uniformly nor randomly in the OSA uniform color space, but they made several clusters in the color space. These clusters tended to coincide with the Berlin and Kay´s 11 basic color categories (1969), but some clusters divided the basic color category regions into several subcategories. These results indicate that color space in memory is not uniform, but has a categorical structure. It is suggested that there is some physiological mechanism for categorical color perception in a high level of color vision. This mechanism could yield psychophysical properties obtained in the categorical color naming and color memory experiments