Human Visual System Integrates Color Signals along a Motion Trajectory

Whether fundamental visual attributes, such as color, motion, and shape, are analyzed separately in specialized pathways has been one of the central questions of visual neuroscience [1–3]. Although recent studies have revealed various forms of cross-attribute interactions, including significant contributions of color signals to motion processing [4–9], it is still widely believed that color perception is relatively independent of motion processing. Here, we report a new color illusion, motion-induced color mixing, in which moving bars, the color of each of which alternates between two colors (e.g., red and green), are perceived as the mixed color (e.g., yellow) even though the two colors are never superimposed on the retina. The magnitude of color mixture is significantly stronger than that expected from direction-insensitive spatial integration of color signals [10, 11]. This illusion cannot be ascribed to optical image blurs, including those induced by chromatic aberration [12, 13], or to involuntary eye movements of the observer. Our findings indicate that color signals are integrated not only at the same retinal location, but also along a motion trajectory. It is possible that this neural mechanism helps us to see veridical colors for moving objects by reducing motion blur, as in the case of luminance-based pattern perception [14–19].