Abstract
Against the general notion of separate processing of colour and motion, recent studies have revealed various forms of colour influence on motion perception. On the other hand, it remains unknown how motion information contributes to colour perception. Last year, we reported “motion-induced colour mixture” (Nishida et al. VSS'04; Watanabe et al. ECVP'04), in which moving bars whose colour temporally alternates between two colours (e.g., red and green) at each jump is perceived to be in the mixed colour (yellow). This phenomenon suggests that the visual system may integrate colour signals presented at different locations on the retina, but along the trajectories of the same moving objects. However, an alternative interpretation is that motion signals simply lower the spatial resolution of the colour mechanisms. If colour signals are indeed integrated along motion trajectories, motion signals should also facilitate segregation of colours if they are presented at the same retinal locations, but along different motion trajectories. To test this, we asked the subjects to rate the magnitude of colour segregation/mixture for gratings in which red and green bars (6′ in width) spatially alternated with a constant dark interval (variable between 6′ and 66′). The grating shifted every 6.25 ms by 6′ in the orthogonal direction. This gave rise to an alternation of red and green at each retinal location. The alternation rate varied between 6.7 to 40 Hz depending on the inter-bar spacing. As the alternation rate was increased, the perceived colour gradually changed from red/green to yellow. We compared this function with that measured with a non-motion display where the same temporal pattern was seen as stationary chromatic flickers. As we expected, the rating of segregation of red/green was significantly higher in the motion display than in the non-motion display. This “motion-induced colour segregation” strongly supports colour integration along motion trajectory.