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Shin'ya Nishida, Junji Watanabe, Susumu Tachi, Ichiro Kuriki; Motion-induced colour mixture. Journal of Vision 2004;4(8):162. doi: 10.1167/4.8.162.
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We found that different colours presented at separate retinal locations were perceptually mixed when they were temporally integrated through rapid apparent motion. Our stimulus consisted of a stationary vertical red-green square-wave grating: each colour stripe subtended 6 min in width. It was seen only through an array of bar-shaped slits, each subtending 12 min in width, through which just one cycle of the grating was visible. At constant temporal intervals, the slits repetitively made a leftward (or rightward) jump of 6 min length. When the inter-jump-interval was very long, the observer could see retinally-veridical bicoloured bars. When the interval was short (<=12.5 ms), however, the observer saw yellow bars, even though the same retinal location was not stimulated by red and green. Similarly, bars uncovering yellow and blue stripes were seen as white when they were in motion. This is not an artefact caused by tracking eye movement, since the colour mixture simultaneously occurred in two slit arrays that moved only briefly (200 ms) in opposite directions. Moreover, eye position measurements confirmed that tracking eye movements did not occur during the stimulus presentation. One possible account of this phenomenon is that rapid stimulus changes lower the spatial resolution of colour mechanisms, as they do for luminance mechanisms. However, the colour mixture disappeared when the moving stimulus was further masked by the same, but stationary slit array, which preserved the pattern of local colour changes, but removed the perception of the bars' movement. This implies a tight relationship between this type of colour mixing and motion perception. Our findings suggest that the visual system attempts to integrate colour information across different samples in space and time that belong to the same moving object, as opposed to the general belief that colour mixture is an early-level phenomenon, and that colour processing is independent of motion processing.
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