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Rick H. Cai; Illusory conjunction between continuous and discrete changes in the absence of motion. Journal of Vision 2006;6(6):557. doi: https://doi.org/10.1167/6.6.557.
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Previously, we demonstrated an illusion in which a bar gradually changes its height as it moves, and somewhere along its trajectory, it also changes to a different color for one frame. The new color is assigned not only to a new spatial location, but also to a different sized bar (an illusory conjunction of color and shape). We proposed a model based on the principle that the brain represents continuous changes differently from abrupt changes, leading to an asynchrony in the processing of the two (Cai & Schlag, VSS, 01). Here we tested two predictions from the this model. First, according to the model, the illusion should not be limited to linear motion and height change. We used a hollow ring that expanded from the center. As the expanding ring reached a certain size, it changed to a different color for one frame. The new color was perceived as belonging to a ring of greater size. Second, we created a display in which dots were scattered randomly within a rectangular area. The density of the dots increased with time. There was no net motion energy within the rectangular area. As the density reached a certain level, all the dots changed color for one frame. The odd color was perceived as belonging to a field of dots of higher density then the actual case. This demonstrates that, consistent with the model prediction, illusory conjunction occurs between continuous and discrete changes, even if such changes involve no motion.
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