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Ikuya Murakami, Yuya Seshita, Sohei Kito; The flash grab effect into the blind spot. Journal of Vision 2021;21(9):2344. doi: https://doi.org/10.1167/jov.21.9.2344.
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The flash grab effect refers to the phenomenon in which a flashed bar superimposed upon a moving pattern at its directional reversal appears to be shifted in the new direction, as if the flash is grabbed by the reversed object, which appears to have reversed well before the actual reversal (Cavanagh & Anstis, 2013). This effect is deemed to require attention and conceivably involve high-level localization mechanisms. If the high-level account is true, the mechanism should have access to positional representation that has already taken care of image imperfections stemming from the retinal structure, such as the blind spot. The blind spot is the region corresponding to the optic disk on the retina where no rods/cones exist, so some computation is required to enjoy a seamless visual world despite the lack of visual inputs there. This study examined whether the flash grab effect occurs for a flashed bar presented just outside the blind-spot border such that the bar is grabbed by a reversing pattern and dragged into the inside of the blind spot. In a control condition, the bar at the same location was flashed just when the moving pattern reversed its direction to grab the bar away from the blind spot. In further control conditions, the flash location was far away from the blind spot, or the flash onset time was far away from the directional reversal time of the moving pattern; when the flash onset did not coincide with it, another illusion called the flash drag effect was also expected to occur. In all conditions, we confirmed illusory position shifts in line with the flash grab, or drag, effect, thus we found an illusory position shift into the blind spot due to the flash grab effect. Our results support the claim of high level position processing requiring attention.
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