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Ryota Kanai, Frans A. J. Verstraten; Flash-Induced Palinopsia in normal observers: Perceiving the veridical and extrapolated positions simultaneously. Journal of Vision 2004;4(8):70. doi: 10.1167/4.8.70.
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© ARVO (1962-2015); The Authors (2016-present)
Palinopsia is a perceptual distortion where a visual image persists after removal of the stimulus. Observers (often patients) perceive the image of an object multiple times. Here, we report a novel illusion in which normal observers see a single moving object at two separate locations. We call this illusion Flash-Induced Palinopsia (FIP). The basic stimulus consists of a moving red solid disk and a ring-shaped flash (white) presented on a black background. Spatially, the inner edge of the flash overlaps with the disk's edge. When the disk moves, a flash is presented at the exact location where the disk is passing. This is similar to stimulus configurations that are typically used for flash-lag effect phenomena. Due to the flash-lag effect, the red moving disk is perceived as leading the flash. However, the region inside the ring is also perceived as red. This means that two red disks are perceived at the same time; one at the illusory location in front of the flash, and the other at the veridical position within the ring. In another configuration a hollow frame was flashed on the center part of a long moving vertical bar. The part of the bar that falls within the frame is perceived as lagging behind the parts of the bar that are outside the frame. As is true for our first stimulus, the veridical position of the inner part of the moving object — which is not usually perceived — can be revealed by presenting a transient stimulus. In additional experiments, we show that this FIP effect can be abolished when there is a small gap between the flash and the moving object, suggesting the involvement of a color filling-in process.
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