One of this year鈥檚 finalists was a shrinking and stretching bathtub. It鈥檚 an illusion that of the American University in Washington DC noticed whilst walking past a large billboard poster (see video). But how can walking past a picture of a bathtub make its dimensions change?
The effect occurs because we naturally perceive the tub in the poster as a 3D object, but the still image in the poster happened to be photographed from an oblique angle. This means that the tub鈥檚 orientation relative to the viewer changes depending on the viewing angle. So by walking from one end of the image to the other, the viewer experiences a series of different retinal images of the tub, which makes the tub look smaller from the right but larger from the left.
See more: Don鈥檛 believe your eyes: This year鈥檚 best illusions
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