make an image appear out of nowhere: stare at a picture for a long time then look at a white surface, and you鈥檒l see an after-image before your eyes in its complementary colours. But now from Dartmouth College in Hanover, New Jersey, has come up with a twist on this visual trick.
He created an image by criss-crossing two rectangles with different-coloured stripes. After looking at the pattern for about a minute, you鈥檙e asked to stare at the empty outline of the two shapes. Focussing on either the horizontal or the vertical rectangle determines the after-image that you see.
Such 鈥済host鈥� images are caused by overstimulation of the eye鈥檚 photoreceptors, but the new illusion shows that shifting your attention can affect what appears as well.
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