This illusion is based on a billboard showing a bathtub shot at an angle. As we walk from one end of the picture to the other, the bathtub seems to stretch and shrink. Why? Each change in location results in a different retinal image. When processed in the usual way, each of these images results in a different 3D percept. Walking past the real bathtub will also produce a series of retinal images, different from those produced by the picture. All of these images will elicit a single, common 3D interpretation, and thus shape constancy.
VN:F [1.9.22_1171]Stretching out in the tub,