ABSTRACT
Under certain conditions. stationary, three-dimensional objects appear to move when an observer moves past them. Gregory (1970) reported. “When the inside of a mask appears as a normal face, it will swing to follow a moving observer …” (p. 128). and the same effect is seen when a three-dimensional wire cube appears to be reversed. (The hollow mask and moving cube illusion both appear at the exhibit “Seeing the Light” at the IBM Exploratorium in San Francisco and the New York Hall of Science in Flushing Meadows, NY.) This phenomenon depends on an apparent reversal of distance cues in a three-dimensional object, which gives rise to a paradoxical reversal in motion parallax cues. Normally, points closer to an observer appear to move more than points farther away when an observer moves. Reversing this relationship produces a robust illusion of movement.
