A view of the apartment building ĪThe Futureā, located at 200 East 32nd Street in New York City. The balconies appear to tilt up, with tilt becoming more apparent the higher up the building one looks. (right) The same building, but viewed from the opposite side. The balconies now appear to tilt downwards.

The shape shown at left is constructed from a pair of identical semicircles, placed parallel to one another, one radius apart, and joined by a pair of parallel straight lines. In order to better view the effect at armās length, we suggest using a radius of 4 inches, and cutting the shape out of stiff card or some other rigid material. The stimulus is viewed monocularly, placed parallel to the ground and elevated above the line of sight. When the flat object is held at an elevation of 45”, it surprisingly acquires an upward curl when one eye is closed and stereo information removed. When the rigid object is moved up or down, it appears to flex and change shape, and be more or less curled as the elevation above eye level is increased or decreased.