The Cube Illusion Interior corners were photocopied and folded with the spots in. Small cubes were cut and folded with the spots out. The folded sets were distributed - one set per person. Holding the interior corner with the arrow vertical and staring into the corner with one eye soon produced the illusion of looking at a solid cube. Rotating the wrist gave the illusion of the cube rotating in the opposite direction. Note: no explanation was offered. Scientists live with unanswered questions: teachers need to get used to that idea. A small cube, folded with the spots out, was then placed in the corner and the looking with one eye repeated. They saw a large cube with a small one apparently standing out on the front top corner. Rotating the wrist gave the illusion of rotation and counter rotation! Note 1: the large interior corner is seen inverted to appear as a cube. The small cube is seen as it really is - as a cube. The two figures are differently interpreted at the same time. Note 2: it is possible with a little practice to see both figures inverted. In this case there is a box cut out of the top front corner of the large cube. The figure is ambiguous in a three dimensional way. Many extensions are possible. For instance; the small central cube can be photocopied on to clear acetate. The figure is then ambiguous in very interesting way. More cubes can be added and nested. Extensions were not discussed with the group because the water was now hot and we were ready for the next stroke.

Thai teachers at an 'inservice' by Dr Ian   Be patient: it takes some people10 to 20 seconds to see it.