Béla Julesz, who lives in the USA, is one of the most famous living scientists of vision research. In 1960 he revealed the fact that the small differences of the retinal images of our eyes were enough to allow the perception of depth. Earlier it was believed that the processing of forms, shadows, textures and overlayings precedes the formation of stereoscopic pictures. Julesz made a striking counter-example by creating a stereogram from a chance mass of points, showing that without any forms, shadows, textures nor overlays, the hidden motif could be clearly perceived in depth.

His stereogram on a two-dimensional card shows a "real" three-dimensional illusion. Some examples can be found here, here, and here. However, the difference between the two retinal images is not the only way to provide depth perception. Let’s have a look at a few paintings as examples.

Symmetry plays an important role both in modern physics and in art history. The "naked" stereogram shows translational symmetry ; dilational symmetry is characteristic of fractals. We find it pleasing if the symmetry is not quite perfect. In this case, a stereoscopic pattern appears, and this similarly occurs in the case of the fractals.