Guest editorial essay

With the invention of the stereoscope, Charles Wheatstone transformed not only our vision of pictures, but also our understanding of some intricacies of spatial perception. In his obituary notice in Nature, the following comments were made by Signor Volpicelli of the Academia dei Lincei: ``Our countryman, Leonardo da Vinci, in 1500, or thereabouts, conceived and was the first to affirm, that from a picture it was not possible to obtain the effect of relief. But Wheatstone, reflecting profoundly in 1838, on the physiology of vision, invented the catoptric stereoscope, with which he philosophically solved the problem of the optical and virtual production of relief '' (1876, page 502). Thus, the stereoscope could restore the dimension of depth missing in single pictures. But have many such paired paintings been produced by artists since Wheatstone's death? There certainly are some, and they represent tours de force on behalf of the artists, but they have not attracted much attention. Salvador Dali produced some large paired paintings in the 1970s. At about the same time an alternative technique was devised by the artist Ludwig Wilding (figure 1). Guest editorial essay Perception, 2007, volume 36, pages 479 ^ 482