with this route or doorway between mental and real.” [6, p.354]. Such interactions between the described fields will be illustrated by some examples. Perspec-tive for example affects back to the designed object. The classical example of an arcaded courtyard in “Palazzo Spada” in Rome, de-signed by Francesco Borromini 1635 (Figure 10), is an architectural trompe-l'œil in which diminishing rows of columns and a rising floor create the optical illusion of a long gallery.