Steven Pinker -- How the Mind Works - Hampshire High Italian ...

226 J HOW THE MIND WORKSBrewster also noticed that any irregularity in the spacing of a pair ofcopies makes them protrude or recess from the rest. Imagine that theflowers pierced by the lines of sight in the diagram are printed a bitcloser to each other. The lines of sight are brought together aind crosseach other closer to the eyes. The images on the retina will splay out tothe temples, and the brain sees the imaginary flower as being nearer.Similarly, if the flowers had been printed a bit farther apart, the lines ofsight will cross farther away, and their retinal projections will crowdtoward the nose. The brain hallucinates the ghost object at a slightlygreater distance.We have now arrived at a simple kind of "magic eye" illusion, the wallpaperautostereogram. Some of the stereograms in the books and greetingcards show rows of repeating figures—trees, clouds, mountains,people. When you view the stereogram, each tier of objects drifts in orout and lands at its own depth (although in these autostereograms,unlike the squiggly ones, no new shape emerges; we'll come to thosesoon). Here is an example, designed by Ilavenil Subbiah.It is like Brewster's wallpaper, but with the unequal separations put indeliberately rather than by a paperhanger's sloppiness. The pictureaccommodates seven sailboats because they are closely packed, but onlyfive arches because they are spaced farther apart. When you look behindthe picture, the sailboats seem closer than the arches because their misbuttonedlines of sight meet in a nearer plane.If you don't already know how to fuse stereograms, try holding thebook right up to your eyes. It is too close to focus; just let your eyes pointstraight ahead, seeing double. Slowly move the book away while keepingyour eyes relaxed and "looking through" the book to an imaginary point