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

M/230 | HOW THE MIND WORKSthe computer make a copy for the right eye, but with one twist: heshifted a patch of dots a bit over to the left, and inserted a new stripe ofrandom dots into the gap at the right so the shifted patch would be perfectlycamouflaged. Each picture on its own looked like pepper. Butwhen put in the stereoscope, the patch levitated into the air.H1rIMany authorities on stereo vision at the time refused to believe itbecause the correspondence problem the brain had to solve was just toohard. They suspected that Julesz had somehow left little cut marksbehind in one of the pictures. But of course the computer did :no suchthing. Anyone who sees a random-dot stereogram is immediatiely convinced.All it took for Julesz' occasional collaborator, Christopher Tyler, toinvent the magic-eye autostereogram was to combine the wallpaperautostereogram with the random-dot stereogram. The computer generatesa vertical stripe of dots and lays copies of it side by side, creatingrandom-dot wallpaper. Say each stripe is ten dots wide, and woinumberthe dots from 1 to 10 (using "0" for 10):12345678901234567890i234567890123«67890123456789C1234S678 i 9C123456789C1234567B90123456789012345678901234567890123456789012345678901234567S901234567850123456789012345678901234567890—and so on. Any clump of dots—say, "5678"—repeats itself every tenspaces. When the eyes fixate on neighboring stripes, they falsely fuse,just as they do with a wallpaper stereogram, except that the brain issuperimposing stretches of random dots rather than flowers. Rememberthat in a wallpaper stereogram, copies of a pattern that have beensquashed closer together will float above the rest because their lines ofsight cross closer to the viewer. To make a patch float out of a rrtagic-eye