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

220 HOW THE MIND WORKSThe late discovery of stereo vision is surprising, because it i& not hardto notice in everyday experience. Keep one eye closed for a few minutesas you walk around. The world is a flatter place, and you might find yourselfgrazing doorways and spooning sugar into your lap. Of course, theworld does not flatten completely. The brain still has the kinds of informationthat are present in pictures and television, like tapering, occlusion,placement on the ground, and gradients of texture. Most important,it has motion. As you move around, your vantage point changes continuously,making nearby objects whiz by and farther ones budge moreslowly. The brain interprets the flow pattern as a three-dimensionalworld going by. The perception of structure from optical flow is obviousin Star Trek, Star Wars, and popular computer screen-savers where whitedots fleeing the center of the monitor convey a vivid impression of flyingthrough space (though real stars would be too far away to give thatimpression to a real-life starfleet crew). All these monocular cues todepth allow people who are blind in one eye to get around pretty well,including the aviator Wiley Post and a wide receiver for the New YorkGiants football team in the 1970s. The brain is an opportunistic andmathematically adroit consumer of information, and perhaps that is whyits use of one cue, binocular disparity, eluded scientists for so long.Wheatstone proved that the mind turns trigonometry into consciousnesswhen he designed the first fully three-dimensional picture, thestereogram. The idea is simple. Capture a scene using two of Leonardo'swindows, or, more practically, two cameras, each positioned where oneeye would be. Place the right picture in front of a person's right eye andthe left picture in front of his left eye. If the brain assumes that the twoeyes look at one three-dimensional world, with differences in the viewscoming from binocular parallax, it should be fooled by the pictures andcombine them into a cyclopean image in which objects appear at differentdepths.left eye's picture right eye's picture