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

256 HOW THE MIND WORKSSEEING IN TWO AND A HALF DIMENSIONSOnce the experts have completed their work, what do they post on theblackboard that the rest of the brain accesses? If we could somehow showthe visual field from a rest-of-the-brains-eye view, like the hypotheticalcamera behind the eye of the Terminator, what would it look like? The veryquestion may sound like a thick-witted little-man-in-the-head fallacy, but itis not. It is about the information in one of the brain s data representationsand the form the information takes. Indeed, taking the question seriouslysends a bracing shock to our naive intuitions about the mind's eye.The experts in stereo, motion, contour, and shading have worked hardto recover the third dimension. It would be natural to use the fruits oftheir labors to build a three-dimensional representation of the world.The retinal mosaic in which the scene is depicted gives way to a mentalsandbox in which it is sculpted; the picture becomes a scale model. A 3-D model would correspond to our ultimate understanding of the world.When a child looms up to us and then shrinks away, we know we are notin Wonderland, where one pill makes you larger and one pill makes yousmall. And unlike the proverbial (and apocryphal) ostrich, w& do notthink that objects vanish when we look away or cover them up. We negotiatereality because our thought and action are guided by knowledge of alarge, stable, solid world. Perhaps vision gives us that knowledge in theform of a scale model.There is nothing inherently fishy about the scale-model theory. Manycomputer-aided design programs use software models of solid objects,and CAT-scan and MRI machines use sophisticated algorithms toassemble them. A 3-D model might have a list of the millions of coordinatesof the tiny cubes that make up a solid object, called volume elementsor "voxels" by analogy to the picture elements or "pixels" makingup a picture. Each coordinate-triplet is paired with a piece of information,such as the density of the tissue at that spot in the body. Of course,if the brain stored voxels, they would not have to be arranged in a 3-Dcube in the head, any more than voxels are arranged in a 3-D cube insidea computer. All that matters is that each voxel have a consistent set ofneurons dedicated to it, so the patterns of firing can register the contentsof the voxel.