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

The Mind's Eye | 253costs, where cheap equals simple equals probable. In the parable, simpleoperations are easier to perform; in the visual system, simpler descriptionscorrespond to likelier arrangements in the world.Adelson and Pcntland have brought their parable to life by programminga computer simulation of vision that is designed to interpret sceneswith painted polygons much as we do. First, a shape analyzer (a softwareversion of the sheet-metal worker) strives for the most regular shape thatduplicates the image. Take the simple shape on the left in this diagram,which people see as a folded sheet, like a book held sideways.1The shape specialist tries to assemble a 3-D model of the input shape,shown on the right. When it begins, all it knows is that the corners andedges in the model have to line up with the dots and lines in the image; itdoes not know how far away they arc in depth. The model's vertices arebeads sliding on rods (like rays of projection), and the lines betweenthem are infinitely elastic strings. The specialist slides the beads arounduntil it arrives at a shape with the following desiderata. Each polygonmaking up the shape should be as regular as possible; that is, a polygon'sangles should not be too different. For example, if the polygon has foursides, the specialist strives for a rectangle. The polygon should be as planaras possible, as if the polygon is filled in with a plastic panel that ishard to bend. And the polygons should be as compact as possible, ratherthan elongated along the line of sight, as if the plastic panel is also hardto stretch.When the shape specialist is done, it passes on a rigid assembly ofwhile panels to the lighting specialist. The lighting specialist knowsthe laws that dictate how reflected light depends on the illumination, thelightness of the surface, and the angle of the surface. The specialist isallowed to move a single distant light source around to illuminate themodel from various directions. The optimal direction is the one thatmakes each pair of panels meeting at an edge look as much as possible