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

270 | HOW THE MIND WORKShave dents and wobbles and come in different styles and models. No twosuitcases have identical dimensions, and some have rounded or beefedupcorners and fat or skinny handles. So the representation of the shapeabout to be matched shouldn't be an exact mold of every hill and valley.It should be couched in forgiving categories like "slab" and "U-shapedthingy." The attachments, too, can't be specified to the millimeter buthave to allow for some slop: the handles of different cups are all "on theside," but they can be a bit higher or lower from cup to cup.The psychologist Irv Biederman has fleshed out Marr's two ideas withan inventory of simple geometric parts that he calls "geons" (by analogyto the protons and electrons making up atoms). Here are five geons alongwith some combinations:Biederman proposes twenty-four geons altogether, including a cone, amegaphone, a football, a tube, a cube, and a piece of elbow macaroni.(Technically, they are all just different kinds of cones. If an ice creamcone is the surface swept out by an expanding circle as its center ismoved along a line, geons are the surfaces swept out by other 2-D shapesas they expand or contract while moving along straight or curved lines.)Geons can be assembled into objects with a few attachment relationslike "above," "beside," "end to end," "end to off-center," and "parallel."These relations are defined in a frame of reference centered on theobject, of course, not the visual field; "above" means "above the maingeon," not "above the fovea." So the relations stay the same when theobject or viewer moves.Geons are combinatorial, like grammar. Obviously we don't describeshapes to ourselves in words, but geon assemblies are a kind of internallanguage, a dialect of mentalese. Elements from a fixed vocabulary arefitted together into larger structures, like words in a phrase or sentence.A sentence is not the sum of its words but depends on their syntacticarrangement; A man bites a dog is not the same as A dog bites a man.Likewise, an object is not the sum of its geons but depends on their spatialarrangement; a cylinder with an elbow on the side is a cup, while a