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

274 J HOW THE MIND WORKSeven cars) have some of these geometric features, the module will haveno choice but to analyze them, even if they are most useful for faces. Tocall a module a face-recognizer is not to say it can handle only faces; it isto say that it is optimized for the geometric features that distinguishfaces because the organism was selected in its evolutionary history for anability to recognize them.The geon theory is lovely, but is it true? Certainly not in its purest form,in which every object would get one description of its 3-D geometry,uncontaminated by the vagaries of vantage point. Most objects areopaque, with some surfaces obscuring others. That makes it literallyimpossible to arrive at the same description of the object from every vantagepoint. For example, you can't know what the back of a house lookslike when you are standing in front of it. Marr got around the problem byignoring surfaces altogether and analyzing animals' shapes as if they werebuilt out of pipe cleaners. Biederman's version concedes the problemand gives each object several geon models in the mental shape catalogue,one for each view required to reveal all its surfaces.But this concession opens the door to a completely different way ofdoing shape recognition. Why not go all the way and give each shape alarge number of memory files, one for every vantage point? Then the fileswouldn't need a fancy object-centered reference frame; they could usethe retinal coordinates available free in the 2 l h-D sketch, as long as therewere enough files to cover all the angles of view. For many years this ideawas dismissed out of hand. If the continuum of viewing angles werechopped into one-degree differences, one would need forty thousandfiles for every object to cover them all (and those are just to cover theviewing angles; they don't embrace the viewing positions at which theobject is not dead-center, or the different viewing distances). One cannotskimp by specifying a few views, like an architect's plan and elevation,because in principle any of the views might be crucial. (Simple proof:Imagine a shape consisting of a hollow sphere with a toy glued on theinside and a small hole drilled opposite it. Only by sighting the toyexactly through the hole can the entire shape be seen.) But recently theidea has made a comeback. By choosing views judiciously, and using apattern-associator neural network to interpolate between them when an