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

The Mind's Eye 269But suppose that instead of using the retinal reference frame, yourmemory file uses a frame aligned with the object itself. Your memorywould be "a rectangular slab with a handle parallel to the edge of the slab,at the top of the slab." The "of the slab" part means that you rememberthe positions of the parts relative to the object itself, not relative to thevisual field. Then, when you see an unidentified object, your visual systemwould automatically align a 3-D reference frame on it, just as it didwith Attneave's chorus line of squares and triangles. Now when youmatch what you see with what you remember, the two coincide, regardlessof how the suitcase is oriented. You recognize your luggage.That, in a nutshell, is how Marr explained shape recognition. The keyidea is that a shape memory is not a copy of the 272-D sketch but ratheris stored in a format that differs from it in two ways. First, the coordinatesystem is centered on the object—not, as in the 2V2-D sketch, on theviewer. To recognize an object, the brain aligns a reference frame on itsaxes of elongation and symmetry and measures the positions and anglesof the parts in that reference frame. Only then are vision and memorymatched. The second difference is that the matcher does not comparevision and memory pixel by pixel, as if placing a jigsaw puzzle piece in agap. If it did, shapes that ought to match still might not. Real objects