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

106 | HOW THE MIND WORKSbecause send a pen is the only guess that does not violate soime constraint.Sinned and pin would give me sinned a pin, which violates therules of grammar and plausible meaning; send and pin can be ruled outby the constraint that the two vowels were pronounced identically;sinned and pen can be ruled out because they violate both these constraints.This kind of reasoning takes a long time if all the compatibilities mustbe tested one at a time. But in an auto-associator, they are coded beforehandin the connections, and the network can evaluate them all at once.Suppose each interpretation is a toy neuron, one for sinned, one for send,and so on. Suppose that pairs of units whose interpretations are consistentare connected with positive weights and pairs of units whoseinterpretations are inconsistent are connected with negative weights.Activation will ricochet around the network, and if all goes well, it willsettle into a state in which the greatest number of mutually consistentinterpretations are active. A good metaphor is a soap bubble that wobblesin eggy and amoeboid shapes as the tugs among its neighboring moleculespull it into a sphere.Sometimes a constraint network can have mutually inconsistent butequally stable states. That captures the phenomenon of global ambiguity,in which an entire object, not just its parts, can be interpreted in twoways. If you stare at the drawing of a cube on page 107 (called a Neckercube), your perception will flip from a downward view of its top face toan upward view of its bottom face. When the global flip occurs, theinterpretations of all of the local parts are dragged with it. Every nearedge becomes a far edge, every convex corner becomes a concave corner,and so on. Or vice versa: if you try to see a convex corner as concave,you can sometimes nudge the whole cube into flipping. Thedynamics can be captured in a network, shown below the Cube, inwhich the units represent the interpretations of the parts, and the interpretationsthat are consistent in a 3-D object excite each other whilethe ones that are inconsistent inhibit each other.A fourth advantage comes from a network's ability to generalize automatically.If we had connected our letter-detector (which funneled abank of input units into a decision unit) to our letter-printer (which hadan intention unit fanning out into a bank of output units), we would havemade a simple read-write or lookup demon—for example, one thatresponds to a B by printing a C. But interesting things happen if you skipthe middleman and connect the input units directly to the output units.