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

104 J HOW THE MIND WORKSWith this move, interesting things begin to happen. The networkbegins to resemble human thought processes in ways that sparsely connectednetworks do not. For this reason psychologists and artificial intelligenceresearchers have been using everything-connected-to-everythingnetworks to model many examples of simple pattern recognition. Theyhave built networks for the lines that co-occur in letters, the letters thatco-occur in words, the animal parts that co-occur in animals, and thepieces of furniture that co-occur in rooms. Often the decision node atthe top is thrown away and only the correlations among the propertiesare calculated. These networks, sometimes called auto-associators, havefive nifty features.First, an auto-associator is a reconstructive, content-addressable memory.In a commercial computer, the bits themselves are meaningless, andthe bytes made out of them have arbitrary addresses, like houses on astreet, which have nothing to do with their contents. Memory locationsare accessed by their addresses, and to determine whether a pattern hasbeen stored somewhere in memory you have to search them all (or useclever shortcuts). In a content-addressable memory, on the other hand,specifying an item automatically lights up any location in memory containinga copy of the item. Since an item is represented in an auto-associatorby turning on the units that represent its properties (in this casecelery, greenness, leafiness, and so on), and since those units are connectedto one another with strong weights, the activated units will reinforceone another, and after a few rounds in which activation reverberatesthrough the network, all the units pertaining to the item will lock into the"on" position. That indicates that the item has been recognized. In fact, asingle auto-associator can accommodate many sets of weights in its batteryof connections, not just one, so it can store many items at a time.Better yet, the connections are redundant enough that even if only afart of the pattern for an item is presented to the auto-associator, say,greenness and crunchiness alone, the rest of the pattern, leafiness, getscompleted automatically. In some ways this is reminiscent of the mind.We do not need predefined retrieval tags for items in memory; almostany aspect of an object can bring the entire object to mind. For example,we can recall "vegetable" upon thinking about things that are green andleafy or green and crunchy or leafy and crunchy. A visual example is ourability to complete a word from a few of its fragments. We do not see thisfigure as random line segments or even as an arbitrary sequence of letterslike MIHB, but as something more probable: