Complexity_ A Guided Tour - Melanie Mitchell [94]
FIGURE 13.1. Part of Copycat’s Slipnet. Each node is labeled with the concept it represents (e.g., A–Z, rightmost, successor). Some links between nodes (e.g., rightmost–leftmost) are connected to a label node giving the link’s relationship (e.g., opposite). Each node has a dynamic activation value (not shown) and spreads activation to neighboring nodes. Activation decays if not reinforced. Each link has an intrinsic resistance to slippage, which decreases when the label node is activated.
The Workspace: A working area in which the letters composing the analogy problem reside and in which perceptual structures are built on top of the letters.
Codelets: Agents that continually explore possibilities for perceptual structures to build in the Workspace, and, based on their findings, attempt to instantiate such structures. (The term codelet is meant to evoke the notion of a “small piece of code,” just as the later term applet in Java is meant to evoke the notion of a small application program.) Teams of codelets cooperate and compete to construct perceptual structures defining relationships between objects (e.g., “b is the successor of a in abc,” or “the two i’s in iijjkk form a group,” or “the b in abc corresponds to the group of j’s in iijjkk,” or “the c in abc corresponds to the k in kji ”). Each team considers a particular possibility for structuring part of the world, and the resources (codelet time) allocated to each team depends on the promise of the structure it is trying to build, as assessed dynamically as exploration proceeds. In this way, a parallel terraced scan of possibilities emerges as the teams of codelets, via competition and cooperation, gradually build up a hierarchy of structures that defines the program’s “understanding” of the situation with which it is faced.
Temperature, which measures the amount of perceptual organization in the system. As in the physical world, high temperature corresponds to disorganization, and low temperature corresponds to a high degree of organization. In Copycat, temperature both measures organization and feeds back to control the degree of randomness with which codelets make decisions. When the temperature is high, reflecting little perceptual organization and little information on which to base decisions, codelets make their decisions more randomly. As perceptual structures are built and more information is obtained about what concepts are relevant and how to structure the perception of objects and relationships in the world, the temperature decreases, reflecting the presence of more information to guide decisions, and codelets make their decisions more deterministically.
A Run of Copycat
The best way to describe how these different components interact in Copycat is to display graphics from an actual run of the program. These graphics are produced in real-time as the program runs. This section displays snapshots from a run of the program on abc ⇒ abd, mrrjjj ⇒ ?
Figure 13.2: The problem is presented. Displayed are: the Workspace (here, the as-yet unstructured letters of the analogy problem); a “thermometer” on the left that gives the current temperature (initially set at 100, its maximum value, reflecting the lack of any perceptual structures); and the