Complexity_ A Guided Tour - Melanie Mitchell [95]
FIGURE 13.2.
FIGURE 13.3.
Figure 13.3: Thirty codelets have run and have investigated a variety of possible structures. Conceptually, codelets can be thought of as antlike agents, each one probabilistically following a path to explore but being guided by the paths laid down by other codelets. In this case the “paths” correspond to candidate perceptual structures. Candidate structures are proposed by codelets looking around at random for plausible descriptions, relationships, and groupings within strings, and correspondences between strings. A proposed structure becomes stronger as more and more codelets consider it and find it worthwhile. After a certain threshold of strength, the structure is considered to be “built” and can then influence subsequent structure building.
In figure 13.3, dotted lines and arcs represent structures in early stages of consideration; dashed lines and arcs represent structures in more serious stages of consideration; finally, solid lines and arcs represent structures that have been built. The speed at which proposed structures are considered depends on codelets’ assessments of the promise of the structure. For example, the codelet that proposed the a–m correspondence rated it as highly promising because both objects are leftmost in their respective strings: identity relationships such as leftmost ⇒ leftmost are always strong. The codelet that proposed the a–j correspondence rated it much more weakly, since the mapping it is based on, leftmost ⇒ rightmost, is much weaker, especially given that opposite is not currently active. Thus the a–m correspondence is likely to be investigated more quickly than the less plausible a–j correspondence.
The temperature has gone down from 100 to 94 in response to the single built structure, the “sameness” link between the rightmost two j’s in mrrjjj. This sameness link activated the node same in the Slipnet (not shown), which creates focused pressure in the form of specifically targeted codelets to look for instances of sameness elsewhere.
FIGURE 13.4.
Figure 13.4: Ninety-six codelets have run. The successorship fabric of abc has been built. Note that the proposed c-to-b predecessor link of figure 13.3 has been out-competed by a successor link. The two successor links in abc support each other: each is viewed as stronger due to the presence of the other, making rival predecessor links much less likely to destroy the successor links.
Two rival groups based on successorship links between letters are being considered: bc and abc (a whole-string group). These are represented by dotted or dashed rectangles around the letters in figure 13.4. Although bc got off to an early lead (it is dashed while the latter is only dotted), the group abc covers more objects in the string. This makes it stronger than bc—codelets will likely get around to testing it more quickly and will be more likely to build it than to build bc. A strong group, jjj, based on sameness is being considered in the bottom string.
Exploration of the crosswise a–j correspondence (dotted line in figure 13.3) has been aborted, since codelets that further investigated it found it too weak to be built. A c–j correspondence has been built (jagged vertical line); the mapping on which it is based (namely, both letters are rightmost in their respective strings) is given beneath it.
Since successor and sameness links have been built, along with an identity mapping (rightmost ⇒ rightmost), these nodes are highly active in the Slipnet and are creating focused pressure in the form of codelets to search explicitly for other instances of these concepts. For example, an identity mapping between the two leftmost letters is being considered.
FIGURE 13.5.
In response to the structures that have been built, the temperature has decreased to 76. The lower the temperature, the less random are the decisions made by codelets, so unlikely structures such as the bc group are even more unlikely to be built.
Figure 13.5: The abc and jjj groups have been