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than our close friends [18]. This tendency leads to social networks organized
as densely knit clumps of small structures linked to other similar structures by
bridges between them. Granovetter called this type of bridges “weak ties”, and
demonstrated their importance in permitting the flow of resources, particularly
information, between otherwise unconnected clusters [17]. Embeddedness and
bridges express a network topology which exhibits small-world features [28].
Building on Granovetter's “strength of weak ties” theory [18], sociological re-
search on “small world” networks suggests that in a social network the presence
of bridges promotes cultural diffusion, homogeneity and integration, but only
under the assumption that relations hold a positive value [13]. This last concern
is a trademark of the social simulation stream which uses a non-reasoning ap-
proach to agent modeling. We will show that our model does not need such a
specification.
Following the experimental design by Flache & Macy [13], we use a “caveman
graph” to represent a situation where clusters are maximally dense. We use this
topology as a starting point to confront our results with a renown model in
literature. We then allow for two kind of structural settings:
-
a first one where each “cave”, i.e. each cluster of the graph, is disconnected
from the others, thus agents can interact within their own cluster only;
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a second one where a random number of bridges is added between caves,
thus agents can interact occasionally with members of different caves. Even
if our mechanism does not guarantee that all the caves become connected, on
average the resulting networks exhibit small-world network characteristics.
Such a network structure is imposed exogenously to agents and kept static once
generated. Random bridges play the role of weak links. By connecting previously
unconnected densely knit caves, they play the role that acquaintances play in
real life, and thus bridges are supposed to carry all the information beyond that
available in a single cave. However, we do not impose a positive or negative value
to links. Instead, links only represent the possibility of communication between
any two pair of agents. The bit of information transmitted may have a positive or
negative value, depending on the content exchanged: something that reinforces
agent opinions or that radically changes them.
We call the stream of information exchanged between two agent a “simulated
dialogue”. The dialogue mechanism represents the micro-level assumption that
governs our model and builds on Mercier & Sperber's work.
3 Agent Reasoning and Interaction
According to Mercier & Sperber's argumentative theory of reasoning [21], the
function of human reasoning is argumentative and its emergence is best under-
stood within the framework of the evolution of human communication. Reason-
ing developed as a “tool” to convince others by means of arguments exchanged
in dialogues. We report a brief summary of a communication process according
to Mercier & Sperber:
