From: LARRY KLAES (ljk4_at_msn.com)
Date: Fri Feb 14 2003 - 08:30:19 PST
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From: cunews_at_cornell.edu
Sent: Friday, February 14, 2003 10:10 AM
To: CUNEWS-SOCIAL_SCIENCE-L_at_cornell.edu; CUNEWS-SCIENCE-L_at_cornell.edu
Subject: Cornell News: Agent-based modeling
Artificial worlds used to unlock secrets of real human interaction
EMBARGOED UNTIL FRIDAY, FEB. 14, 2003, AT 10:30 A.M. EST
Contact: Roger Segelken
Office: 607-255-9736
E-mail: hrs2_at_cornell.edu
E-mail: deb27_at_cornell.edu
DENVER -- What do flocks of birds, traffic jams, fads, drinking
games, forest fires and residential segregation have in common? The
answer could come from a new computational research method called
agent-based modeling.
Michael Macy, a sociologist at Cornell University, Ithaca, N.Y., is
using this powerful new tool to look for elementary principles of
self-organization that might shed new light on long-standing puzzles
about how humans interact. A professor and chair of Cornell's
Department of Sociology, Macy will speak Feb. 14 at the annual
meeting of the American Association for the Advancement of Science in
Denver in a symposium, "Artificial Agent Societies: A Computational
Future for the Social Sciences."
The Cornell sociologist begins his lecture with a flock of
computer-generated birds wheeling synchronously through aerobatic
maneuvers. He credits Craig Reynolds, a pioneer of agent modeling and
three-dimensional computer animation, for the 1987 discovery that the
complex choreography of a flock requires that each bird (or "boid,"
as Reynolds called them) follow just three simple rules: head toward
the center of your neighbors, match their speed and trajectory and
avoid collisions. "Reynolds didn't model the flock as a unitary
collective nor did he model isolated birds; he modeled their
interactions at the relational level," Macy says. "That's agent-based
modeling."
Traditionally, sociologists have tried to understand social life as a
structured system of institutions and norms that shape individual
behavior from the top down, Macy notes. In contrast, agent modelers
suspect that much of social life emerges from the bottom up, more
like improvisational jazz than a symphony. For example, many
sociologists have attributed residential segregation to the
deliberate policies of banks, realtors and public officials
responding to popular prejudice. Yet 30 years ago, game theorist
Thomas Schelling used one of the first agent-based models to show how
extreme segregation tends to emerge even in populations that prefer
ethnic diversity, and in the absence of any institutional pressures.
Schelling's model was written long before the invention of the
personal computer, using a large checkerboard, with red and blue
poker chips to represent a neighborhood's residents. Even 10 years
ago agent-based models with large populations might have required
hundreds of costly hours on supercomputers; but today's fast and
inexpensive desktop machines make this method readily available to
social scientists. These models are now being used to show how
"simple but predictable local interactions among many individuals can
generate familiar but enigmatic social patterns, such as stock market
crashes, revolutions, fads and feeding frenzies,"says Macy.
In collaboration with his Cornell colleague David Strang, Macy has
used agent-based models to study lemminglike fads among the corporate
managers pilloried by Scott Adams in his "Dilbert" comic strip.
Contrary to Adams, top managers are highly intelligent and are paid
huge salaries to get it right, Macy observes. The Cornell
researchers' work, which won the theory prize from the Academy of
Management, shows how fads that appear to reflect mindless conformity
can be generated by the very opposite -- a single-minded
preoccupation with performance and success.
Macy recently was awarded a grant from the National Science
Foundation to tackle another familiar puzzle -- peer enforcement of
norms that even the enforcers privately question. In collaboration
with two Cornell graduate students, Robb Willer and Damon Centola,
Macy is using an agent-based model to see how the diffusion and
stability of unpopular norms might depend on the size and geometry of
peer networks. The father of teenagers, Macy ponders the curious
appeal of self-destructive behaviors -- smoking, drinking, drug use,
reckless driving, body-piercing and the like. For example, studies of
college drinking find that students feel peer pressure to participate
in drinking rituals that celebrate intoxication as a symbol of group
identity.
"Yet it turns out that students' private beliefs deviate sharply from
their perception of the social norm," he notes. "Contrary to campus
legend, most students are actually uncomfortable about excessive
drinking, at least when they are sober. They do not think drinking
games are cool, but they think (incorrectly) that others believe
this, and when they join in to secure social approval, their apparent
enthusiasm reinforces the illusion that motivates the behavior in
others."
When Macy's team (<http://people.cornell.edu/pages/mwm14/>) tried to
generate this dynamic on a computer, the agents always escaped the
trap. But then the researchers remembered a lesson taught by
Reynolds' boids. "The boids only know about the behavior of their
immediate neighbors, and that turns out to be the key to the puzzle,"
Macy says. "Agents get trapped into enforcing a norm that most of
them dislike when their normative expectations are mainly influenced
by a small circle of friends."
-30-
The web version of this release may be found at
http://www.news.cornell.edu/releases/Feb03/AAAS.Macy.hrs.html
Cornell University News Service
Surge 3
Cornell University
Ithaca, NY 14853
607-255-4206
cunews_at_cornell.edu
http://www.news.cornell.edu
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