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Robert Goldstone
Cognitive Science Program

Tracy James
IU Media Relations

Last modified: Thursday, August 31, 2006

The path of least resistance: A study of where we go

IU cognitive scientists examine the makings of pathways and progress

Sept. 6, 2006

Path image

Graduate student Michael Roberts (left) and Professor Robert Goldstone stand by a self-organized trail used by IU students who walk near the home of the university president.

Print-Quality Photo

BLOOMINGTON, Ind. -- Indiana University researchers tap cyberspace and biophysics along with insights from poets and former president Dwight D. Eisenhower to examine how existing paths, regardless of how meager, influence travel and nothing less than future progress.

When Eisenhower was a university president, he was asked how the university should arrange the sidewalks to best interconnect the campus buildings. He responded that they should first plant grass seed, let the grass grow, see where the grass became worn by people's footsteps and then install the sidewalks in the most worn patches.

The Percepts and Concepts Laboratory at IU Bloomington put Eisenhower's proposal to the empirical test, examining the kinds of trails 300-plus college students would form when motivated to take advantage of the trails left by their predecessors. The researchers then borrowed from biophysics to model the results. The model, which assumes that travelers' steps are a compromise between going where they want to go and where others have gone before -- and has been applied to ant trails -- essentially reproduced the trails the student groups formed.

"When people behave in groups, they constrain each other so that the entire group's behavior is highly predictable, even by models of physics for simple molecules," said Robert Goldstone, director of IUB's Cognitive Science Program and the Precepts and Concepts Laboratory.

The trails that experimental groups created were compromises between people going directly to their destinations and taking paths of least effort, Goldstone and graduate student Michael Roberts wrote in "Self-organized Trail Systems in Groups of Humans," the cover story of the July/August issue of the journal Complexity. The trail network that completely connects a set of destinations using the minimal amount of total trail length is called a Minimal Steiner Tree. While soap films reliably create Minimal Steiner Trees, Goldstone and Roberts' human collectives did not. However, their paths did deviate away from beeline paths to destinations in the direction of Minimal Steiner Trees.

Goldstone and Roberts conducted a group experiment in which IU students collectively traveled to random destinations in a virtual world. As they stepped on a location, they changed their environment, making it easier for subsequent walkers to step on the same location. In this way, a trail left by a walker often led other walkers to follow the same trail, thereby reinforcing and extending the trail. The students also were motivated by savings -- they were tasked with reaching their destinations at the least cost, with the most traveled routes costing them less.

"Early trail blazers through a jungle use machetes to make slow progress in building paths -- progress that is capitalized on and extended by later trekkers, who may then widen the trail, then later put stones down, gravel, asphalt and eventually an eight-lane highway," the researchers wrote in Complexity. Technological advances, Goldstone said, largely pursue paths of previous innovations and extend them, fueled by the same "popularity advantage," or ideational stigmery, where people make choices based on the choices of their forbearers.

"The growth of our collective spatial path systems may reveal principles about how future progress is more generally achieved by exploiting and extending prior innovations," the researchers wrote.

In a more immediate sense, their findings could influence crowd control practices because of their insights into controlling collective behavior. The researchers' experiments and simulations, Goldstone said, also provide a rigorous way of following the poet Antonio Machado's exhortation: "Traveler, there is no path. Paths are made by walking."

For a copy of the journal article, visit

Goldstone can be reached at 812-855-4853 or Visit the Percepts and Concepts Laboratory at