Stigmergy

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Stigmergy is a method of indirect communication in a self-organising emergent system where its individual parts communicate with one another by modifying their local environment.

Stigmergy was first observed in nature - ants communicate to one another by laying down pheromones along their trails, so where ants go within and around their ant colony is a stigmergic system. Similar phenomena are easily seen in many (all?) eusocial creatures, such as termites, who use pheromones to build their very complex nests by following a simple decentralized rule set. Each insect scoops up a 'mudball' or similar material from its environment, invests the ball with pheromones, and deposits it on the ground. Termites are attracted to their nestmates' pheromones and are therefore more likely to drop their own mudballs near their neighbors'. Over time this leads to the construction of pillars, arches, tunnels and chambers.

1 History
2 Application
3 Notes
4 See also
5 External links

[edit] History

The term was introduced by French biologist Pierre-Paul Grassé in 1959 to refer to termite behavior. He defined it as: "Stimulation of workers by the performance they have achieved." It is derived from the Greek words stigma ‘sign’ and ergon ‘action,’ and captures the notion that an agent’s actions leave signs in the environment, signs that it and other agents sense and that determine their subsequent actions.” ^[1]

[edit] Application

Stigmergy is not restricted to eusocial creatures, or even to physical systems. On the Internet there are many emergent phenomena that arise from users interacting only by modifying local parts of their shared virtual environment. Wikipedia is a perfect example of this. The massive structure of information available in a wiki could be compared to a termite nest; one initial user leaves a seed of an idea (a mudball) which attracts other users who then build upon and modify this initial concept eventually constructing an elaborate structure of connected thoughts.

The term is also employed in experimental research in robotics, multi-agent systems and communication in computer networks. In these fields there exist two types of stigmergy: active and passive. The first kind occurs when a robotic or otherwise intelligent "agent" alters its environment so as to affect the sensory input of another agent. The second occurs when an agent's action alters its environment such that the environmental changes made by a different agent are also modified. A typical example of active stigmergy is leaving behind artifacts for others to pick up or follow. An example of passive stigmergy is when agent-A tries to remove all artifacts from a container, while agent-B tries to fill the container completely.

[edit] Notes

^ Parunak, H. v D. (2003). Making swarming happen. In Proc. of Conf. on Swarming and Network Enabled Command, Control, Communications, Computers, Intelligence, Surveillance and Reconnaissance (C4ISR), McLean, Virginia, USA, January 2003.