Stigmergy as a Universal Coordination Mechanism (I)

Heylighen, F. . Stigmergy as a universal coordination mechanism I: Definition and components . Cognitive Systems Research (Elsevier) 38 . pp. 4-13. 2016

1. Past, present and future of the “stigmergy” concept

The concept is introduced by Pierre-Paul Grassé 1959 to describe a coordination mechanism used by insects: the work of one leaves traces in the environment that stimulates subsequent work by that insect or by others: ‘This mediation via the environment ensures that tasks are executed in the right order, without any need for planning, control, or direct interaction between agents’ [p 4]. DPB: how can execution in the right order be assured: it is not sure in what order the other agents will encounter the traces and hence in what order they will be motivated to act? From the examples in the text it appears that the stage in which work is left by the previous worker is input for the decision rules of a later worker; this implies that the stage of the work can be recognized. This is not the same as the agents assessing the stage of the work in the sense of attributing a meaning to it, or as in distinguishing this earlier stage from that later stage, because in that case the agent would have to have an idea of the finalized work and to what extent it would have to be complete in relation to the finalized work. Another example is pheromone trails left by insects and that are followed by others. These ideas can in some cases explain self-organization in social systems aka swarm intelligence (Deneubourg 1977). Conceptually a next step is computer supported collaboration between human agents, in particular via the www; another example is the establishing of a price on a market: a price emerges from the myriad of interactions between people that then serves as a reference for their decisions thereafter. DPB: anchoring means that once one has become used to some mark, it serves as a frame of reference thereafter, priming means that once a reference price was given, this serves as a frame of reference thereafter; are these stigmergic effects of a Luhmannian communication on the human mind; is spoken human language an example also, because it damages the direct environment and it only lasts as a damage in the minds of the people involved in the conversation; is written language an example in a kind of slow and long lasting way: once written its damaging effects remain forever; in that way, language (spoken or written can be deframed and reframed and be assigned a new meaning). Understood in this sense stigmergy is ubiquitous and it can clarify many things: ‘Stigmergy in the most general sense does not require either markers or quantities. Another, even more common misunderstanding is that stigmergy only concerns groups or swarms consisting of many agents. As we will show, stigmergy is just as important for understanding the behavior of a single individual’ [p 5]. The notion that an unintentional trace in a passive medium is far removed from the notion of a direct influence of the behavior of one agent on the behavior of another agent.

2 From etymology to definition

Stigmergy is derived from the Greek stigma which means mark or puncture and ergon which means work, the product of work or action: as a joint concept it was originally as a goad or prod or spur (prikkel): ‘Thus (Grassé, 1959) defined stigmergy as ‘the stimulation of workers by the very performances they have achieved (from the original English abstract)’ [p 6]. More recently it was understood as follows: ‘if we understand stigma as “mark” or “sign”and ergon as “action”, then stigmergy is “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”’ [p 6]. DPB: the understanding of Grassé is that stigmergy means motivation by the work (of others) and the understanding of Parunak is motivation by marks left by the work. Suppose an uttered word already leaves a mark on the mind of some people in a network that is the environment of someone, then the difference between the two is that in the notion of Grassé one has to be present and in the notion of Parunak one does not. DPB: the expression of a meme leads to other expressions of it. ; ‘Stigmergy is an indirect, mediated mechanism of coordination between actions, in which the trace of an action left on a medium stimulates the performance of a subsequent action’ [p 6]. Also the picture is interesting:

In the medium: a mark: which stimulates >>

In the agent: an action: which produces >> [p 6].

DPB: this is my Logistical Model exactly! Using memes it is: an expression of a meme produces a mark in a medium and a perception of that mark stimulates an action in an agent. But what I find missing here is the effect of a meme in the internal, the mark that is left within the agent. That is a difference; let’s see how the stigmergy is defined later on, and whether it includes the mind of the agent when it is included in a social system.

3. Basic components of stigmergy

Action is defined as a causal process that produces a change in the world (real). Agent is defined as a goal-directed autonomous system: this concept is not necessary because actions of a single unspecified agent can be coordinated by stigmergy (but it is useful if more than one agent is involved with different kinds of actions: stigmergy is the coordinator of actions that are merely events or (agentless) processes. This can be represented by a condition-action rule: the condition specifies the state of the world inducing the action, and the action specifies the subsequent transformation of that state. This can also be written as: a+b+c+.. >> x+y+.., where the + indicaes the conjunction of the conditions and of the actions. Chemical Organization Theory (Dittrich & Winter, 2008) show how collections of these simple reactions tend to become coordinated by acting on a shared medium (reaction vessel), where they produce an evolving trace expressed by the concentrations of the different ‘molecules’ (a,b,..). This coordinated pattern of activity defines an organization: a self-sustaining, dynamic network of interacting ‘molecules’. The relation is causal but not deterministic: the probability that an action takes place increases if the conditions are met (P (action I condition) > P (action). DPB: the medium is the whole of the environment that can contain (be damaged to show) data in the sense of a signal whether fast or slow to disappear and widely or narrowly distributed, e.g. a tombstone (in the real) or a change in the state of the mind of one’s interlocutor caused by the irritation of one’s words (in the virtual of Simondon). In the latter case the minds of the interlocutors are a part of the environment of the person: ‘The medium is that part of the world that undergoes changes through the actions and whose states are sensed as conditions for further actions’ [p 7]. The medium is an aspect of the environment: ‘First, .. , the environment is not in general perceivable an controllable. Second, the environment normally denotes everything outside the system or agent under consideration. However, stigmergy can also make use of an internal medium’ (emphasis by the author) [p 7]. DPB: waarvan acte! As a consequence aspects of the agent system are controllable by elements in the environment and hence they belong to the medium. The environment is that part of the world with which an agent interacts; phenomena perceivable and controllable are different for each agent and hence every agent has a different environment; ‘When we consider stigmergic coordination between different agents, we need to define the medium as that part of the world that is controllable and perceivable by all of them’ [p 7]. DPB: this reminds of the discourse / population idea, where a multitude of people included by a communication (the discourse) is defined as a population. This is different because in the discourse people are included that find themselves to be attracted as a result of their life experience and because of the selections of the communication. The medium is a broader and wider concept because it is determined by what people can perceive and control, but that does not necessarily attract them because of their life experience so far. The role of the medium is to allow interaction between different actions to take place, and thus, indirectly, between different agents; this mediating function is the true power of stigmergy. A final component of a stigmergic system is a trace or a mark; it is the result of an action and as such it contains information about the action that produced it: ’We might see the trace as a message, deposited in a medium, through which the pattern of activity communicates with itself, while maintaining a continuously updated “memory” of its achievements. From the point of view of an individual agent, on the other hand, the trace is a challenge: a situation that incites action, in order to remedy a perceived problem or shortcoming, or to exploit an opportunity for advancement (Heylighen, 2012)’ (emphasis by the author) [p 8]. DPB: I think in the Logistical Model the medium is the mind of the person as well as the communication: both are simultaneously and differently damaged through their mutual irritations.

4. Coordination

According to the Oxford Dictionary, coordination can be defined as the organization of the different elements of a complex body or activity so as to enable them to work together effectively’ (emphasis by the author) [p 8]. In the case of stigmergy the ‘elements’ are actions or agents; ‘effectively’ means that a goal is pursued; ‘working together’ means that the agents or actions are harmonious or synergetic ‘the one rather helping than hindering the other’ [p 8]. ‘Organization’ means a structure with a function, where ‘function’ is the achievement of the intended effect and ‘structure’ is the way agents or actions are connected such that they form a coherent whole. ‘This brings the focus on the connections that integrate the actions into a synergetic, goal-oriented whole’ (emphasis of the author) [p 8]. DPB: this reminds me of autopoietic systems: the properties of the elements of a systems determine the relations between them. The goal-orientation and the synergy (or harmony) of the elements (or rather of the body they form) is per definition dedicated to their autopoiesis.

5. The benefits of stigmergy

Stigmergic organization limits the gap between planning, instructions and reality; it is robust to contingency and shock; it is less prone to error of communication and errors of control than traditional forms of organization; it is less dependent on the number of agents or actions involved or the dependencies between them. The only requirement is that the agents have access to the medium and that they can recognize the conditions to start their actions. There is no need for: planning, memory, direct communication, mutual awareness, simultaneous presence, imposed sequence, imposed dividion of labor, commitment, centralized control.

6. Self-organization through negative feedback

Error-controlled regulation means that a deviation from the goal of an agent implies a change of behavior of the agent such that a compensatory action suppresses the effect of the deviation, the error. The agent must be capable to sense the error and to execute a compensatory action. In regards to the establishment of effective collective action, the only additional assumption is that the goals of the agents are not contradictory, but the goals are not necessary the same for it. ‘We may assume that agents have acquired their condition-action rules (and thus their implicit goals) through natural selection of instinctual behavior or differential reinforcement of learned behavior. This means that their condition-action rules are generally appropriate to the local environment, including the other agents with which they regularly interact’ [p 11]. DPB: the entire system maintains its autopoiesis and its parts maintain theirs; the entire systems develops (evolutionarily) in its environment of other systems and its parts develop in their environments of other parts; the parts develop autopoietically within the conditions of the autopoiesis of the entire system. Their ‘goals’ are their autopoiesis as it is trained to the requirements of their (local) context.

7. Self-organization through positive feedback

This is the amplification of movements towards an existing goal; they can be called diversions because they divert action from its ongoing course.

8. Conclusion

Virtually all evolved processes that require coordination between actions seem to rely at some level on stigmergy, in the sense that subsequent actions are stimulated by the trace left by previous actions in some observable and manipulable medium. The trace functions like a registry and map, indicating which actions have been performed and which still need to be performed. It is shared by all agents that have access to the medium, thus allowing them to coordinate their actions without need for agent-to agent communication. It even allows the coordination of “agentless” actions, as investigated e.g. by Chemical Organization Theory (Dittrich & Fenizio, 2007)’ [p 12]. DPB: I disagree with the ‘that require coordination’ phrase: what about a wandering discussion, where the medium involves the brains of the the other participants. This does not require coordination as such but it is coordinated.