Seite 7: Self-organisation

Evolution and co-evolution are in themselves not enough. Usually there are many possible structures which are equally plausible from the viewpoint of the selectionist criteria discussed so far. But out of the many possibilities only one is usually selected and adopted by the total linguistic population. Language and meanings are shared. This is a big puzzle for anyone who seeks a non-nativist theory of language and meaning. If meaning and language is innate then it is genetically shared and coherence comes for free. But if language and meaning are not innate we must explain how coherence may arise without central control and with agents having only access to each other's states through localised interactions.

The origins of coherence in a distributed system with many interacting elements have been studied in biology and other sciences under the heading of self-organisation. A typical example is a cloud of birds or a path formed by ants. Examples of self-organisation are also found at lower levels. For example, regular temporal or spatial patterns in the Bhelouzow-Zhabotinsky reaction or the sudden appearance of coherent light in lasers are chemical and physical examples of self-organisation.

The principle of self-organisation prescribes two necessary ingredients: there must be a set of possibile variations and random fluctuations that temporarily may cause one fluctuation to gain prominence. Most of the time these fluctuations are damped and the system is in a (dynamic) equilibrium state. However if there is a positive feedback loop causing a certain fluctuation to become enforced, then one fluctuation eventually dominates. The feedback loop is typically a function of the environment so that the self-organisation only takes place for specific parameter regimes. When these parameters are in a lower regime they leave the system in equilibrium. When the parameters are in a higher regime, they bring the system in (deterministic) chaos. Structure arises and is maintained on the edge of chaos .

In the computational experiments, self-organisation has proven to be an effective way to arrive at coherence. The positive feedback loop is based on success in games that involve multiple agents. Those rules are preferred that are the most used and the most successful in use. For example, for each word-meaning pair a record is kept how many times this pair has been used and how many times the use of the pair in a specific language game was successful. The (speaking) agent always prefers the most successful word. This causes the positive feedback effect: the more a word is used, the more successful it will be and the more it will be used even more. Initially there will be a struggle between the different word-meaning pairs until one dominates. Coherence crystallises quite rapidly once a word starts to dominate, similar to a phase transition.

The same principle can also be applied at other levels. Phonemes and phoneme segments that have most success in imitation games are preferred over those that have less success - even if they satisfy all other constraints. The coherence of meaning happens indirectly. Features are preferred that have been lexicalised and hence the most common features will be shared by all agents.