ChaOs (an acronym for Chemical Oscilator) is a metaphorical model of a neurophysiological phenomenon known as a neural reverbatory circuit [21, 22]. ChaOs can be thought of as an array of identical electronic circuits called nerve cells. At a certain moment, nerve cells can be in one of the following states:quiescent, depolarised or burned. It tends to evolve from an initial random distribution of cells' states in the grid, to an oscillatory cycle of wave patterns (Figure 1). The behaviour of ChaOs resembles the way in which most of the natural sounds produced by acoustic instruments evolve: they tend to converge from a wide distribution of their partials (for example, noise) to oscillatory patterns (for example, a sustained tone).
Figure 1: The bahaviour of ChaOs when it reaches an oscillatory state.
A nerve cell interacts with its neighbours through the flow of electric current between them (Figure 2). There are minimum (Vmin) and maximum (Vmax) threshold values which characterise the state of a nerve cell. If its internal voltage (Vi) is under Vmin, then the nerve cell is quiescent (or polarised). If it is between Vmin (inclusive) and Vmax values, then the cell is being depolarised. Each nerve cell has a potential divider which is aimed at maintaining Vi below Vmin. But when it fails (that is, if Vi reaches Vmin) the nerve cell becomes depolarised. There is also an electric capacitor which regulates the rate of depolarisation. The tendency, however, is to become increasingly depolarised with time. When Vi reaches Vmax, the nerve cell fires and becomes burned. A burned nerve cell at time t is automatically replaced by a new quiescent cell at time t + 1.
Figure 2: The interaction of nerve cells
The bahaviour of ChaOs is specified by setting up a number of parameters:
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