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Communication and Information

Information consists of signs that follow certain rules in order to be understandable. The information theory distinguishes between languages that evolved over a long period of time and codes that have been developed for certain purposes. Information is measured in bit. Redundancy or repetition is surplus information.

Control processes cannot be understood in detail, if the meaning of information is not completely clear. The exchange of information between individuals (or functional elements) is called communication. Communication is based on the transmission of information that consists of signs. Each sign stands for or speaks of something. An information can therefore be regarded as a sum of signs. Information as such can neither be captured physically nor energetically.

The assignment of an information to a certain physical state is called coding. Each sign carries a meaning and is thus part of a signal. The letters of an alphabet are signs.

Code: The information theory distinguishes between languages that have evolved during historical periods of time and codes that have been developed for special purposes. But in a strictly formal sense, a language is a code, too. Probably the most famous natural code (according to the information theory a language) is the genetic code. The genetic information that is stored in the DNA with a content of four nucleotide signs is used for the production of proteins with a content of 20 amino acids signs.

Code and signal: Rules are necessary for the representation of a code. Only 'allowed' combinations of signs that can be understood by the recipient form a 'signal'. The generation of a multicellular organism demands a communication between the cells. In the simplest case, a cell produces a substance like, for example, a growth regulator (e.g. a phytohormone) that is excreted by a cell (the sender or elicitor) and recognized or taken in by another cell (the recipient) eliciting a certain reaction like enhanced or reduced growth. The recognition of such a signal requests the existence of specific and selective receptors in the recipient that identify the signal but no other molecule.

Transmission of information: The path between sender and recipient is called channel, the relation between information and signal is communication. Many mistakes may occur on the way, information can be lost or falsified.

Quantitative processing of information: Information is measured in bit. If two events P₁ and P₂ have the same probability of occurrence, then the exact knowledge about the occurrence of one of these events is 1 bit. In a given set of events A = (1, 2, 3, 4,.....) with the same probability of occurrence is the knowledge that one of these events occurs 3 bit information. To put it another way:

I = ₂log 8 = 3 bit

The log of the base 2 is often also called ld (logarithmus dualis), expressed this way I is:

I = ld 8 = 3 bit

n bits means a choice of n alternatives.

A closer examination shows that a connection between an event and the probability of its occurrence exists. The bigger the probability of an event the smaller its information value. The information of an event x is therefore the ld of the reciprocal value of the probability of its occurrence.

I(x_j)= ld 1/p x_i

The average content of information of a set of n events x_i (i= 1,2,...n) with the probability p(x_i) is the expected value of the information of the single results (H), defined as:

H = sum (n > i) p (x_i) ld l/p (x_i)

The positive difference between the average information content at a time t₁ minus the average information content at a time t₂ is called the gain of information.

Redundancy

Redundancy (= repetition) is surplus information. It depends on the probability of an information or sign. There exists consequently a direct link between it and the information. Redundancy serves to safeguard transmission mistakes (disruptions). Genetics especially is full of examples:

1. Somatic cells of higher organisms are usually diploid. A defect allele (a) can be compensated by the simultaneous presence of a homologous intact partner chromosome (A).

2. Micro-organisms are normally haploid. Mistakes are compensated by large numbers of individuals. Such a strategy of propagation is impossible for multicellular organisms. The long generation period (weeks, months, years) and the large amount of energy needed to generate and keep up the function of the organism stand in the way of such a strategy. In the course of evolution, mechanisms have developed to preserve genetic information and to eliminate mistakes occurring during its copying.

3. Redundancy at the level of the genetic code: A considerable amount of point mutations shows no effect whatsoever. There are numerous, energy-consuming repair mechanisms to clear mistakes occurring when reading or replicating genetic information.

4. Too much redundancy may not be beneficial any more. Polyploidy is widespread in certain plants. The probability that a new combination wins through is therefore very low. Expressed in another way : their evolutionary potential is relatively small when compared to diploids.

Redundancy can also be found in the development of plant organs. In most cases, a plant does not need as many leaves and such a high rate of assimilate production to develop enough seeds well equipped with nutriments.

These few examples show how many aspects regulation has. The question of the mechanisms of regulation arises hence in all physiological processes. Cybernetics offers a framework where observations and experimentally gained data find a place. The complexity of the image grows with an increasing number of data. Natural scientists will always only be able to analyze and understand parts of systems.