Value. Such are the voltage below which an arc will not jump
Across a given gap, and the damage that a citizen will sustain
Before he thinks it worth while going to law. In the nervous sys-
Tem the phenomenon of threshold is, of course, ubiquitous.
The existence of threshold induces a state of affairs that can be
Regarded as a cutting of the whole into temporarily isolated sub-
Systems; for a variable, so long as it stays constant, cannot, by S.4/
Have an effect on another; neither can it be affected by another.
In the diagram of immediate effects it will lose both the arrows
That go from it and those that come to it. The action is shown dia-
Grammatically in Fig. 4/20/1.
The left square shows a basic network, a diagram of immediate
Effects, as it might have been produced by the method of Ex. 4/19/
The middle square shows what remains if thirty per cent of the
Variables remain constant (by the disturbances that are coming to
Them being below threshold). The right square shows what
Remains if the proportion constant rises to fifty per cent. Such
Changes, from left to right, might be induced by a rising threshold.
It will be seen that the reacting sub-systems tend to grow smaller
And smaller, the rising threshold having the effect, functionally, of
Cutting the whole network into smaller and smaller parts.
Thus there exist factors, such as “height of threshold” or “pro-
Portion of variables constant”, which can vary a large system con-
Tinuously along the whole range that has at one end the totally
Joined form, in which every variable has an immediate effect on
66
67
Figure 4/20/1
A N I N T R O D UC T I O N T O C Y B E R NE T I C S
TH E MA C HI N E WI TH I N PUT
Every other variable, and at the other end the totally-unjoined
Form, in which every variable is independent of every other. Sys-
Tems can thus show more or less of “wholeness”. Thus the degree
May be specifiable statistically even though the system is far too
Large for the details to be specified individually.
Ex.: Can a disturbance a: A (Fig. 4/20/1) affect B in the left-hand system? In the
Other two?
Cies are more or less alike. In this system various properties, if
|
|
|
They exist in one place, can also exist in other places. It follows
That the basic properties of the biological world will be of the
Types to be described in the following sections.
Self-locking properties. It is a general property of these sys-
Tems that their behaviour in time is much affected by whether
There can, or cannot, develop properties within them such that the
Property, once developed, becomes inaccessible to the factors that
Would “undevelop” it. Consider, for instance, a colony of oysters.
Each oyster can freely receive signals of danger and can shut
Close; once shut, however, it cannot receive the signals of safety
That would re-open it. Were these the only factors at work we
Could predict that in time the colony of oysters would pass entirely
into the shut condition— an important fact in the colony’s history!
In many other systems the same principle can be traced more
Seriously, and in almost all it is important. Consider, for instance
A solution of reacting molecules that can form various compounds
Some of which can react again but one of which is insoluble, so
That molecules in that form are unreactive. The property of “being
The insoluble compound” is now one which can be taken by part
After part but which, after the insolubility has taken the substance
Out of solution, cannot be reversed. The existence of this property
Is decisive in the history of the system, a fact well known in chem-
Istry where it has innumerable applications.
Too little is known about the dynamics of the cerebral cortex for
Us to be able to say much about what happens there. We can how-
Ever see that if the nerve cells belong to only a few types, and if
The immediate effects between them are sparse, then if any such
“self-locking” property can exist among them it is almost certain
|
|
|
To be important— to play a major part in determining the cortex’s
Behaviour, especially when this continues over a long time. Such
Would occur, for instance, if the cells had some chance of getting
Дата добавления: 2019-11-16; просмотров: 211; Мы поможем в написании вашей работы! |
Мы поможем в написании ваших работ!