DESIGN FOR A BRAIN 3/12 



Again they ran to it, shovelling along the bottom with their 

 beaks, and squatting down in it. But they soon gave up. 

 On the third morning they waddled up to the dry tin, and 

 departed.' 



Their behaviour at first suggested that there was no feedback. 

 But on the third day their change of behaviour showed that, in 

 fact, the change in the bath had had some effect on them. 



The importance of feedback lies in the fact that systems which 

 possess it have certain properties (S. 4/16) which cannot be shown 

 by systems lacking it. Systems with feedback cannot adequately 

 be treated as if they were of one-way action, for the feedback intro- 

 duces properties which can be explained only by reference to the 

 particular feedback used. (On the other hand a one-way system 

 can, without error, be treated as if it contained feedback: we 

 assume that one of the two actions is present but at zero degree 

 (S. 2/3). In other words, systems without feedback are a sub- 

 class of the class of systems with feedback.) 



3/12. As the organism and its environment are to be treated as a 

 single system, the dividing line between ' organism ' and ' environ- 

 ment ' becomes partly conceptual, and to that extent arbitrary. 

 Anatomically and physically, of course, there is usually a unique 

 and obvious distinction between the two parts of the system; but 

 if we view the system functionally, ignoring purely anatomical 

 facts as irrelevant, the division of the system into ' organism ' and 

 4 environment ' becomes vague. Thus, if a mechanic with an 

 artificial arm is trying to repair an engine, then the arm may be 

 regarded either as part of the organism that is struggling with 

 the engine, or as part of the machinery with which the man is 

 struggling. 



Once this flexibility of division is admitted, almost no bounds 

 can be put to its application. The chisel in a sculptor's hand 

 can be regarded either as a part of the complex biophysical 

 mechanism that is shaping the marble, or it can be regarded as 

 a part of the material which the nervous system is attempting to 

 control. The bones in the sculptor's arm can similarly be regarded 

 either as part of the organism or as part of the ' environment ' of 

 the nervous system. Variables within the body may justifiably 

 be regarded as the ' environment ' of some other part. A child 

 has to learn not only how to grasp a piece of bread, but how to 



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