DESIGN FOR A BRAIN 3/11 



type problem of the kitten and the fire. The various stimuli 

 from the fire, working through the nervous system, evoke some 

 reaction from the kitten's muscles; equally the kitten's move- 

 ments, by altering the position of its body in relation to the fire, 

 will cause changes to occur in the pattern of stimuli which falls 

 on the kitten's sense-organs. The receptors therefore affect the 

 muscles (by effects transmitted through the nervous system), and 

 the muscles affect the receptors (by effects transmitted through 

 the environment). The action is two-way and the system possesses 

 feedback. 



The observation is not new: 



4 In most cases the change which induces a reaction is brought 

 about by the organism's own movements. These cause a 

 change in the relation of the organism to the environment: 

 to these changes the organism reacts. The whole behaviour 

 of free-moving organisms is based on the principle that it 

 is the movements of the organism that have brought about 

 stimulation.' 



(Jennings.) 



' The good player of a quick ball game, the surgeon con- 

 ducting an operation, the physician arriving at a clinical 

 decision — in each case there is the flow from signals inter- 

 preted to action carried out, back to further signals and on 

 again to more action, up to the culminating point of the 

 achievement of the task '. 



(Bartlett.) 



1 Organism and environment form a whole and must be 

 viewed as such.' 



(Starling.) 



It is necessary to point to the existence of feedback in the 

 relation between the free-living organism and its environment 

 because most physiological experiments are deliberately arranged 

 to avoid feedback. Thus, in an experiment with spinal reflexes, 

 a stimulus is applied and the resulting movement recorded; but 

 the movement is not allowed to influence the nature or duration 

 of the stimulus. The action between stimulus and movement is 

 therefore one-way. A similar absence of feedback is enforced 

 in the Pavlovian experiments with conditioned reflexes: the 

 stimulus may evoke salivation, but the salivation has no effect 

 on the nature or duration of the stimulus. 



Such an absence of feedback is, of course, useful or even essen- 



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