DESIGN FOR A BRAIN 



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The effect 1 represents the control exerted through spinal cord 

 and motor nerves. Effect 2 is discontinuous but none the less 

 clear: the experiment implies that some activities Jed to a high 

 pressure on the nose while others led to a zero pressure. Effects 

 3 and 4 are the simple neuro-physiological results of pressures 

 on the nose. 



Although the diagram has some freedom in the selection of 

 variables for naming, the system, regarded as a whole, clearly 

 has feedback. 



In other training experiments, the regularity of action 2 

 (supplied above by the constant physical properties of glass) may 

 be supplied by an assistant who constantly obeys the rules laid 

 down by the experimenter. Grindley, for instance, kept a 

 guinea-pig in a silent room in which a buzzer was sounded from 

 time to time. If and only if its head turned to the right did a 

 tray swing out and present it with a piece of carrot; after a few 

 nibbles the carrot was withdrawn and the process repeated. 

 Feedback is demonstrably present in this system, for the diagram 

 of immediate effects is: 



The buzzer, omitted for clarity, comes in as parameter and serve 

 merely to call this dynamic system into functional existence; 

 for only when the buzzer sounds does the linkage 2 exist. 



This type of experiment reveals its essential dynamic structure 

 more clearly if contrasted with elementary Pavlovian condition- 

 ing. In the experiments of Grindley and Pavlov, both use the 

 sequences '. . . buzzer, animal's response, food . . .' In Grind- 

 ley's experiment, the value of the variable ' food ' depended on the 

 animaVs response: if the head turned to the left, ' food ' was ' no 

 carrot ', while if the head turned to the right, ' food ' was ' carrot 

 given '. But in Pavlov's experiments the nature of every stimulus 

 throughout the session was already determined before the session 

 commenced. The Pavlovian experiment, therefore, allows no 



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