9/5 DESIGN FOR A BRAIN 



at the minnows he struck the glass. The following immediate 

 effects can be clearly distinguished : 



The arrow 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 led 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 few nibbles the carrot was withdrawn and the process repeated.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 serves 

 merely to call this dynamic system into functional existence ; 

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



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