1 70 



BRAIN MECHANISMS AND LEARNING 



stinuilus, rather than proving there were no confusing effects in the first 

 place. We have often seen animals become 'brighter' as the 'reward' 

 potentiometer is turned upwards in maze experiments. 



INCORRECT 



CORRECT 



STIM. EVERY 3 SEC. 



NO STIM. 



Fig.. 15 

 Reinforcement-interference test. 

 Interference stimulus starts when 

 animal is placed in box and con- 

 tinues unless error pedal is pressed. 

 At that point it is terminated and 

 does not start again until correct 

 response occurs. 



DISCUSSION 



At the end of the first set of experiments we were well aware that the 

 hypothalamic-rhinencephalic system was most likely the central core of 

 the positive-reinforcement mechanism. And wc also thought in terms of 

 positive reinforcement as involving (i) some close relationship to learning 

 (a concept we still hold) and (2) some peculiar virtue in promoting learn- 

 ing, sharpening the wits, oiling the course, or stamping in the right 

 response. 



The second set of experiments surprised us at first, indicating as it did 

 that the most efficacious way to interfere with the learning mechanism 

 was to hyperstimulate the same system which we had formerly thought 

 to promote learning. We should not have been surprised, of course, for 



