Modification by Experience 261 



hand, Thorndike (708) successfully carried out this kind of 

 training with Cebus monkeys : both of his subjects learned 

 to come down to the bottom of the cage for food when the 

 experimenter took the food in his right hand, and to stay 

 up when he took it in his left hand, the food being withheld 

 if the monkeys came for it in the second case. Cole (134) 

 trained raccoons to climb up on a box for food when one of 

 two differently colored cards was shown, and to stay down 

 when the other one appeared, by not feeding the raccoons if 

 they climbed up for the wrong card. 



The dropping off of movements takes place with more 

 speed and certainty if they are made to give place, not 

 simply to a state of no movement at all, but to a movement of 

 greater prepotency than their own. Especially effective in 

 thus causing the elimination of a movement is the negative 

 reaction of withdrawal from injury. Thus if a movement 

 A results in actual harm to the organism, the harmful stimu- 

 lus thus produced brings about the negative response ; and 

 the negative reaction is as a rule prepotent over all others. 

 The next time the movement A is initiated, the negative 

 reaction is also initiated, and being prepotent, it is able 

 to check effectively the performance of movement A. 

 Thus we have the dropping of of harmful movements, a 

 process which is in evidence whenever punishment is used 

 in studying the learning power of animals. It also ap- 

 pears when a successful negative reaction permanently 

 takes the place of unsuccessful ones. We saw in the first 

 part of this chapter that when an animal is repeatedly sub- 

 jected to a strong and harmful stimulus, it goes through 

 a series of reactions, all directed to getting rid of the stimu- 

 lus, until one is finally successful. Now if this process is 

 shortened in successive trials, so that the successful nega- 

 tive reaction comes to be made at once and the unsuccess- 



