208 BRAIN MECHANISMS AND LEARNING 



the animal responds with a positive motor ahmentary reaction to a 

 feeding-trough either on the right or left side according to the side on 

 which the animal was fed during the application of the given conditioned 

 stimulus. 



Let us assume that with a flash of light the ciog was always fed from the 

 right-hand trough, whereas \\'ith the sound of the tone of 'C it was given 

 food in the left-hand trough. According to the law of the conditioned 

 reflex, the animal responds to this form of experiment by elaborating 

 precise conditioned motor reactions to the right and left sides of the stand. 



As soon as these conditioned reactions are firmly fixed the food is 

 suddenly (!) given to the flash of hght on the left rather than on the right 

 side of the stand. 



hi other words, an operation is performed or, in the terminology of the 

 Pavlovian laboratory, the conditioned reflex is 'reshaped'. 



hi this form of experiment it is possible to see that the animal frequently 

 fails to take food from the trough on the side that does not correspond to 

 the conditioned signal. For a long time it looks alternately to the right and 

 left feeding-troughs (orienting-investigatory reaction) and begins to eat 

 the food only after a long latent period. Additional investigations of the 

 animars respiratory component, when the side on which the food rein- 

 forcement is made is suddenly changed, show the animal to exhibit an 

 uncommonly pronounced oricntihg-investigatory reaction with a 

 strongly marked inspiratory tonus in breathing. 



The only cause that could be tliought of for this pronounced reaction 

 was the lack of corrcspoiidciice hctwccu the sudden feediui^ {return affereiitation) 

 and the already prepared complex of afferent excitations in the cerebral cortex in 

 accordance with the place of the old and usual feedino (acceptor of action). Tlic 

 same conclusion is suggested by the fact that both food reinforcements, 

 on the right as well as on the left sides, are essentially of the same signifi- 

 cance to the animal, the distances from both feeding-troughs also being 

 the same. 



The only remaining cause is the lack of correspondence between the 

 already prepared acceptor of action and the afferent influences emerging 

 when the animal is fed on the inadequate side. 



The method of sudden replacement of the rehiforccment may be used 

 in most diverse variations, especially in experiments c:>n human adults and 

 children. For example, by showing some daintv to a child and placing this 

 dainty, so that the child sees it, in a 'problem box' from which the child 

 extracts it, it is possible finally to establish adequate correlations between 

 the sight of the daiiity and the subsequent reinforcement wliich occurs 



