CEREBRAL FUNCTION IN LEARNING 73 



animals it would have been impossible to distinguish the oper- 

 ated animals from normals on the basis of any instinctive reac- 

 tion, when once the immediate effects of the operation had worn 

 off. (That the lack of motor coordination may lead to mistaken 

 interpretation of other behavior has already been pointed out.) 

 There is no evidence for any disturbance in instinctive reactions 

 which might account for marked difference in learning ability. 



III. THE EFFECT OF CEREBRAL INJURY UPON LEARNING ABILITY 



Problem and methods 



The first group of training experiments sought to measure 

 the effect upon learning ability of the removal of various por- 

 tions of the cerebral cortex, to determine whether or not any 

 particular part of the cerebrum is necessary or is especially 

 well adapted to the formation of complex habits. The method 

 adopted was that of destroying a definite area of the cortex in 

 each of a number of animals, varying the operations so as to 

 cover all regions of the cortex in the total series of experiments; 

 then to train the operated animals and compare their rates and 

 methods of learning with those of normal animals. 



Since there is a possibility that some simple habits are acquired 

 wholly at subcortical levels (Franz and Lashley, '17) it seemed 

 desirable to use a complicated problem for training. A second / 

 requirement of the problem to be learned was that it should ; 

 demand some definite series of acts which could be recognized 

 easily and which would be unlikely to appear as the result ofi 

 pure chance, since the same problem was to be used for learning j 

 and for retention tests and time and error criteria alone are not 

 very reliable tests of retention when applied to animals suffering \ 

 from shock and motor disturbances following operation. A third 

 requirement of the problem was that it should offer equal chances 

 for learning to normal animals and to those which were weak 

 as the result of operation. The inclined plane box with the j 

 plane situated above the door, used previously by Lashley and 

 Franz, was not very satisfactory, since the operated animals 

 sometimes had difficulty in climbing up to the plane. 



