STUDIES OF CEREBRAL FUNCTION IN LEARNING 



259 



experimental lesions described below are restricted to the caudate 

 nucleus and this is also the part whose injury produces paralytic 

 symptoms [10, 12]. 



Experimental Methods. 



Training. — For the study of visual habits a discrimination box of 

 the type designed by Yerkes was used. It consists of a central com- 

 partment opening into two parallel alleys which lead by lateral passages 



Fig. 2. — Composite diagram of the lesions in animals which retained the habit of visual 

 discrimination after operation. The habit survived the destruction of any third of the 

 blackened area. 



Fig. 3. — Composite diagram of the lesions in seven animals which lost the habit of visual 

 discrimination after operation. The area which was destroyed in all is shown in solid black. 



to compartments in which food is placed. At the end of each alley is 

 a small electric bulb, 5-watt frosted " Mazda," visible from the dis- 

 crimination compartment. One bulb is lighted and the other darkened 

 in irregular alternation and the animal is trained to choose the illu- 

 minated alley, receiving food there and punishment in the darkened 

 one. Training was continued with ten trials per day by the usual 

 method of irregular alternation until the animals made thirty consecu- 

 tive trials without entering the darkened alley. Controls were intro- 



