96 K. S. LASHLEY 



the illuminated alley with a rush. Training was continued for only 

 50 trials, which did not permit of perfecting the habit but the secondary 

 evidence of discrimination is conclusive. 



Lesion: Plate III, figure 4. The frontal poles of both hemispheres 

 in front of and above the knee of the corpus callosum were completely 

 severed from the remainder of the brain, by an incision which passed 

 through the olfactory tracts. 



The total extent of the lesion in these animals is shown in 

 figure 10. The average percentage of errors made on successive 

 days by the normal and operated animals in these experiments 

 is given in table 5. There is no very marked difference in the 

 amount of improvement shown by the two groups from day to 

 day. 



FIG. 10. THE TOTAL EXTENT OF THE LESIONS IN ANIMALS WHICH FORMED THE 

 HABIT OP VISUAL DISCRIMINATION AFTER OPERATION 



The stippled area represents the animal with which training was not completed. 



The average number of trials required by the normal animals 



for learning the visual habit was 106.6 with a range from 60 to 



130. The average number required by the operated animals was 



80, with a range from 70 to 100. The operated animals thus show 



pa superiority of 26.6 trials, or 24.9 per cent, over the normal ani- 



( mals. As in the experiments with the double-platform box, the 



operated animals are superior in learning ability to the normal 



controls. 



In this case, however, the explanation offered before for the 

 superiority of the operated animals does not hold good. The 

 discrimination habit does not seem to be influenced by the rela- 

 tive activity, or vigor, of the animals and the use of a constant 



