STUDIES OF CEREBRAL FUNCTION IN LEARNING. VII 



29 



In order that cortical blindness should produce the results 

 obtained, the following conditions must be met: The lesions 

 must produce areas of scotoma proportional in size to the 

 extent of the injury. With such totally blind areas in the 

 visual field the chances that the functional area would be 

 stimulated by the light in any given trial might be inversely 

 proportional to the size of the scotomatous areas. Animals 

 with large injuries would tend to make more errors. Im- 

 provement during the retention tests would consist in the 

 animal's learning to fixate the stimulus light with the intact 

 parts of the retina. 



Text fig. 5 Composite diagram made by superimposing the diagrams of the 

 lesions in all cases of group B which made not more than five errors in retention 

 tests. Every part of the occipital third of the cerebrum was destroyed in 

 one or another of these cases without serious deterioration of the habit. 



Several considerations oppose this view and, I believe, make 

 it untenable: 1) No part of the behavior of the animals in 

 retention tests suggests this adaptation in fixation. The 

 rat's eye can be rotated only slightly and fixation involves 

 orientation of the head, but no unusual postures were ever 

 noted in the operated animals. 2) If the difficulty in discrimi- 

 nation had resulted from scotoma, it should have appeared 

 in the learning of group A as well as in the retention tests 

 of group B, since scotoma is equally a blindness to new and 

 to familiar objects. No influence of the lesion was apparent, 



