STUDIES OF CEREBRAL FUNCTION IN LEARNING. VII 



31 



The same objection holds for the hypothesis that the quan- 

 titative results are due to a total amblyopia proportional in 

 severity to the extent of the lesions. These should likewise 

 have affected equally the learning and retention tests. Thus, 

 as I have pointed out in an earlier paper (Lashley, '20), the 

 rapid formation of visual habits in the rat after destruction 

 of the occipital region of the cortex shows that the sensitivity 

 of the animals to visual stimuli is unimpaired ; only the reten- 

 tion of habits formed before the injury is affected. The 

 present experiment seems to establish this fact beyond ques- 

 tion. It is the mechanism which maintains the organization 

 of the habit, the engram in Semon's terminology, and not the 

 mechanism of visual sensitivity which is destroyed. 



Text fig. 6 Composite diagram, showing the total extent of lesions in the 

 frontal, temporal, and parietal regions which produced no significant effect upon 

 the habit of brightness discrimination. 



The relation of hahit deterioration to the locus of the injury 



The location of the visual area in the rat's brain can be 

 determined only by inference from the effects of cerebral 

 injuries. As I have shown in earlier papers (Lashley, '20, 

 '21), the habit of brightness discrimination survives the de- 

 struction, singly, of the frontal, temporal, and parietal areas 

 over the region illustrated in text figure 6. Experiments 

 reported earlier and group B of the present series demon- 

 strate that extensive destructions in the occipital third of 



THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 41, NO. 1 



