STUDIES OF CEEEBKAL FUNCTION IN LEAENING. VII 21 



THE EFFECT OF OCCIPITAL LESIONS UPON THE EETENTION OF 

 VISUAL HABITS FOKMED BEFOEE OPEEATION 



Mass relationships 



Two groups, B and C, were used for tests of retention after 

 operation. The data on them are summarized in tables 3 

 and 4. Group B constituted the chief experiment; C, the 

 control for diaschisis effects. Group B will therefore be con- 

 sidered first. The constants for the group are given below. 



Trials for learning Errors during training 

 Learning before operation, 128.2 ± 5.2 41.8 ± 2.5 



Preliminary retention tests, 1.4 ± 0.23 



Postoperative retention tests, 44.6 ± 3.4 13.7 ± 1.22 



The preliminary retention tests give a measure of the loss 

 to be expected from disuse during an interval of seven days, 

 which was that later allowed for recovery from the shock of 

 the operation. -The small number of errors made following 

 this seven-day rest period (1.4 ± 0.23) shows that the loss 

 from disuse may be treated as negligible in considering the 

 effects of operation. 



The averages of 44.6 trials and 13.7 errors in the postopera- 

 tive retention tests show that, on the average, a definite loss, 

 equivalent to about one-third of the effect of initial practice, 

 was produced by the operation. The lesions in this group 

 (figs. 50 to 98) form a continuous series from 1.5 to 31.9 

 per cent of the neopallium, with an average of 15.8 ± 0.69 

 per cent. They cover almost the posterior half of the cortex, 

 as shown in text figure 2. Some lesions within this range 

 therefore reduce the retention of visual habits, although, as 

 appeared in the preceding section, similar lesions have no 

 effect upon subsequent initial learning. 



Inspection of table 3 reveals the fact that many of the 

 animals with slight lesions showed no disturbance of the habit 

 following the operation, whereas those with extensive lesions 

 often required as many trials for relearning as for the initial 

 learning. This suggests a relationship between the extent of 

 lesion and the amount of loss of the habit produced by it. 

 It has been tested by computing correlations between the 



