22 K. S. LASHLEY 



extent of lesion and the scores made in postoperative reten- 

 tion tests by all the animals. Rank order and product- 

 moment methods have both been employed. The results by the 

 two methods are identical to the second decimal, so only the 

 former are given below. 



Extent of lesion with trials for relearning, p = 0.712 ± 0.047 

 Extent of lesion with errors in retraining, p ^ 0.721 ± 0.046 



These coefficients are about sixteen times as great as their 

 probable errors, and therefore clearly significant. They in- 

 dicate a close relationship between the extent of injury and 

 the amount of deterioration of the habit formed before 

 operation. 



The data in table 3 suggest that the relationship may not 

 be rectilinear and, to test this, correlation ratios have been 

 computed for trials and errors on per cent destruction. The 

 constants obtained were the following : 



Trials on per cent, t? = 0.828 ± 0.030 

 Errors on per cent, t? = 0.841 ± 0.028 



The correlation ratios are considerably larger than the coeffi- 

 cients, but the difference is only 1.9 times its probable error 

 (Blakeman's formula) and is not sufficient to establish the 

 curvilinear character of the relationship. 



Possible causes of spurious correlation 



Measured by either of these constants, the relationship be- 

 tween memory loss and extent of injury is surprisingly close. 

 Is it due to the actual removal of cerebral tissue or only to 

 some secondary effects of the operation, such as general 

 shock or diaschisis? The possible secondary factors which 

 might produce a spurious relationship are : 



1. General shock from operation and irritation of the wound. 

 In an earlier paper (Lashley, '21) I have shown that exten- 

 sive lesions to the frontal lobes and corpus striatum may pro- 

 duce little disturbance of visual discrimination. Judged from 

 its general effects, this is a very much more severe operation 

 than even the extensive occipital ones, yet the effects were 



