46 K. S. LASHLEY AND L. E. WILEY 



15, 16, 17, 19, 22, 48, 53, 73, 74, 82, 90, 112, 117, and 120. Many 

 of these show markedly asymmetrical lesions in the two hemi- 

 spheres, but it is possible to match almost every case with 

 another from our series having practically identical lesions 

 and a poor training record. Neither locus nor depth of lesion 

 nor injuries to subcortical structures provides any apparent 

 basis for the differences in scores. The more obvious ex- 

 planations possible for the differences are : 



1. Anatomical variation. Studies of variation in locus of 

 cytoarchitectural areas by the senior author now in progress 

 do not reveal such individual differences as would be required 

 to account for the data on behavior. 



2. Chance success in solving of the problems. Maze-learn- 

 ing scores are certainly influenced to a large extent by chance 

 factors which would seriously influence the number of errors 

 or trials in the final score, but the very high intermaze cor- 

 relations and the fact that many of the above animals showed 

 superior ability in two different mazes means that, if chance 

 determined the low scores, it was a chance discovery of some 

 general principle of maze running, and this, although pos- 

 sible, is difficult to fit into our present conceptions of maze 

 learning. 



3. Different animals employ differently localized cerebral 

 mechanisms in learning the maze. One animal might be 

 primarily dependent upon visual, another upon kinesthetic 

 cues and the like, and a lesion in the striate area might in 

 consequence markedly affect the former and leave the latter 

 unaffected. Such an hypothesis is contradicted by the rela- 

 tively slight effect of sensory privation on maze learning in 

 comparison with the effects of lesions in cortical sensory 

 fields (Lashley, '31 a). An alternative would be the assump- 

 tion that the different sensory fields contribute differently 

 to maze learning in different animals in other ways than by 

 direct mediation of peripheral impulses. This hypothesis ap- 

 proaches the doctrine of image types and studies of the latter 

 have given no conclusive evidence that the image type in 

 any way correlates with the mode of learning. It is doubtful 



