b K. S. LASHLEY 



of animals is required (more than 150 have been trained and 

 operated to obtain the present series) for a quantitative 

 study, and for this reason rats are the best available material. 

 The visual habit is the only one which has been localized with 

 any certainty in the cerebral cortex of the rat, so that there 

 was, in fact, little choice in the matter. The primitive char- 

 acter of vision in the rat (Lashley, '12) makes it impossible 

 to generalize from it to man, but, on the other hand, the very 

 simplicity of the function makes it more suitable for this 

 work, since it eliminates in part the problem of subordinate 

 localization within the visual field (v.i.). 



Studies of neural function in lower mammals constitute 

 at best only a preliminary survey, suggesting and defining 

 problems and methods which may later serve as a starting- 

 point for work with higher forms, rather than giving laws 

 of universal applicability. We must always question whether 

 principles of neural action derived from studies of the rat 

 will hold true for primates and can answer only by repeating 

 the experiments with the higher forms. Nevertheless, the 

 agreement thus far obtained when comparable experiments 

 have been performed (Lashley and Franz, '17; Franz, '07; 

 Lashley, '21, '24 a) suggests a very close similarity between 

 the higher and lower mammals in all fundamental mechan- 

 isms. Differences seem to be matters of relative differentia- 

 tion of functions rather than radical changes in mechanism. 



EXPERIMENTAL METHODS 



Training 



The rats were trained in a Yerkes' discrimination box to 

 enter a compartment illuminated directly with a frosted 

 6-watt miniature lamp and to avoid a darkened compartment. 

 In previous studies I have used this box only for qualitative 

 work, to detect the presence or absence of the habit of reacting 

 to brightness. In the present study quantitative results are 

 sought; measures of the amount of practice necessary to 

 establish the habit and of the amount of loss subsequent to 



