VISION IN THE MOUSE 



567 



A preliminary test of 50 trials was made with each animal to 

 see if any natural preference for either of the two colored lights 

 existed. The mice were found negative in this respect. Under 

 the circumstances, it is evident that the problem resolves itself 

 into the question whether the mouse can be trained to prefer one 

 quality of light to another. This is to be done by the association 

 of pleasure or pain with whatever distinguishing characteristics 

 the lights may present to the eye of the animal. Just what the 

 distinguishing characteristics are — what factors the mouse uses 

 in discriminating — may be suggested by the use of check tests, 

 in which the relative brightness of the lights is varied. In this 

 respect the apparatus of this experiment is more satisfactory 

 than that of the first series under this problem. Yet it leaves 

 something to be desired, for if the animal's choices are determined 

 wholly by intensity, this fact would become apparent, but if 

 they are determined by more than one factor (e.g., quality and 

 intensity) as seems probable, then we can hope for results only 

 on the supposition that a point of non-discrimination may be 

 found, or better, a point of least discrimination, where a certain 

 intensitj r tends to counteract the quality which would act in part 

 as a determining factor. 



Results 



Red-green discrimination 



Green-blue discrimination 



TRAINED FOR NO. CHOICES 



R green 



G green 



C green 



M green 



D green 



F green 



