The Sense of Sight: Brightness Vision 97 



from A to .B, and thence by way of either the right or the 

 left route to A. That the mouse should be willing to enter 

 either of the electric- boxes, after it has experienced the 

 shock, is even more surprising than its eagerness to run from 

 A to B. When first tested for brightness discrimination in 

 this apparatus, a dancer usually hesitated at the entrance to 

 the electric-boxes, and this hesitation increased rapidly un- 

 less it were able to discriminate the boxes by their difference 

 in brightness and thus to choose the right one. During the 

 period of increasing hesitancy in making the choice, the 

 experimenter, by carefully moving from / toward the en- 

 trances to the electric- boxes a piece of cardboard which 

 extended all the way across B, greatly increased the mouse's 

 desire to enter one of the boxes by depriving it of dancing 

 space in B. If an individual which did not know which 

 entrance to choose were permitted to run about in B, it would 

 often do so for minutes at a time without approaching the 

 entrance to the boxes; but the same individual, when con- 

 fined to a dancing space 4 or 5 cm. wide in front of the 

 entrances, would enter one of the electric-boxes almost im- 

 mediately. This facilitation of choice by decrease in the 

 amount of space for whirling was not to any considerable 

 extent the result of fear, for all the dancers experimented 

 with were tame, and instead of forcing them to rush into one 

 of the boxes blindly and without attempt at discrimination, 

 the narrowing of the space simply increased their efforts to 

 discriminate. The common mouse when subjected to simi- 

 lar experimental conditions is likely to be frightened by being 

 forced to approach the entrances to the boxes, and fails to 

 choose ; it rushes into one box directly, and in consequence 

 it is as often wrong as right. The dancer always chooses, 

 but its eagerness to choose is markedly increased by the 

 restriction of its movements to a narrow space in front of 

 a 



