The Sense of Sight : Brightness Vision 131 



physiological conditions of the animal were during this pe- 

 riod of choosing, comparative psychology and physiology 

 would advance by a bound. 



If the conditions at the entrances of the two boxes were 

 discriminable, the mouse usually learned within one hundred 

 experiences to choose the right box without much hesitation. 

 Three distinct methods of choice were exhibited by different 

 individuals, and to a certain extent by the same individual 

 from time to time. These methods, which I have desig- 

 nated choice by affirmation, choice by negation, and choice by 

 comparison, are of peculiar interest to the psychologist and 

 logician. 



When an individual runs directly to the entrance of the 

 right box, and, after stopping for an instant to examine it, 

 enters, the choice may be described as recognition of the 

 right box. I call it choice by affirmation because the act of 

 the animal is equivalent to the judgment " this is it." If in- 

 stead it runs directly to the wrong box, and, after examining it, 

 turns to the other box and enters without pause for examina- 

 tion, its behavior may be described as recognition of the wrong 

 box. This I call choice by negation because the act seems 

 equivalent to the judgment "this is not it." Further, it 

 seems to imply the judgment " therefore the other is it." In 

 the light of this fact, this type of choice might appropriately 

 be called choice by exclusion. Finally, when the mouse runs 

 first to one box and then to the other, and repeats this any- 

 where from one to fifty times, the choice may be described as 

 comparison of the boxes; therefore, I call it choice by com- 

 parison. Certain individuals choose first by comparison, 

 and later almost uniformly by affirmation and negation. 

 Whenever the conditions are difficult to discriminate, choice 

 by comparison occurs most frequently and persistently. If, 

 however, the conditions happen to be absolutely indiscrim- 



