258 The Animal Mind 



and forms because they have been previously fed from them, 

 exhibit behavior which belongs to this class (130). The 

 method was used also by Yerkes in the experiments to test 

 brightness, color, and form discrimination in the dancing 

 mouse, described on pp. 145 and 197. Yerkes prefers to 

 establish discrimination by associating disagreeable rather 

 than agreeable experiences with one of the alternatives, 

 finding that the motive thus constituted works with greater 

 uniformity. Hence his mice were given slight electric shocks 

 when they made the "wrong" choice, instead of being fed 

 when they made the " right" one. He describes three dif- 

 ferent types of behavior on the part of the mice in making 

 the choices, which he calls choice by affirmation, choice by 

 negation, and choice by comparison. The first is illustrated 

 when the mouse enters the right compartment at once, the 

 second when it goes to the wrong compartment and turns 

 away from it, the third when it vacillates for some time be- 

 tween the two (469). 



90. Comparison of Methods 



The methods just described have something in common 

 with, and something different from, the puzzle-box method. 

 In both cases a particular object, offering certain peculiarities 

 to the senses, and distinguished from other objects, ultimately 

 comes to occupy the focus of consciousness ; but in this method 

 of choice, the other objects are themselves connected, either 

 by instinct or acquired impulses, with a particular reaction 

 which has to be checked. No definite tendency has to be in- 

 hibited in the puzzle-box method; it is only necessary for 

 random movements to be dropped off. On the other hand, 

 these experiments where inhibition becomes dependent on 

 the presentation of a particular stimulus, differ from tests 

 like those on the hermit crabs or the water scorpion, in that the 



