Modification by Experience 301 



in space, but is always the furthest to the right or left of 

 all the compartments used in the experiment, the learning 

 is still easy. The animal has only to combine the habit of 

 turning to the right or left with the observation as to what 

 compartments have their entrance doors raised : a compart- 

 ment with closed doors offers no stimulus. Thirdly, even 

 the problem " second from the left," or right, might, it 

 would appear, be solved without the use of a memory idea. 

 The learning need involve only (a) the habit of turning to 

 the left or right, and (b) the habit of reacting negatively to 

 the open door furthest in this direction. The natural re- 

 sult of such a combined habit would be entering the door 

 next to the end door. The problem of entering always 

 the middle door of those open brings us closer to the use 

 of memory ideas. An animal that had solved this problem 

 would, on being confronted with the series of doors, find 

 itself in an attitude representing a balance between the 

 impulse of turning to the right and that of turning to the 

 left. "Middleness" means a slight impulse to turn in 

 one direction, offset by an equal impulse to turn in the 

 other direction. Now the characteristic by which this 

 situation differs from the other situations, involved in the 

 simpler problems, is that the animal must not move at once, 

 but must wait and assume the balanced attitude before 

 moving. In the case of the other problems, he can start 

 off immediately. Here an attitude must be revived before 

 there is any actual movement. Just as in the Delayed 

 Reaction Method success means, if the animal moves 

 during the interval of delay, that it is able to revive an inner 

 attitude which means motion towards the light, so here 

 success means ability to revive an inner attitude which 

 means movement towards the middle, a balance beween 

 right and left movements. 



