STIMULI DURING DELAYED REACTION IN DOGS 287 



In condition "B, Three Lights," it is noticed that compart- 

 ments No. 2 and No. 3 are discriminated equally well and that 

 No. 1 is the one not so well discriminated. This failure on No. 1 

 was due to a long period of fear of the light there, as the dog 

 had burnt his nose on it at the beginning of the "B" trials. The 

 equal discrimination of No. 2 and No. 3 shows that the training 

 on No. 2 received in condition "A" had borne fruit. In condi- 

 tion "C — Three Lights," compartment No. 2 was discriminated 

 25% better than either No. 3 or No. 1 .In both compartments, 

 the dog had lost the cues to their discrimination several times 

 and had been given special training on them. The previous 

 training on No. 2 was shown in the results of the trials. This 

 trial in the power of discriminating No. 2 from the others is a 

 proof of the benefit of special training in habit formation, for 

 the habit of going there on stimulus, had become so firmly 

 fixed that errors became steadily less, and passed in strength, 

 the habits that caused him to go to the others on stimulus. 



In the "Two Light" experiments, condition "A," "B" and 

 "C" show better discrimination of No. 1 than of No. 3 by about 

 18%. This favoritism was due to the fact that the light in 

 No. 3 was too bright, and after changing to a dimmer one, it 

 took over a week before the fear of No. 3 was sufficiently over- 

 come to allow the dog to enter freely whenever the stimulus 

 was given there. As the "Two Light" trials took place in a 

 period of only two or three weeks, this trouble with No. 3 

 materially affected the general results of a large number of trials. 



In the trials of condition "AD" and "CD" that took place in the 

 period between December 12th and 15th, 1913, the results were 

 reversed and No. 1 was the one that was not so well discrimi- 

 nated. In condition "AD" the difference was too small to be 

 noticed but in condition "CD" a difference of 11% was found. 

 This difference was due to the fact mentioned in the "Three 

 Light" types, i. e. that the dog had burned his nose on December 

 15th, and hesitated to go to No. 1 after that. This set of ex- 

 periments was concluded on this day and the "Three Light" 

 type resumed, but the fear of No. 1, however, was carried over 

 and effected the records there. In all these trials, care was 

 taken that, while rhythmic successions of choices of compart: 

 ments was avoided as much as possible, the number of chances 

 was approximately the same for each compartment. The 



