STIMULI DURING DELAYED REACTION IN DOGS 269 



that of the average of experiments of the Al type that the 

 indications of the use of olfactory cues were negative. The 

 question of rhythm could be applied here, but no special checks 

 were given. However, checks on the simpler type of ' Light 

 Out at Release" coming immediately after the close of these 

 series showed no evidence of rhythmic choice. There was no 

 reason to think that the dog adopted a rhythmic choice for 

 a five second delay, when he did not for a shorter delay period 

 that was being used in experiments carried on at the same time. 



Ten Seconds Delay. Al — On October 27th, 1913, the series 

 of trials with ten seconds delays under the type Al were begun 

 and extended to November 19th, 1913. The results of fifty 

 trials showed only twenty-five successful reactions. This was 

 evidently owing to the breaking down of the cues to the middle 

 compartment, and a return to a similar type of problem was 

 suggested. Accordingly the ; Two Light ' experiments were 

 employed again to determine what length of delay might be 

 obtained, with a view of applying the resulting training when 

 a return of the " Three Light " experiment should be made. 



A2 — On January 7th, 1914, the ten second delay was again 

 tried under the type A2, and the benefit of training on the "Two 

 Light" tests became apparent. The first fifteen trials showed 

 ten correct reactions, of which the first five were successful. 

 In the next series of ten trials on January 10th, 1914, all were 

 successful. The 80% average showed that the dog had attained 

 practical mastery of the problem. The likelihood of rhythmic 

 choice of compartments was prevented by choosing beforehand 

 a certain order and following it closely. No simple rhythm 

 could follow the picked succession, viz., 1, 2, 1, 3, 2, 2, 3, 1, 1, 

 3, 2, 3, 3, 2, 1. 



Longer Delays. — Scattered series of trials of fifteen seconds 

 delay, or longer, were made on days when the dogs' attention 

 was very keen. On November 15th, 1913, five trials, Condition 

 Al, with a fifteen second delay were all successful. On January 

 9th, 1914, ten trials with twenty seconds delay, Condition A2, 

 were all successful. As the interest of the experimenters was 

 along the line of further reducing the possible cues by which 

 the association might be made, no further trials were given 

 to demonstrate the mastery of longer periods of delay with 

 such complexity of cues as Condition Al and A2. However, 



