STIMULI DURING DELAYED REACTION IN DOGS 267 



the two phases, Al and A2, depending on the manner of giving 

 the food, were recorded separately. 



Al — Ninety trials of this type, i. e. having the food placed 

 in the compartment before reaction, were given and seventy- 

 one were correct. These trials extended from October 18th, 

 1913 to November 19th, 1913, and show that practical mastery 

 had been gained. Perfect mastery could never be attained 

 because the factor of attention in the ■ dog was variable and, 

 hence, if he did not see the stimulus, at release, he was without 

 a cue and depended on chance. In the former tests, perfect 

 mastery was shown because the stimulus was always there and 

 could not be missed when leaving the release box. Several 

 series of five trials were all correct, but longer series showed 

 at best, only 80% of the reactions as correct. 



A2 — In order to test the memory of. the association formed, 

 and also to avoid the possibility of olfactory stimuli from 

 food in the compartments, trials in which the food was given 

 after correct reactions were taken up on February 9th, 1914, 

 and extended over to February 16th, 1914. A series of ten 

 trials gave 80% correct reactions and showed that the associ- 

 ation was not based on olfactory cues in any appreciable extent. 

 The question of rhythm kept coming up as a possibility, so 

 check trials were given on each of the three compartments to 

 see if this change of rhythm would cause a falling off of results, 

 and if such a falling off should come, to see if changing the 

 rhythm "was the cause. Forty tsials were given on No. 1 com- 

 partment with only 50% of correct results on February 12th, 

 1914. This falling off in results cannot, however, be laid to 

 the changing of the rhythm. Just previous to the trials, the 

 dog had run into No. 1 when the light was on and had touched 

 the hot electric bulb with his nose and received a slight burn. 

 As a result he avoided No. 1 constantly for the first ten trials, 

 and for five of the next ten. The last twenty trials showed 

 fifteen correct reactions of which the last five were successive. 

 The later mistakes were due rather to the habit of changing, 

 than to the following of any rhythm. A check of ten trials 

 on No. 3 compartment followed on February 14th, 1914 and 

 60% were successful, the last five being in succession. The 

 four mistakes did not follow any rhythm for the dog went to 

 No. 2 three times in succession and the fourth time to No. 1 . 



