STIMULI DURING DELAYED REACTION IN DOGS 265 



by the use of very attractive stimuli, such as (1), the smell of 

 meat, (2), waving a handkerchief, and (3), a whistle call, the 

 dogs gave very close attention and could bridge delay periods 

 of five seconds duration. 



The work of the writer falls into two main heads, (1), the 

 " Training Experiments," to establish the Light Association and 

 (2), the trials of " Delayed Reaction." 

 1. Training Experiments. 



These experiments were given to familiarize the dogs with 

 the electric light as a stimulus to reaction, in addition to the ones 

 they had already learned. This was done by combining the 

 light stimulus with a familiar one and gradually dropping out 

 the familiar one and leaving only the lights as a stimulus. When 

 the dogs came to react correctly to the stimulus when it re- 

 mained during the entire trial, the delay periods were introduced 

 in which the dog was forced to make the reaction when the 

 stimulus was absent. These trials were recorded separately 

 from the delay trials only in the "Three Light" experiments. 

 While some such trials were given during the ' Two ' and 

 " Four Light " experiments, they were too few to be discussed 

 under this separate head, but are mentioned at the beginning 

 of the corresponding " Delay Experiments." 



"A" Al — The series of trials of this type extended over the 

 period between October 4th, and November 19th, 1913. The 

 curve representing the learning period for the discrimination of 

 the three compartments was very short and steep. By October 

 25th, perfect mastery was gained. The results of the series 

 up to October 25th are as follows: 50%, 25%, 25%, 73%, 80%, 

 90%, 80%, 100%, 100%. Every succeeding series, totaling 

 eighty trials, gave 100% results. As stated before, the choice 

 of the order of the compartment to be used was determined 

 in advance of the series and care was taken to avoid any possible 

 simple rhythmic succession of choices. 



A2 — To avoid the possibility that the dog was gaining cues 

 to the proper reaction from the olfactory stimulus of the food 

 in the bowl, the problem was again taken up on January 12th, 

 1914, almost two months after the former experiments had been 

 stopped. In these trials, the food was not given until after 

 the reaction had correctly taken place. Four series (twenty 

 trials) from January 12th, to February 9th, 1914, were given 



