30 ROBERT M. YERKES 



the electric shock was introduced as a means of compelling 

 attention to the visual stimuli and of encouraging careful com- 

 parison and appropriate reaction. Even from the start, the 

 electric stimulus served this purpose admirably. It at once 

 rendered the birds more alert, careful, attentive, and active. 

 The writer's notes record, " In two weeks the doves apparently 

 have learned nothing, but to-day as the result of four trials 

 with electrical stimulation, each seemed to attempt to discrim- 

 inate between the light and the dark chambers. 



It was decided, on the basis of the preliminary observations, 

 that the doves should be required to choose the lighter rather 

 than the darker of the two compartments. 



Number 3, the female, was at the outset much less wild and 

 more timid than number 4, the male. It was much easier for 

 the experimenter to catch her in the living-cage than to catch 

 him, but when in the experiment-box, she was very much more 

 disturbed, excitable, and liable to discouragement than he. By 

 contrast, then, the' female may be described as tame and timid, 

 the male as wild and bold. But it should be added that neither 

 bird was sufficiently wild to be difficult to handle. 



On February 28th, 1914, systematic, regular experiments were 

 begun, with the use of both food and the electric shock. Both 

 birds worked well in the six trials which were given. Only one 

 bird was used at a time, and it was given its trials in succession, 

 with from one-half to one minute interval for feeding between 

 choices. In comment on this day's reactions, the writer's notes 

 state that " The use of the electric shock discreetly and infre- 

 quently has transformed the birds from time-wasting and care- 

 less subjects to active, alert, constantly moving reactors. This 

 modification of method evidently means a saving of an immense 

 amount of time to the experimenter. It enables him to command 

 the attention of his subject instead of having to beg for it by 

 the offering of food. Food, however, is serving an excellent 

 purpose in the work, for each bird comes to its task hungry 

 and usually feeds between trials." 



On March the 2nd, the number of trials for each bird was 

 increased to ten, and it was subsequently found that as many 

 as fifteen or even twenty trials could be given in succession 

 without overfatiguing the subjects and with excellent results. 



Table 1 presents two sample detailed records of the daily 



