20 



ROBERT M. YERKES 



Problem 3. Alternate left and right ends 



Settings 

 1. 

 2. 

 3. 

 4. 

 5. 

 6. 

 7. 

 8. 

 9. 

 10. 



Doors 



open 

 .5.6... 

 .5.6... 

 .4.5.6. 

 .4.5.6. 

 .1.2.3.4.5.. 

 .1.2.3.4.5.. 

 .2.3.4.5.6.7 

 .2.3.4.5.6.7 

 .3.4.5.6.7.8 

 .3.4.5.6.7.8 



8.9 

 8.9 



No. of 

 doors open 



9 



2 

 6 

 6 

 5 

 5 

 6 

 6 

 6 

 6 



No. of 

 right door 

 .5 

 .6 

 .4 

 .9 

 .1 

 .5 

 .2 

 .7 

 .3 



Problem 4. Middle 



Doors No. of No. of 



Settings open doors open right door 



1 4.5.6.7.8 5 6 



2 1.2.3 3 2 



3 1.2.3.4,5.6.7.8.9 9 5 



4 2.3.4.5.6 5 4 



5 6.7.8 3 7 



6 3.4.5.6.7.8.9 7 6 



7 7.8.9 3 8 



8 1.2.3.4.5.6.7 7 4 



9 2.3.4 3 3 



10 3.4.5.6.7 5 5 



It was my aim so far as possible to present to a given subject 

 each day the ten settings under a given problem in order, with- 

 out interruption. If for any reason the series of observations 

 had to be interrupted, it was resumed at the same point subse- 

 quently. Occasionally it was found desirable or necessary to 

 present only five of the series of ten settings in succession and 

 then to interrupt observations for an interval of a few minutes 

 or even several hours. But as a rule it was possible to present 

 the series of ten settings. All things being considered, it proved 

 more satisfactory to give only ten trials a day to each subject. 

 Frequently twenty and rarely thirty trials were given on the 

 same day. In such cases the series of settings was simply re- 

 peated. The only pause between trials was that necessary for 

 resetting the entrance doors and replenishing the food which 

 served as a reward for success. 



