222 ROBERT. M. YERKES AND CHARLES A. COBURN 



After six hundred trials had been given to each individual 

 by use of the series of settings presented on page 192, under 

 problem 4, it was apparent that the animals could succeed 

 in solving the problem only by acquiring a definite habit for 

 each particular setting, and it was further evident that the 

 settings including seven and nine open doors were extremely 

 difficult for the animals. For these reasons it was decided to 

 present a modified series of settings in which the groups should 

 consist of either three or five open doors. Two hundred trials 

 were given with the new series of settings, and the settings 

 themselves, as well as the results obtained, appear at the bottom 

 of tables 9 and 10. 



Two important conclusions are justified by these results. 

 First, that the pigs, in so far as they had succeeded in responding 

 correctly to the middle door, had reacted to particular settings. 

 And second, that with sufficiently prolonged training they could 

 perfectly solve the problem of the middle member of a series, 

 if the total number in a group of open doors did not exceed five. 

 As a matter of fact, no series of ten correct choices was obtained 

 with either individual because of the surprisingly strong and 

 persistent influence of the original settings. 



Let us consider, for example, setting 3. This originally con- 

 sisted of the group 1.2.3.4.5.6.7, in which no. 4 was the box to be 

 entered. In the modified settings, this group was changed to 

 3.4.5.6.7, consequently, the box to be entered was 5 instead 

 of 4. Now, whereas in the case of setting 1 which remained 

 unchanged, the female made only one mistake in twenty-one 

 trials subsequent to the modification of the settings, in the 

 case of setting 3 she chose wrongly in all except three of the 

 twenty-one trials, and this in spite of the fact that in the case 

 of settings 2 and 5, both of which involved five open doors, she 

 chose correctly sixteen times out of twenty-one. Similarly in 

 the case of setting 6, in which originally all nine of the doors 

 were open, whereas in the modification only doors 1, 2, 3, 4 

 and 5 were used, both the female and the male chose correctly 

 only once in twenty-one trials. 



Although the above conclusions are of primary importance, 

 further examination of the data of tables 9 and 10 should throw 

 additional light on the reactive capacity of our subjects. 



We shall consider the materials according to the number of 



