RATE OF LEARNING IN THE CHICK 121 



are designated by the letter s (sensitive) placed after their num- 

 bers in table III, the latter by the letter i (insensitive). Tests 

 were then begun with three sensitive chicks, Nos. 6i, 62, and 

 66, and with three insensitive ones, Nos. 63, 64, and 65, under 

 the medium condition of discrimination and with a weak stimulus. 

 Unfortunately, Nos. 63 and 64 died before the tests were com- 

 pleted. No. 65, however, required 150 trials for perfect dis- 

 crimination while each of the sensitive chicks required exactly 

 90 trials. The loss of the two insensitive chicks makes a definite 

 conclusion impossible, yet all our work with weak stimuli agrees 

 with the result of the records of these four chicks. It is prob- 

 able, therefore, that the chicks which were most sensitive to 

 the electric stimulus were the ones which learned most rapidly 

 under the influence of weak stimuli. 



Let us turn now to the results of strong stimulation. Should 

 the sensitive chicks be those which failed under the difficult 

 condition of discrimination and strong stimuli they should be 

 slowest to learn with the same stimuli and medium difference 

 of illumination of the two screens, since it was already proved 

 that a strong stimulus increased the learning rate under this 

 condition. Three sensitive chicks (Nos. 67, 68, and 69) and 

 three insensitive ones (Nos. 70, 71, and 72) were, therefore trained 

 under this condition. An examination of their records shows 

 that the sensitive chicks required an average of 40 trials for 

 learning to discriminate between the two screens, while the 

 insensitive ones required 53.33 trials. Evidently, therefore, 

 sensitiveness to the stimulus was not the condition which pre- 

 vented rapid learning under a strong stimulus. 



At the close of these experiments with sensitive and insen- 

 sitive chicks there seemed to be no explanation for the divergent 

 results under the third, or difficult condition of discrimination. 

 The behavior of the chicks indicated, however, that the pain 

 stimulus impressed the memory of those that failed so deeply 

 and permanently that, after a few experiences of it, they avoided 

 the electric wires completely and would no longer attempt to 

 escape from the experiment box. This observation, based on 

 the chicks' behavior, receives striking confirmation from the 

 records. The records of the successful chicks in the group 37-41, 

 inclusive, show that in their first fifty trials each chick received 

 an average of 20.4 pain stimuli, while chick 42, which failed, 



