4 JOHN B. WATSON AND MARY I. WATSON 



(2), as will appear in Experiment II, the failure to get discrim- 

 ination at all between yellow and blue under similar circum- 

 stances. In other words if both colors used in Experiment I 

 had possessed stimulating value, no habit would have been 

 formed under the conditions there obtaining. 



Since at the completion of the above set of tests we had no 

 suspicion that the red was not stimulating the animals, we began 

 control experiments which were designed to show whether the 

 animals were responding to the difference in wave length or to 

 the difference in intensity. We had planned a' rather wide series 

 of tests. We had intended to leave the red at full intensity 

 and then gradually to lessen the intensity of the green with the 

 rotating sector, and then to repeat the procedure, allowing 

 green to remain at the standard intensity. It was hoped either 

 to establish the fact that the habit would maintain itself regard- 

 less of the intensity factor, or that at some point where the 

 intensities were equal for the animal, the habit would break 

 down. A few preliminary tests were taken with such astonish- 

 ing results that we had completely to re-envisage the problem. 

 We cite a few of the experiments: — 



1911. 



March jth. Red full intensity. Green cut to 11% of full 

 intensity. 15 trials. 93% correct. 



March Sth. Green full intensity. Red cut to 11% of full 

 intensity. 15 trials. 100% correct. 



March gth. Red full intensity. Green cut to 2.7% of full 

 intensity. 11 trials. 40% correct. Complete loss of discrim- 

 ination. Then immediately afterwards 9 trials were given with 

 both stimuli at full intensity. 100% of correct choices. 



March 10th. Conditions as beginning of test on previous day. 

 15 trials. 53% correct. Complete loss of discrimination. 5 

 trials were then given with both stimuli at full intensity. 100% 

 correct. 



March nth. Normal series. 15 trials. 100% correct. 



From March nth to May 16th certain experiments were 

 tried to determine the effect of external illumination upon the 

 discrimination. These experiments were so unsatisfactory that 

 mention of the results is omitted. By June 5th the animals 

 were again trained to discriminate perfectly between red and 



