LIGHT DISCRIMINATION IN THE ENGLISH SPARROW 103 



tion habit. The habit might appear at any time and the ob- 

 server always had to be alert lest the habit get firmly fixed. If 

 it did become fixed it was very difficult to break. It is evident 

 the sparrow forms the habit of choosing by position much more 

 easily than the habit of choosing by visual discrimination. The 

 form of position habit which appeared most frequently was that 

 of alternating from one side to the other without regard to the 

 illumination. But the observer found that the birds learned 

 also to go twice to one side, then twice to the other side, etc. 

 A few times when the order required three choices in succession 

 to one side, the birds would invariably want to go three times 

 to the other side. The experimenter planned to try more com- 

 plicated orders and see if the birds could be trained to learn the 

 habit. Lack of time prevented her carrying out this part of 

 the investigation. 



(d) Mental instability. The sparrows exhibited three quite 

 distinct types of mental instability; all of which were sources 

 of considerable trouble to the observer. At times the birds 

 would go to one side or the other apparently without trying to 

 discriminate. This is the first type. The second type of mental 

 instability was the persistence in going to one side. When they 

 would persist in this the experimenter found it quite impossible 

 to do anything with them. The third type might be termed 

 stubbornness or stupidity. When they would get stubborn or 

 stupid they would simply refuse to move. They would pay no 

 attention to an electric shock. The observer would force them 

 around through the apparatus though the results obtained on 

 such days were useless. 



The experimenter noticed that all the birds seemed to have 

 these periods of mental instability though they did not all have 

 them at the same time. One day a bird would record an almost 

 perfect series and the very next day a series of failures. It was 

 noticeable that such stupidity nearly always succeeded a period 

 of unusually good work on the part of the bird. The bird usually 

 recovered from this stupidity as quickly as it had come on. 

 Then the bird would continue the usual method of procedure as 

 though nothing unusual had happened. A few times they re- 

 covered during a day's series and the last few results would be 

 very satisfactory, while the first of the series were failures. 

 The question which came to the mind of the experimenter was 



