LIGHT DISCRIMINATION IN THE ENGLISH SPARROW 107 



this caused a break in the order. It looked as though he had 

 forgotten which light he had chosen before. It would be inter- 

 esting to experiment further in detail upon this question. But 

 from the very limited material at hand, the observer is inclined 

 to think that the birds do not retain visual impressions very- 

 long at a time. 



IV. QUESTIONS SUGGESTED BY THIS INVESTIGATION. 



The question arose as to whether or not the birds would have 

 reached their threshold of discrimination in less time if the inter- 

 mediate steps were omitted. That is to say — train the bird to dis- 

 criminate the lights with wide differences in intensity. Then make 

 the difference very small and see if the bird could not learn to make 

 the discrimination in less time than was required to pass through 

 all the intermediate steps. The observer thinks that a great 

 number of the intermediate steps might be omitted in the earlier 

 part of the experiment when the differences in the intensities of 

 the lights were large. Female VI and Male V were trained to 

 choose the darker of the two lights. Female VI learned to 

 choose the darker of the two lights when they were 162 cm. 

 apart, which made the darker of the two lights very dim. Male 

 V learned to choose the darker of the two lights when they were 

 60 cm. apart and learned the problem in a shorter time than did 

 Female VI. It might have been better to have omitted all the 

 work with the wide difference in intensity for Female VI and 

 begun where Male V began. The results of Male V might have 

 been due to the fact that the darker of the two lights was not 

 so dark as it was for Female VI. It may have been easier for 

 the bird to learn to choose a light of medium intensity, than it 

 was for Female VI to learn to choose a light of extremely low 

 intensity. However, the small steps seemed to be essential as 

 the birds neared the threshold. In one case the observer de- 

 creased the difference in intensity too much by one step. The 

 bird seemed absolutely unable to make the discrimination after 

 it had been at the problem a long time. But when the lights 

 were shifted back to their former position and then the differ- 

 ence in intensity decreased step by step, the bird experienced 

 no difficulty in making even finer discriminations. So it seems 

 that the tests at intermediate intensities were essential and that 

 practice was an important factor in learning. 



